WO1999051995A9

WO1999051995A9 - Imaging system for detecting underground and underwater objects and associated method

Info

Publication number: WO1999051995A9
Application number: PCT/US1999/005725
Authority: WO
Inventors: Peter J Wilk
Original assignee: Wilk Patent Dev Corp
Priority date: 1998-03-17
Filing date: 1999-03-12
Publication date: 2000-01-13
Also published as: WO1999051995A3; AU5078799A; CA2324084A1; BR9908879A; WO1999051995A2

Abstract

A method for detecting hidden objects utilizes a plurality of electromechanical transducers including at least one electroacoustic pressure wave generator (88) and at least one acoustoelectric sensor (92) above a selected ground or water surface or a surface of an object located underground or underwater. Accordingly, the method is useful for detecting underground or underwater objects. Pursuant to the method, locations of the transducers relative to one another are determined, the pressure wave generator is energized to produce an outgoing pressure wave, and the outgoing pressure wave is transmitted through the selected surface. Incoming pressure waves are detecting which are reflected by hidden surfaces generally below the selected surface in response to the outgoing pressure wave. The incoming pressure waves are analyzed (38) to determine three-dimensional shapes of hidden objects disposed below the selected surface, whether underground or underwater. Various views of the hidden objects are displayable on a video monitor (58).

Description

IMAGING SYSTEM FOR DETECTING UNDERGROUND

AND UNDERWATER OBJECTS

AND ASSOCIATED METHOD

BACKGROUND OF THE INVENTION

This invention relates to an imaging system utilizing sonic or ultrasonic pressure

waves for sensing purposes. More particularly, this invention relates to such a system for use

in detecting and surveying generally invisible surfaces, whether those surfaces are

underground or underwater. This invention also relates to an associated method.

There are many situations where objects are visually inaccessible. Such objects may

be buried underground or sunken underwater. It is frequently of great importance to various

interested people to determine the exact location of such buried or sunken objects but also to

be able to obtain a view of such objects from a location on the surface of the earth.

One of the great problems in the world today is the presence of substantial numbers of

land mines in various regions of the world. These mines were placed during armed conflicts,

guerilla and civil wars and although those conflicts have been terminated in many cases, the

land mines remain. The land mines are particularly dangerous for children.

Treasure hunters' first and sometimes primary chore is determining the locations of

valuable artifacts. A considerable number of artifacts of interest to archeologists and/or

paleontologists remain underground or underwater. These artifacts are detected only with

considered trial and error, if not happenstance. With respect to underwater treasure hunting,

this state of affairs has not changed even with the recent introduction of submersibles and

robotic cameras to scout for sunken ships.

Despite these modern solutions, the hunt for underwater artifacts remains impeded by

the difficulty of detecting objects underwater when available light levels are low. Such low light levels exist at great depths and in shallower waters where silt and other waterborne

particles scatter light. Of course, visual detection is completely impeded where artifacts have

been covered by sand or silt. Although ferrous artifacts can be located in such conditions with

the aid of magnetic detectors, non-ferrous artifacts such as bronzes, pottery, gold and silver

remain undetectable.

OBJECTS OF THE INVENTION

An object of the present invention is to provide an automated sensing system which

facilitates detection of objects underground and/or underwater.

An associated object of the present invention is to provide such imaging system which

facilitates identification of obj ects which are located underground and/or underwater.

It is a more specific object of the present invention to provide such an imaging system

capable of detecting objects inside other objects which are underground and/or underwater.

A further object of the present invention is to provide an associated imaging method

enabling the visual inspection of underground and/or underwater objects.

Another object of the present invention is to provide such an imaging system and/or

method which is unaffected by existing light levels.

A more particular object of the present invention is to provide such a sensing system

which facilitates the detection of land mines. Such imaging system preferably facilitates

identification of underground objects and may be capable of determining the type of land

mine. This information is useful in selecting a method of destroying detected land mines.

enabling the visual inspection of underground objects.

These and other objects of the present invention will be apparent from the drawings and descriptions herein.

SUMMARY OF THE INVENTION

These objects are attained in a method for detecting hidden objects which utilizes a

plurality of electromechanical transducers including at least one electroacoustic pressure wave

generator and at least one acoustoelectric sensor above a selected surface. The selected

surface may be a land or ground surface or a water surface or, alternatively, the selected

surface may be an outer or upper surface of an object which is located underground or

underwater. Pursuant to the method, locations of the transducers relative to one another are

determined, the pressure wave generator is energized to produce an outgoing pressure wave,

and the outgoing pressure wave are transmitted through the selected surface. Incoming

pressure waves are detecting which are reflected by hidden surfaces generally below the

selected surface in response to the outgoing pressure wave. The incoming pressure waves are

analyzed to determine three-dimensional shapes of hidden objects disposed below the selected

surface, whether underground or underwater. Various views of the hidden objects are

displayable on a video monitor.

Generally, the three-dimensional shapes as calculated during the analysis of the

incoming reflected pressure waves are stored in a memory, which permits selection of

different views of the objects, from different angles and at different magnifications. In

addition, a selection function may be employed to view internal surfaces of detected objects,

i.e., to remove or filter out overlying surfaces. The stored three-dimensional shapes may be

compared automatically to previously stored three dimensional shapes of known classes of

objects, thereby enabling the automatic recognition and identification of hidden objects which

are buried in a land mass or located underwater. For example, land mines may be detected and identified, thereby facilitating selection of appropriate deactivation procedures. Where

the hidden objects are buried or sunken artifacts, the insides of the objects may be examined

by the automatic pattern recognition function, thereby determining whether valuable objects

are hidden behind the overlying surfaces.

In many applications of the present invention, it is advantageous to have the

electromechanical transducers all attached to a common carrier. In that case, the disposing of

the electromechanical transducers above the selected surface includes moving the carrier into

position above the selected surface. The carrier may be spaced from the selected surface, for

example, where the selected surface is a surface of an underwater object or where the carrier is

located above a land surface. Alternatively, the carrier may be placed in contact with the

selected surface, for example, where the selected surface is a land surface of a certain variety.

The locations of the transducers are determined, in many application of the method, after the

placing of the carrier in contact with the selected surface. In that event, determining the

locations of the transducers relative to one another includes analyzing pressure waves

transmitted directly from the pressure wave generator to the sensor.

Where the carrier is substantially rigid, the disposing of the electromechanical

transducers above the selected surface includes holding the carrier above and spaced from the

selected surface. This scenario is applicable where the selected surface belongs to an

underwater object or when the selected surface is a ground surface below which suspected

land mines are located. In the latter case, the carrier may be a frame or truss work extending

outwardly from the front, rear or side of a land vehicle such as a tank or other all-terrain

vehicle. The carrier or frame may be movably mounted to the land vehicle for varying the

vertical distance between the transducers and an underlying ground surface. This may be necessary where the terrain is uneven. Also, the detection of underground objects such as

land mines may be facilitated by varying the spacing between the carrier and the ground

surface.

Where the carrier is mounted to an air-borne vehicle, the disposing of the

electromechanical transducers above the selected surface includes moving the air-borne

vehicle over a ground surface. Where the carrier and the electromechanical transducers are

air-borne, the disposing of the electromechanical transducers above the selected surface

includes suspending the carrier and the electromechanical transducers over the selected

surface.

Generally, it is contemplated that the outgoing pressure wave has a plurality of

different frequencies. The different frequencies may be produced and emitted at different

times. Alternatively, the different frequencies may be emitted simultaneously. Pursuant to

this alternative, selective detectors exemplarily including filters are used to separate incoming

pressure waves of different frequencies generated at reflective surfaces in response to

outgoing pressure waves of the respective frequencies. Where there are multiple

electromechanical transducers for generating pressure waves, these transducers may be

designed for producing pressure waves within respective ranges. Alternatively, each such

transducer may be capable of producing pressure wave of different frequencies in a

predetermined sequence or simultaneously.

Different kinds of information are obtainable by pressure waves of different

frequencies. For example, data pertaining to surface details are more readily obtainable by

higher frequency pressure waves inasmuch as pressure waves of higher frequencies yield an

enhanced resolution relative to pressure waves of lower frequencies. Pressure waves of lower frequencies may be relied on in an initial scanning step to determine whether there are any

objects in a predetermined size range beneath a ground surface. Subsequent scans at higher

frequencies are used to determine details of possible objects of interest.

In accordance with another feature of the present invention, the disposing of the

electromechanical transducers above the selected surface includes operating a remote control

robot to shift the transducers into a predetermined position above the selected surface. This

feature of the invention is useful where the transducer carrier moves along a path underwater

or over an area suspected of containing land mines.

Where the selected surface is a ground surface of a ground structure and the outgoing

pressure wave and the incoming pressure waves are ultrasonic, the method may further

comprise wetting a ground structure contiguous with the selected surface to facilitate

transmission of the outgoing pressure wave and the incoming pressure waves through the

ground structure.

In the detection of land mines, the transducer carrier may mounted to an air-borne

vehicle such as a helicopter or a balloon. In that case, the disposing of the electromechanical

transducers above the ground structure includes moving the air-borne vehicle over a ground

surface and suspending the carrier and the electromechanical transducers from the air-bome

vehicle. A human operator and a video monitor may be located in the air-borne vehicle.

Alternatively, the operator and the monitor may be remotely located. In the latter case, the

movement of the vehicle and the carrier over the land surface is effectuated by a remotely

controlled robot mechanism.

Where the outgoing pressure wave and the incoming pressure waves are ultrasonic, the

implementation of the invention is enhanced in many cases by wetting the ground to facilitate transmission of the outgoing pressure wave and the incoming pressure waves through the

ground.

Where the underground objects include land mines, the method may further comprise

detonating the land mines after identification of the underground objects as land mines. The

land mines may be marked and subsequently detonated. Alternatively, the carrier vehicle may

be equipped with small explosive charges which are deposited in an area about a detected land

mine and subsequently detonated under remote control when the area is clear of people.

A system for detecting objects such as land mines hidden underground comprises, in

accordance with the present invention, a carrier movable over a land surface and a plurality of

electromechanical transducers mounted to the carrier, the electromechanical transducers

including at least one electroacoustic pressure wave generator and at least one acoustoelectric

sensor. A source of alternating electrical current is operatively connected to the pressure

wave generator for energizing the generator to produce an outgoing pressure wave

transmittable to an effective extent through upper layers of a ground formation. Components

are operatively connected to the electromechanical transducers for determining locations of

the transducers relative to one another. These components may be the carrier itself, in the

case of a rigid carrier, or circuitry such as software-modified generic computer circuits for

computing the relative locations of the transducers from the transmission times and/or signal

strengths of pressure waves transmitted from the pressure wave generators) to the sensor(s).

A wave analyzer is operatively connected to the sensor(s) for analyzing incoming pressure

waves reflected by an underground surfaces in response to the outgoing pressure wave, to

determine three-dimensional shapes of underground objects. Also, a propulsion mechanism

is operatively connected to the carrier for moving the carrier over the land surface. The carrier for detecting land mines may take the form of a flexible web. For instance,

the web may be a rubber blanket which is rolled out over or dragged along a ground surface to

lie on a selected section of ground. Alternatively, the web may be the lower panel of a

container holding a fluid medium. The container may includes a substantially rigid upper

panel and flexible panels connected to the rigid panel. The fluid acts to press the lower panel

of the container into substantial conforming contact with an underlying ground surface.

Another system for underground surveying comprises, in accordance with the present

invention, a plurality of substantially rigid frames and a plurality of acoustoelectric sensors for

generating electrical signals encoding echo responses of underground surfaces. Each of the

frames carries at least one of the sensors, the sensors being disposable in effective physical

contact with underground structures upon an insertion of the frames through a ground surface.

An acoustic energy generator is disposable in effective physical contact (pressure-wave-

transmitting contact) with the underground structures, while position determination

componentry is operatively connected to the sensors for determining locations of the sensors

relative to one another. An electronic signal processor is operatively connected to the sensors

for analyzing the electrical signals in accordance with the determined locations of the sensors

to determine surfaces of an object hidden underground and for generating a video signal

encoding an image of the object. A video monitor is operatively connected to the processor

for displaying the image of the object.

The acoustic energy or pressure wave generator in this system for underground

surveying may be an electroacoustic transducer. In that case, the system further comprises an

a-c current generator operatively connected to the electroacoustic transducer for energizing the

electroacoustic transducer with an electrical signal of a pre-established frequency, preferably an ultrasonic frequency. This embodiment of the invention is particularly useful where the

ground formation or underground structures are wet. Wet ground formations naturally occur

in marshlands, clay deposits and below the water table and may be induced by injecting water

into a dry ground structure. Alternatively, the acoustic energy or pressure waves transmitted

through the underground structures may be generated by an explosive device.

A method for underground surveying comprises, in accordance with the present

invention, disposing an array of acoustoelectric sensors in operative contact with a ground

formation capable of transmitting pressure waves, thereafter determining physical locations of

the acoustoelectric sensors relative to each other and generating a pressure wave in the ground

formation, subsequently energizing the acoustoelectric sensors to generate a series of

electrical signals encoding echo responses of underground surfaces to the pressure wave,

automatically analyzing the electrical signals to generate a video signal encoding an image of

the surfaces, and feeding the video signal to a video monitor to thereby display the surfaces on

the monitor.

Where the sensors in this method are mounted to a plurality of substantially rigid

frame members, the disposing of the sensor array includes inserting the frames through a

ground surface and into the ground formation. Where the frame members each have an

elongate dimension, the disposing of the sensor array includes disposing the frame members

so that the respective elongate dimensions extend approximately parallel to a gravity vector or

at an acute angle with respect to the gravity vector.

Where the sensors are mounted to a carrier such as a fluid filled container, the

disposing of the sensor array includes disposing the container on the ground formation. The

container may have a wedge shape with a first wall and a second wall disposed at an angle relative to one another. The sensors are fixed to the second wall. In that case, the disposing

of the sensor array includes disposing the first wall in contact with the formation and the

second wall at the angle with respect to the first wall. The container may be disposed in an

arcuate configuration, e.g., a circle or a regular polygon, on the formation.

In order to facilitate the conduction of ultrasonic pressure waves through the ground

formation, a liquid such as water may be introduced into the formation. This step is generally

of special advantage where the ground formation is made of a dry material. In some cases, for

example, in marshlands, bogs, swamps, and clay deposits, the introduction into the ground

formation of a liquid such as water may be superfluous.

A system for surveying an underwater topography comprises, in accordance with the

present invention, an ultrasonic sensor array disposable in physical contact with a body of

water for generating electrical signals encoding ultrasonic echo responses of underwater

objects in the body of water. The sensor array includes a plurality of electromechanical

transducers in turn including at least one electroacoustic transducer and one acoustoelectric

transducer. The transducers are disposed in a configuration extending in at least two

dimensions. An a-c current generator is operatively connected to the electroacoustic

transducer for energizing the electroacoustic transducer with an electrical signal of a

pre-established ultrasonic frequency. Means are provided which operatively connected to the

sensor array for determining locations of the electromechanical transducers relative to one

another. A processor or computer is operatively connected to the sensor array for analyzing

the electrical signals in accordance with the determined locations of the electromechanical

transducers to determine surfaces of objects disposed at least partially in the body of water

and for generating a video signal encoding an image of the objects. A video monitor is operatively connected to the processing means for displaying the image of the objects.

It is generally contemplated that the sensor array of the system for surveying an

underwater topography includes a carrier such as a net or a rigid frame structure, the

transducers being mounted to the carrier. In either case, motive or propeller elements may be

attached to the carrier for applying a force to the carrier relative to the body of water. The

motive or propeller elements may be activated to move the carrier and the entrained sensor

array through the body of water, for example, below the surface. The motive or propeller

elements are optionally motor modules with wireless signal receivers for receiving

instructions from a surface or underwater vessel. Alternatively, in a simpler embodiment of

the invention, a ship or other vessel drags the carrier through the body of water, either along

the surface or below the surface, where wave action is reduced if not eliminated.

Where the electromechanical transducers include a plurality of electroacoustic

transducers disposed in a predetermined array, circuitry is provided for energizing the

electroacoustic transducers in a predetermined sequence. Thus, the processor is able to

associate any set of incoming reflected pressure waves with the particular transducer which

generated the pressure waves. The different transducer locations as well as multiple scanning

operations provide enhanced information for data processing purposes. This enables not only

the refinement of the image (increased resolution) but also enables the selection (by the

operator, usually) of different view angles.

Where the electromechanical transducers include a plurality of acoustoelectric

transducers or sensors disposed in a predetermined array, circuitry is provided for receiving

signals from the acoustoelectric transducers in a predetermined sequence. Because of this

structure, the processor processes multiple sets of incoming reflected pressure waves each associated with the particular sensor which detects the pressure waves. Again, the different

sensor locations as well as multiple scanning operations provide enhanced information which

enables image refinement and the selection of different view angles. Of course, information

utilized in image processing is maximized where the sensor array includes multiple distributed

pressure wave generators and multiple distributed pressure wave receivers.

The determination of transducer position may be implemented simply in the case of a

substantially rigid carrier. The electromechanical transducers are mounted to the carrier so

that the locations of the electromechanical transducers relative to one another are fixed by the

carrier. However, it is alternatively possible for the transducers to be disposed at variable

locations relative to one another. In that case, the instantaneous positions of the pressure

wave generators and the pressure wave receivers relative to each other are determined by

processing or analyzing additional electrical signals generated by the sensors or receivers in

response to pressure waves transmitted through the body of water directly from the

electroacoustic transducers or generators to the acoustoelectric sensors or receivers.

Where the electromechanical transducers include a single electroacoustic transducer

and a plurality of acoustoelectric transducers, the sensor array includes means for sampling

output signals of the acoustoelectric transducers in a predetermined sequence. Where the

electromechanical transducers include a plurality of electroacoustic transducers and a single

acoustoelectric transducer, the sensor array includes means for activating the electroacoustic

transducers in a predetermined sequence.

A method for surveying an underwater topography comprises, in accordance with the

present invention, disposing an array of electroacoustic transducers in operative contact with a

body of water, determining physical locations of the transducers relative to each other, and energizing the transducers to generate a series of electrical signals encoding echo responses of

underwater objects in the body of water, the echo responses corresponding to a multiplicity of

pressure wave paths from the transducers to each of the objects and back to the transducers.

The electrical signals are automatically analyzed to generate a video signal encoding an image

of the objects, the video signal being fed to a video monitor to thereby display the objects on

the monitor.

It is contemplated that the disposing of the transducers in operative contact with the

body of water includes deploying a carrier in the body of water, the transducers all being

attached to the carrier. The method may further comprise operating motive or propulsion

devices attached to the carrier, thereby moving the carrier relative to the body of water. The

motion may be translation parallel to an underwater surface or rotation to facilitate the

collection of ultrasonic data pertaining to a non-horizontal surface. In the latter case, the

operating of the propulsion devices includes differentially operating the propulsion devices to

change an orientation of the carrier relative to the body of water and relative to the objects.

Where the carrier is a net, the method further comprises operating the propulsion

devices to pull in opposing directions on the net to maintain the net in an extended

configuration.

Where the electromechanical transducers include a plurality of acoustoelectric sensors,

the energizing of the transducers includes receiving signals from the sensors in a

predetermined sequence.

Pursuant to another feature of the invention, determining the physical locations of the

transducers includes analyzing additional electrical signals generated by the sensors in

response to pressure waves transmitted through the body of water directly from selected transducers to the sensors. Preferably, the analyzing of the electrical signals includes

analyzing the electrical signals to determine three-dimensional shapes of the objects.

An ultrasonic imaging system for underwater surveying in accordance with the present

invention facilitates detection of underwater objects, even when the ambient light levels are

insufficient to allow visual inspection.

present invention, an ultrasonic sensor network disposable in physical contact with a body of

objects in the body of water. The sensor network includes a plurality of electromechanical

transducer. The elecfromechanical fransducers are disposed in an array which has at least two

transducer for energizing the elecfroacoustic transducer with an electrical signal of a

pre-established ultrasonic frequency. A position determination element is operatively

connected to the sensor network for determining locations of the elecfromechanical

transducers relative to one another. A processor is operatively connected to the sensor

network for analyzing the electrical signals in accordance with the determined locations of the

electromechanical fransducers to determine surfaces of objects disposed at least partially in

the body of water. The processor includes pattern recognition circuitry for comparing the

determined object surfaces with a stored electronic library of stored surface data to identify

the determined object surfaces as being consistent with a predetermined class of objects.

The system further comprises, in accordance with another aspect of the present

invention, a position determination circuit operatively connected to the processor for determining locations of the determined object surfaces relative to a global frame of reference.

A recording component is operatively connected to the processor and the position

determination circuit for recording locations of the determined object surfaces relative to the

global frame of reference. Thus, the latitude and longitude, as well as the depth, of a detected

object of interest may be recorded for future reference. The recording component may include

an electronic data store or, alternatively, a printer.

Where the underwater sensor network includes a carrier, with the transducers being

mounted to the carrier, the detection system further comprises one or more motors operatively

connected to the carrier for moving the carrier through the body of water. The motors may be

mounted directly to the carrier, in a self-propelled implementation, or to motor modules, or to

a surface or submarine vessel which then drags the sensor network carrier through the body of

water. The motor modules are provided with wireless signal receivers for receiving

instructions from a surface or underwater vessel.

The pattern recognition circuitry is operatively connected to the motor or motors for

arresting the motors upon detecting that one of the determined object surfaces falls into a

predetermined class of objects of interest. Thus, if something of particular interest is detected,

other investigations may be undertaken immediately to confirm the identity and the

importance of the find.

The processor may be located on the carrier itself or on a vessel which is pulling the

carrier through the body of water. Alternatively, the processor may be disposed at a more

remote location, on land, at sea or in the air. In that case, the sensor network may be linked to

the processor (and the processor to the motors) via a wireless communications link.

The various components of the processor, including the analyzer, are realized in a general purpose computer by generic processing circuits configured by programmed

instructions.

Where the elecfromechanical transducers include a plurality of acoustoelectric

transducers disposed in a predetermined array, the underwater detection system further

comprises means for receiving signals from the acoustoelectric transducers in a predetermined

sequence. Because of this structure, the processor processes multiple sets of incoming

reflected pressure waves each associated with the particular sensor which detects the pressure

waves. Again, the different sensor locations as well as multiple scanning operations provide

enhanced information which enables image refinement and the selection of different view

angles. Of course, information utilized in image processing is maximized where the sensor

array includes multiple distributed pressure wave generators and multiple distributed pressure

wave receivers.

present invention, steps of disposing an array of electroacoustic fransducers in operative

contact with a body of water, determining physical locations of the transducers relative to

each other, and energizing the transducers to generate a series of electrical signals encoding

echo responses of underwater objects in the body of water, the echo responses corresponding

to a multiplicity of pressure wave paths from the fransducers to each of the objects and back to

the fransducers. The method further comprises a step of automatically analyzing the electrical

signals to determine surfaces of objects disposed at least partially in the body of water. This

analyzing includes the step of comparing the determined object surfaces with a stored

electronic library of stored surface data to identify the determined object surfaces as being

consistent with a predetermined class of objects. In accordance with another feature of the present invention, further comprises the steps

of determining locations of the determined object surfaces relative to a global frame of

reference, and automatically recording locations of the determined object surfaces relative to

the global frame of reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is partially a schematic perspective view, partly broken away, and partially a

block diagram of an ultrasonic system for underground surveying, showing a plurality of

fransducer carriers or frames.

Fig. 2 is a schematic side elevational view of the system of Fig. 1, showing a

modification in use of the system.

Fig. 3 is a block diagram showing selected components of a wave analyzer and a

surface detector module shown in Fig. 1.

Fig. 4 is a schematic perspective view of a modified transducer carrier or frame.

Fig. 5 is a schematic perspective view of another modified fransducer carrier or frame.

Fig. 6 is a block diagram showing a specific variant of the system of Fig. 1.

Fig. 7 is a block diagram showing another variant of the system of Fig. 1.

Fig. 8 is a schematic perspective view of a system for underground surveying, in

accordance with the present invention.

Fig. 9 is a schematic perspective view of another system for underground surveying, in

accordance with the present invention.

Fig. 10 is a schematic perspective view of a transducer pad utilizable in an

underground surveying system in accordance with the present invention.

Fig. 11 is a schematic perspective view of an alternatively inflatable and collapsible frame member utilizable in an underground surveying system.

Fig. 12 is a schematic perspective view of an underground surveying system utilizing

the elements of Figs. 10 and 11.

Fig. 13 is a schematic perspective view of another alternatively inflatable and

collapsible frame member utilizable in an underground surveying system, showing the frame

member in a collapsed configuration.

Fig. 14 is a view similar to Fig. 13, showing the frame member of in an expanded

configuration.

Fig. 15 is a schematic perspective view of an underground surveying system utilizing

the elements of Figs. 13 and 14.

Fig. 16 is a schematic perspective view of a hand-held or hand-manipulable

underground surveying device.

Fig. 17 is a schematic perspective bottom view of a transducer carrier component

shown in Fig. 16.

Fig. 18 is a schematic perspective bottom view showing a modification of the

transducer carrier component of Figs. 16 and 17.

Fig. 19 is a partial elevational view of another modification of the transducer carrier

component of Figs. 16 and 17.

Fig. 20 is a partial elevational view of yet another modification of the transducer

carrier component of Figs. 16 and 17.

Fig. 21 is a schematic perspective view of transducer-carrying elements of a sonic

and/or ultrasonic object detection system in accordance with the present invention.

Fig. 22 is a schematic perspective view of transducer-carrying elements of another sonic and/or ulfrasonic object detection system in accordance with the present invention.

Fig. 23 is a schematic perspective view of transducer-carrying elements of a further

sonic and/or ulfrasonic object detection system in accordance with the present invention.

Fig. 24 is a schematic perspective view of transducer-carrying elements of a modified

Fig. 25 is a schematic perspective view of transducer-carrying elements of yet another

sonic and/or ultrasonic object detection system in accordance with the present invention.

Fig. 26 is a transducer-carrying pad and storage container of another sonic and/or

ultrasonic object detection system in accordance with the present invention.

Fig. 27 is a schematic perspective view of transducer-carrying elements of yet another

Fig. 28 is a partially a schematic perspective view and partially a block diagram of a

nautical ultrasonic imaging system in accordance with the present invention.

Fig. 29 is a block diagram showing components of a processing system depicted in

Fig. 28.

Fig. 30 is a block diagram of a preliminary signal processing circuit illustrated in Fig.

29.

Fig. 31 is a block diagram of an ultrasonic waveform generator shown in Fig. 29.

Fig. 32 is a block diagram of a digital-to-analog converter shown in Fig. 29.

Fig. 33 is a block diagram showing a specific variant of the system of Figs. 28 and 29.

Fig. 34 is a block diagram showing another variant of the system of Figs. 28 and 29.

Fig. 35 is a schematic perspective view of an ultrasonic pressure wave generating

and/or sensing unit utilizable in an ulfrasonic imaging system in accordance with the present invention.

Fig. 36 is a schematic perspective view of a carrier net and dedicated propeller units of

a modified ultrasonic imaging system in accordance with the present invention.

Fig. 37 is a schematic perspective view of a rigid carrier and dedicated propeller units

of another modified ultrasonic imaging system in accordance with the present invention.

Fig. 38 is a schematic perspective view of another rigid carrier of transducers of an

ulfrasonic imaging system in accordance with the present invention.

Fig. 39 is a block diagram similar to Fig. 29 and containing additional elements of a

processor and of an ulfrasonic imaging system in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in Fig. 1, a system for underground surveying comprises a plurality of

substantially rigid frames 12 each carrying a plurality of elecfromechanical transducers 14 for

generating electrical signals encoding ultrasonic echo responses of underground surfaces, for

example, a lid surface 16 (see Fig. 2) and a body surface 18 of an object UO buried

underground. Object UO might, for example, be a chest or an urn containing valuable

archeological objects.

Each frame 12 carries at least one ultrasonic transducer 14. Upon an insertion of the

frames through a ground surface 24, transducers 14 are disposed in physical contact with

underground structures 22 capable of transmitting ultrasonic pressure waves. As illustrated in

Fig. 2, the underground structures 22 may include a plurality of geologic layers 22a, 22b and

22c each capable of fransmitting ultrasonic pressure waves. In most cases, the material of the

underground structures incorporates significant quantities of water. Thus, the underground

mass may be a clay deposit, a marsh or a water-filled porous land mass. The water may be present naturally or supplied to the land mass in order to carry out the ulfrasonic sensing

techniques described herein.

Transducers 14 include one or more electroacoustic fransducers 26 and one or more

acoustoelectric sensors 28. Frames 12, with the electromechanical transducers 14 thereon, are

deployable underground so that the transducers are disposed in an array which has at least two

dimensions. An a-c current or ultrasonic signal generator 30 is operatively connected to

elecfroacoustic transducers 26 for energizing the elecfroacoustic transducers with electrical

signals of one or more pre-established ultrasonic frequencies. So energized, the

electroacoustic transducers 26 produce ultrasonic pressure waves in the underground

formations or structures 22 in which the respective frames or carriers 12 are disposed.

In order to make use of the ultrasonic signal information obtained by sensors or

electromagnetic fransducers 14, the relative positions of the sensors must be known. Pursuant

to one methodology, frames 12 are deployed at predetermined positions and at pre-established

angles relative to ground surface 24. Accordingly, because the locations of the transducers 14

on frames 12 are known, the underground locations of the sensors relative to one another will

be known. Alternatively, a position determination circuit 32 (Fig. 3) is operatively connected

to sensors or elecfromechanical transducers 14 for determining locations of the sensors

relative to one another.

After being reflected or echoed by underground surfaces, where there is a change in

the rate of transmission or conduction of the pressure waves, the pressure waves are detected

by acoustoelectric sensors 28. Sensors 28 generate electrical signals having frequencies

corresponding to those of the incoming pressure waves. The electrical signals are transmitted

via a multiplexer or switching circuit 33 to an analog-to-digital converter 34 into digital signals which are temporarily stored in a buffer 36 for timely analysis by a preliminary signal

processing circuit or ulfrasonic wave analyzer 38. Wave analyzer 38 includes position

determination circuit 32 (Fig. 3) and a time base 40.

Circuit 32 receives, via a lead or multiple 41 extending from analog-to-digital

converter 34 and buffer 36, electrical signals derived from incoming pressure waves. Circuit

32 separates out those signals corresponding to direct or unreflected ultrasonic pressure wave

transmission paths to determine the relative locations of sensors or transducers 14 (both

elecfroacoustic fransducers 26 and acoustoelectric sensors 28). The encoded locations of

fransducers 14 are communicated by circuit 32 to a surfaces detector module 42. Module 42

analyzes incoming electrical signals from sensors 28 to determine and analytically define the

surfaces of an underground object UO which generate reflected or echoed pressure waves in

response to ultrasonic pressure waves from fransducers 26. Time base 40 enables operation of

circuit 32 and module 42.

As illustrated in Fig. 1, module 42 is connected at an output to an object construction

module 44 which analyzes the surface information from module 42 to determine whether a

collection of detected surfaces fit together to form an object. Module 44 thus determines the

three-dimensional shapes of the underground object UO. Module 44 is connected at outputs

to a video signal generator 46 which produces, from the object information from module 44,

an image of underground object UO. The image is varied by generator 46 in accordance with

instructions from a view selector module 48 and a surface filter module 50. In response to

commands from an input device 52 such as a keyboard or a mouse, view selector 48 provides

instructions to video signal generator 46 as to the angle and magnification of the image

encoded in the video signal. In response to additional commands from input device 52, filter module 50 instructs video signal generator 46 to remove one or more surfaces from the image

of underground object UO, thereby enabling the inclusion in the image of objects inside of or

behind object UO.

Object construction module 44 is also connected at an output to an object identifier

circuit 54 which consults a memory 56 in a pattern recognition or comparison operation to

determine the identity or object type of underground object UO. If an identification is

established, object identifier circuit 54 provides instructions to video signal generator for

incorporating identification information into the video signal. The identification information

may include words or symbols providing a name and known historical data pertaining to the

class of objects into which object UO is determined to fall.

Generator 46 is connected to a video monitor 58 for displaying the view-selected and

surface-filtered image of underground object UO, together with any ancillary information

discovered by object identifier circuit 54.

Preliminary signal processing circuit or wave analyzer 38 is operatively connected to

a-c current or ultrasonic signal generator 30 via an outgoing signal control unit 60. Control

unit 60 produces a confrol signal which determines, for example, the frequency of an outgoing

ultrasonic pressure wave produced by electroacoustic fransducers 26 and the identity of the

particular elecfroacoustic fransducer 28 generating that pressure wave. Signal generator 30 is

a variable-frequency ultrasonic signal source and is connected to electroacoustic transducers

26 via a multiplexer or switching circuit 62. Signal generator 30 and switching circuit 62

receive control signals via respective leads 64 and 66 from control unit 60. Switching circuit

62 operates to connect signal generator 30 sequentially to different electroacoustic fransducers

26. Typically, the energization sequence of transducers 26 is pre-established and determined in part by the specific configurations of transducers 26 and sensors 28 on frames 12.

Similarly, control unit 60 is connected to multiplexer or switching circuit 33 via a lead

or multiple 68 for inducing that circuit to sequentially connect analog-to-digital converter 36

to different acoustoelectric sensors 28. The connection sequence of sensors 28 is also pre-

established and determined in part by the specific configurations of fransducers 26 and sensors

28 on frames 12.

In many cases, in order to facilitate the separation of incoming reflected signals

originating at different electroacoustic fransducers 26, these transducers are activated with

signals of detectably different ultrasonic frequencies. The sequence of fransducer activation

and the frequency or frequencies of actuation are communicated by control unit 60 to surfaces

detector module 42. Detector module 42 utilizes that information to properly analyze the

arriving ultrasonic signals. In the event that the incoming data are insufficient for detector

module 42 to isolate, calculate and define surfaces of underground object UO, the detector

module may transmit a signal to confrol unit 60 to change the energization sequence of

fransducers 26 and/or the energization frequencies.

As illustrated in Fig. 2, frames 12 may be inserted into ground formations or

underground structures 22 in substantial parallelism with a local gravity vector G or,

alternatively, at an angle to that vector, as indicated in phantom lines 70.

Figs. 4 and 5 depict alternative frames or transducer carriers 72 and 74. These

alternative frames are provided with sharp end points 73 and 75 for facilitating the insertion of

the frames through a ground surface (24 in Fig. 2). As described hereinabove with reference

to Fig. 1, frames 72 and 74 carry electromechanical fransducers 76 and 78 which include

electroacoustic transducers (not separately designated) for generating outgoing pressure waves and acoustoelectric sensors (not individually labeled) for detecting incoming reflected or

refracted pressure waves.

It is to be noted that the connections of transducers 26 and sensors 28 to switching

circuits 62 and 33 may be implemented via wireless communications links or via wires.

Fig. 6 shows a specific configuration of an underground-topography imaging system

including just one electroacoustic fransducer 26 and a multiplicity of acoustoelectric sensors

28. Here the enhancement of image resolution and optimization of surface detection and

definition are accomplished mainly by varying the ulfrasonic output frequency of the one

electroacoustic transducer and the sequence of signal transmission from acoustoelectric

sensors 28.

Fig. 7 depicts a particular configuration of another underground-topography imaging

system including just multiple electroacoustic transducers 26 and a single acoustoelectric

sensor or fransducer 28. In this case, the enhancement of image resolution and optimization

of surface detection and definition are accomplished by varying the ultrasonic output

frequencies and the energization sequence of the electroacoustic transducers.

As illustrated in Fig. 8, another system for conducting an underground survey

comprises a liquid filled receptacle 80 disposable on a ground surface 82. Generally, the

receptacle is disposed on the ground surface prior to being filled with liquid such as water

from a supply 84. Supply 84 is connected to an inlet port 86 of receptacle 80. A valve (not

shown) may be provided for regulating liquid flow to and from receptacle 80.

Receptacle 80 may take the form of a rubber or polymeric bag which may have a

single internal chamber (not shown) or multiple internal chambers separated by partitions (not shown). In a specific variation of the receptacle 80, an upper wall (not separately designated) of the receptacle is a rigid panel while the other walls of the receptacle are flexible, thereby

permitting a conforming of the bag to a ground surface. This variation with its rigid upper

panel, or any other variation where receptacle has a substantially rigid frame or support

structure, facilitates transport and relocation of the receptacle, for instance, by a helicopter, a

crane, a forklift, etc.

Disposed on or inside receptacle 80 are a plurality of electromechanical fransducers 88

including one or more electroacoustic transducers 90 and one or more acoustoelectric sensors

92. Electronic circuit functional block components of the embodiment of Fig. 8 are the same

as in the embodiment of Fig. 1 and carry the same reference numerals. Thus, elecfroacoustic

fransducers 90 are operatively connected in a predetermined sequence to signal generator 30

via multiplexer or switching circuit 62 under the control of unit 60. Acoustoelectric sensors

92 are connected to wave analyzer 38 via switching circuit 33, analog-to-digital converter 34 and buffer 36. The digitized reflected pressure wave signals are processed by analyzer 38,

surfaces detector module 42, object construction module 44, and object identifier 54 as

discussed above with reference to Fig. 1. These circuit components, together with video

signal generator 46, view selector module 48, filter module 50 and outgoiηg signal control

unit 60, may be implemented as generic computer circuits modified by special purpose

programming. Reference numeral 94 designates a computer.

As discussed above with reference to Figs. 1 and 2, ground surface 82, as well as

underlying subsurface structures (see Fig. 2), may be wetted to facilitate the conduction of

ultrasonic pressure waves. To that end, receptacle 80 may be provided in a lower surface with

apertures 96 for enabling the passage of liquid from the receptacle onto ground surface 82 and into the underlying subsurface structures. Of course, this technique will be applicable only if the underlying surfaces are capable of absorbing the liquid.

It is to be noted that the transducer-carrying frames 12 of Figs. 1 and 2, as well as the

receptacle 80 of Fig. 8, may be used where acoustic or pressure waves are generated by a

source other than a fransducer, for example, an explosive charge. To that end, a number of

frames 12 in the embodiment of Fig. 1 may be provided with explosive charges. To compute

effectively exact locations of the explosive charges relative to the acoustoelectric sensors 28

and of the acoustoelectric charges relative to each other, the explosive charges may be

provided in pairs, with a first charge being detonated to enable automatic determination of the

relative positions of the explosive charges and the acoustoelectric fransducers. The second

charge of each pair is then deployed in the same location as the respective detonated charge

and subsequently detonated to generate acoustic or pressure waves of different frequencies in

the underground structures or formations. The explosive charges used in this process are of

substantially less power than the charges used in oil and seismic exploration inasmuch as the

depths of underground searching for buried artifacts and other articles of manufacture are

generally substantially less than the search depths for oil and gas deposits.

Fig. 9 illustrates a frame or carrier in the form of a net 98 to which a plurality of

electromechanical transducers 100 are attached. Transducers 100 include one or more

acoustoelectric sensors (not separately designated) and optionally includes one or more

electroacoustic fransducers (not separately designated). Transducers 100 are adapted for

placement in pressure- wave-transmitting contact with a ground surface 102. The exact design

of the fransducers depends on the type (frequency) of pressure waves being used in the

surveying process. The type of pressure waves in turn depends in part on the nature of the

underground structures or formations below surface 102 and on the nature of surface 102. Higher frequencies (e.g., ultrasonic) may be transmitted through wet land structures than

through dry land structures (rock).

Fig. 10 depicts a carrier pad 104 to which a plurality of elecfromechanical transducers

106 are attached. Pad 104 may be used with the circuitry illustrated, for example, in Fig. 8, to

determine the locations, shapes, contents, and identities of objects buried underground. It is to

be noted that in many cases, the frequencies of emitted pressure waves are most effectively

distributed through a range of sonic frequencies. Of course, because resolution capability of a

scanning or search process is dependent on the frequencies being used, a range of frequencies

are suggested where the sizes of possible buried objects vary dramatically.

Where ultrasonic frequencies are used, it is advantageous in many instances if the

ground structure being surveyed is wet, such as clay or marshland. A ground structure may be

infused with water to produce a desirable degree of wetness.

Fig. 11 shows a wedge-shaped frame 108 having a lower wall 110 and an upper wall

112 disposed at an angle relative to one another. Frame 108 may be a balloon or container

which is expandable into the illustrated configuration upon being filled via a port 114 with a

liquid such as water. As shown in Fig. 12, a plurality of expanded frames 108 are disposed in

a predetermined configuration such as a circle, with a plurality of pads 104 being disposed on

the upper walls 112 of frames 108 in pressure- wave-transmitting contact therewith. Pads 104

are effectively part of upper walls 112.

In an alternative pressure-wave transmission assembly, a plurality of collapsible

containers or balloons 116 (Fig. 13) each having an arcuate configuration in an expanded

condition (Fig. 14) are placed side by side to form a circle (Fig. 15). Each container or

balloon 116 has an upper wall 118 and a lower wall 120 oriented at a wedge angle to one another in the expanded condition of the respective balloon or container. Each container or

balloon 116 is provided on upper wall 118 with a plurality of electromechanical transducers

122 in a pre-established array.

The underground surveying equipment of Figs. 10-12 and Figs. 13-15 are disposed at

a site above buried treasure or other artifacts of value. The circular configurations are

intended to surround the suspected site to facilitate the derivation or generation of reflected or

echoed sonic or ulfrasonic signals.

The underground surveying equipment of Figs. 10-12 and Figs. 13-15 may use

ultrasonic pressure waves to detect underground objects and the surfaces of those objects, as

discussed above with reference to Figs. 1 and 8. In another alternative technique, the pressure

waves are sonic waves of controlled frequencies generated by transducers. Alternatively, the

underground pressure waves may be generated by explosive devices. For example, an

explosive device might be implanted below the surface within the circular configuration of

Fig. 12 or 15. Where an explosive device is used, the pressure waves generated by the

explosive device must be computer analyzed with Fourier transforms or other wave-

deconstructing algorithms to determine the frequency spread of the pressure waves generated

by the particular explosion. The wave analysis of incoming reflected waves is then carried

out based on the computed outgoing wave packet. Of course, the pressure waves generated by

an explosive device will include sonic frequencies as well as ulfrasonic and subsonic

frequencies.

Fig. 16 illustrates a hand-held or hand-manipulable device for conducting underground

searches. A shaft 124 is provided at a lower end with a frame 126 carrying an array of

elecfromechanical pressure-wave transducers 128 (Fig. 17). As shown in Fig. 18, a flexible pad 130 filled with water or other liquid is attachable to the bottom side of frame 126 for

enhancing the conduction of pressure waves to and/or from transducers 128. At an upper end,

shaft 124 is provided with a handle 130 and a video display 132. Alternative configurations

of frame 126 are illustrated in Figs. 19 and 20. In Fig. 19, a frame or transducer carrier

component 134 has a pyramidal or conical shape and is provided along sloped sides 136 with

an array of electromechanical transducers 138. A water filled pad 140 may be provided along

a bottom end of frame or carrier component 134. In Fig. 20, a frame or carrier 142 is ring

shaped and has fransducers 144.

As illustrated in Fig. 21, a rigid frame 146 carrying a plurality of electromechanical

fransducers 148 is mounted to a land vehicle 150 via a pair of rigid arms 152 and a cable 154

connected at one end to vehicle 150 and at an opposite end to a pyramidal trusswork 156 rigid

with frame 146. Transducers 148 are operatively connected to signal generating components

and signal analyzing components as discussed hereinabove with reference to Figs. 1 and 8.

The pressure waves generated by fransducers 148 may include sonic frequencies, as well as

ultrasonic frequencies. Several different frequencies may be generated simultaneously for

produced pressure waves of the same multiple frequencies. Reflected waves are separated by

filters (not shown) and analyzed separately. Alternatively, or additionally, the different

frequencies may be produced in seriatim.

The apparatus of Fig. 21 is especially suited to detecting land mines along a road. A

pair of frames 146 (only one illustrated) may be mounted to opposite sides of vehicle 150 for

searching a two dimensional area such as a field or a yard. Every other pass of vehicle 150 in

a snaking search pattern utilizes the frame on the same side of the vehicle. Thus, the frames

alternate from pass to pass. When a land mine is detected using the apparatus of Fig. 21 , a marker is planted at the

site of the detected mine. The mine is subsequently detonated by designated personnel.

Vehicle 150 may take a path around the detected land mine to continue the search along the

subject road. Alternatively, vehicle 150 may reverse itself to await destruction of the detected

mine. In a modified procedure, vehicle 150 may be used itself to deposit an explosive device

proximately to the detected mine. The explosive device is detonated by remote control, once

vehicle 150 has removed itself to a safe location.

Arms 152 may be pivotably mounted to frame 146 and vehicle 150 for purposes of

enabling a variation in the height of frame 146 above a road surface. Drives (not shown) may

be connected to arms 152, as well as to cable 154 for purposes of automatically changing the

height of frame 146.

Another way of moving a rigid frame 158 above a ground surface such as a road RD is

depicted in Fig. 22. Frame 158 is suspended by cables 160 from a helium-filled balloon 162.

Frame 158 and/or balloon 162 is provided with motors 164 and propellers 166 for changing

the position of frame 158 relative to ground or road surface RD. Preferably, motors 164 are

remotely connected by a computer 168 transmitting instructions and control signals via a

wireless transceiver 170. Conventional means (not shown), wirelessly controlled by computer

168, for elevating or lowering balloon 162 and frame 158 may also be provided.

Frame 158 carries a plurality of elecfromechanical transducers 172 for generating

outgoing pressure waves of different frequencies and for detecting incoming pressure waves

reflected by underground surfaces in response to the outgoing pressure waves. Signal

generators for energizing the outgoing wave generators may be mounted to frame 158 and

controlled by instructions from computer 168 transmitted wirelessly over transceiver 170. In response to the incoming pressure waves, sensors among fransducers 172 produce analog

signals which may be transmitted (after proper modulation) to computer 168 via transceiver

170. Alternatively, some signal processing of the analog signals may be performed on frame

158. In yet another alternative configuration of the system of Fig. 22, computer 168 may be

located on frame 158. In that case, transceiver 170 is used to fransmit instructions from an

operator to the on-board computer and to relay, from the on-board computer to a monitor, a

video signal encoding images of underground objects.

As discussed above with reference to Figs. 1 and 8, object identifier 54 may be used to

identify different types of land mines. To that end, memory 56 stores shape and size

specifications of known types of land mines. Memory 56 may additionally store ancillary

information such as operating specifications and deactivating sequences of the various known

types of land mines, if available. Accordingly, in some cases, detected land mines may be

deactivated and subsequently disassembled, rather than detonated.

Scanning systems as described herein for detecting and identifying underground

objects are capable of determining positions of detected underground objects with respect to a

given reference point. The determined coordinates may be used as markers for enabling

subsequent visits to the locations of the detected objects, for instance, with the aim of digging

up the objects, in the case of buried artifacts of value, or destroying the objects, in the case of

land mines. Markers may also be physical indicators deposited on a ground surface for

identifying the locations and/or natures of detected objects which are underground.

Fig. 23 illustrates an alternative transport vehicle 174 in the form of a remote-

controlled airplane. A framework 176 carrying transducers 178 is suspended by cables 180

from plane 174. Fig. 24 depicts a scanning system wherein a frame 182 is suspended by cables 184 from a helicopter 186. Transducers 188 are mounted to frame 182.

As shown in Fig. 25, an alternative technique for detecting underground objects

utilizes a pad 190 to which a plurality of electromechanical transducers 192 are attached. A

remote-controlled robot 194 such as a miniature all-terrain vehicle is attached to one end of

the pad for dragging the pad along a ground surface. Where the detection of land mines is

intended, it is contemplated that robot 194 and pad 190 are sufficiently light weight to avoid

mine detonation when the robot and the pad move over land mines. Pad 190 may be stored in

a coiled configuration inside a container. Robot 194 may be used to remove pad 190 from

such a container, for example, by pulling and unrolling the pad at the onset of a scanning

operation.

It is to be noted that fransducers 192 have a density or spacing which facilitates

detection of objects of an intended group. Thus, to detect land mines, which are typically

located within two feet of the surface, the fransducers have a density greater than that

necessary to detect buried archeological ruins. Transducers 192 are energizable with

alternating electrical waveforms of different frequencies, for purposes of facilitating soil

penetration and surface detection.

Fig. 26 shows a flexible pad 196 which is stored in a wound-up configuration (not

shown) inside a container 198. Pad 196 carries a plurality of electromechanical transducers

200 (such as speakers and microphone sensors) in a predetermined array. In order to place

pad 196 over a ground surface harboring suspected land mines, a rod 202 may be used to

grasp or hook a leading edge 204 of pad 196 and pull the pad out of storage container 198.

Rod 202 is further used to position pad 196 over a selected ground surface area.

Thus, it is clear that a flexible transducer-carrying pad as discussed hereinabove with reference to Figs. 10, 25 and 26 may be pushed or pulled over a ground surface. Markers (not

shown) may be left on the ground surface to indicate the locations of detected land mines.

Where an air-borne vehicle such as balloon 162, plane 174 or helicopter 186 is used, markers

may be dropped from the vehicle. Alternatively, input from the surface scanning may be used

to identify pre-existing surface markers or reference points. The locations of detected mines

relative to the selected pre-existing reference points are calculated by the wave-analyzing

computer and stored for future use in destroying detected land mines.

As illustrated in Fig. 27, a carrier 206 for electromechanical transducers 208 may

comprise a rigid panel 210 attached to an upper side or forming an upper wall of a flexible

bag 212. Bag 212 may be filled with a fluid medium such as gel or water for purposes of

enhancing pressure wave transmission to and from an uneven ground surface. Carrier 206 is

placed in position by a crane 214.

Various safety feature may be incorporated into a land mine detection system as

described hereinabove, particularly where the carrier vehicle is manned. For example, with

reference to Fig. 21, an automatic engine or transmission shut-off may be provided for

immediately ceasing forward motion of vehicle 162 if a land mine is detected. This feature is

especially advantageous where the vehicle moves continuously during a scanning operation,

rather than intermittently.

As illustrated in Fig. 28, a system for surveying an underwater topography comprises

an ultrasonic sensor array 312 disposable in physical contact with a body of water BW. The

sensor array generates electrical signals encoding ulfrasonic echo responses of underwater

objects UO in the body of water BW. Sensor array 312 includes a plurality of

electromechanical fransducers 314 exemplarily realized essentially by piezoelectric wafers. Sensor array 312 further includes a carrier 316 such as a net. Carrier net 316 is towed through

water body BW by a boat BT via a tow line 318. A multiple lead cable or wireless

telecommunications link 320 extends along tow line 318 and operatively connects transducers

14 to a processing system 322. Processing system 322 analyzes incoming electrical ulfrasonic

signals arriving from transducers 314 and generates a video signal encoding an image of an

underwater topography including one or more of the underwater objects UO. The video

signal is fed to a monitor 346 for display of the image thereon.

Sensor array 312 and more particularly selected transducers 314 produce mechanical

pressure waves 324 of one or more ultrasonic frequencies. These outgoing pressure waves

324 are reflected from the underwater objects UO, as indicated at 326, and received by

fransducers 314. The incoming pressure waves are converted by selected transducers of

sensor array 312 into electrical signals transmitted over cable or wireless telecommunications

link 320 to processing system 322.

In order to optimize data production, fransducers are disposed in a configuration

extending in at least two dimensions. This configuration is determined in part by the

attachment of transducers 314 to carrier net 316.

As illustrated in Fig. 29, transducers 314 include a plurality of pressure-wave-

generating elecfroacoustic transducers 328 and a plurality of pressure- wave-receiving

acoustoelectric fransducers or sensors 330. Transducers or wave generators 328 are arranged

in a predetermined two- or three-dimensional configuration such as a V. Transducers or

sensors 330 also have a two- or three-dimensional configuration.

An a-c current or waveform generator 332 is operatively connected to electroacoustic

transducers 328 for energizing the electroacoustic transducers 328 with an electrical signal of a pre-established ultrasonic frequency. Elecfroacoustic fransducers or wave generators 328

are energized one at a time, in a predetermined sequence, by the same ulfrasonic frequency or

by different ultrasonic frequencies.

Acoustoelectric transducers or sensors 330 are operatively connected via cable or

wireless telecommunications link 320 and an analog-to-digital converter 336 to a digital

processor 334 . Processor 334 may be implemented by a general purpose computer specially

programmed to realize the functional modules shown in Fig. 28. Processor 334 includes, as

one such module, a preliminary signal processing circuit 338 which analyzes incoming

pressure waves 326 in accordance with the location of the particular elecfroacoustic transducer

328 which generated the outgoing pressure wave 324 reflected by the underwater objects UO

to produce the incoming pressure waves 326.

As illustrated in Fig. 30, preliminary signal processing circuit 338 includes a circuit

340 for determining the positions of transducers 14 relative to one another. Circuit 340

receives, via a lead or multiple 341 extending from analog-to-digital converter 336, electrical

signals derived from the incoming pressure waves 326. Circuit 340 separates out those

signals corresponding to direct or unreflected ulfrasonic pressure wave transmission paths to

determine the relative locations of transducers 314. The encoded locations of transducers 314

are communicated by circuit 340 to a surfaces detection circuit 342. Circuit 342 analyzes

incoming electrical signals from sensor array 312 to determine and analytically define the

surfaces of underwater objects UO which generate reflected pressure waves 326 in response to

ulfrasonic pressure waves 324 (Fig. 28). Circuit 342 determines the three-dimensional shapes

of the underwater objects UO. A time base 343 enables operation of circuits 340 and 342.

As shown in Fig. 29, preliminary signal processing circuit 338 is operatively connected to a video signal generator 344. Partially in response to surface data from circuit

338, generator 344 produces a video signal encoding an image of an underwater topography

including selected underwater objects UO. Generator 344 is connected to video monitor 46

for displaying the underwater image.

Preliminary signal processing circuit 338 is operatively connected to waveform

generator 332 via an outgoing signal control unit 348. Control unit 348 produces a control

signal which determines, for example, the frequency of an outgoing ultrasonic pressure wave

24 and the identity of the electroacoustic fransducer 328 generating that pressure wave.

Waveform generator 332 comprises a variable- frequency ultrasonic signal source 350 and a

multiplexer 352, as illustrated in Fig. 31. Source 350 and multiplexer 352 receive confrol

signals via respective leads 354 and 356 from confrol unit 348. Multiplexer 352 operates to

connect signal source 350 sequentially to different electroacoustic transducers 328. Typically,

the energization sequence of transducers 328 is pre-established and determined in part by the

specific configurations of fransducers 328 and transducers 330 on carrier 316. In many cases,

in order to facilitate the separation of incoming reflected signals 326 originating at different

electroacoustic fransducers 328, these fransducers are sensitive or responsive to signals of

detectably different ultrasonic frequencies. The sequence of transducer activation and the

frequency or frequencies of actuation are communicated by control unit 348 to surfaces

detection circuit 342. Detection circuit 342 utilizes that information to properly analyze the

arriving ultrasonic signals. In the event that the incoming data is insufficient for detection

circuit 342 to isolate, calculate and define surfaces of underwater objects UO, the detection

circuit may transmit a signal to control unit 348 to change the energization sequence of

fransducers 328 and/or the energization frequencies. As illustrated in Fig. 32, analog-to-digital converter 336 includes a multiplexer 358

and digitization elements 360. Multiplexer 358 receives a switching confrol signal via a lead

362 extending from confrol unit 348. Control unit 348 enables the decoding of incoming

ultrasonic pressure waves in a pre-established sequence. This sequence is determined in part

by the configurations of transducers 328 and 330 and by the frequencies of energization. In

addition, surfaces detection circuit 342 (Fig. 30) may cause confrol unit 348 to vary the signal

reception sequence for purposes of enhancing resolution and surface detection.

Fig. 33 shows a specific configuration of an underwater-topography imaging system

including just one electroacoustic fransducer 364 and a multiplicity of acoustoelectric

transducers 366. Here the enhancement of image resolution and optimization of surface

detection and definition are accomplished mainly by varying the ulfrasonic output frequency

of the one elecfroacoustic transducer and the sequence of signal transmission from sensors or

acoustoelectric transducers 330.

Fig. 34 depicts a particular configuration of another underwater-topography imaging

system including just multiple elecfroacoustic transducers 368 and a single acoustoelectric

fransducer 369. In this case, the enhancement of image resolution and optimization of surface

detection and definition are accomplished by varying the ultrasonic output frequencies and the

energization sequence of the electroacoustic transducers.

As shown in Fig. 35, an ultrasonic pressure wave generating and/or sensing unit 370

attachable, for instance, to a junction of different sfrands of carrier net 316 comprises a body

or casing 372 and a plurality of tubular directional elements 374 projecting in different

directions from body 372. Each element 374 is associated with a respective piezoelectric

wafer or chip (not illustrated). Thus, a single location on carrier net 316 may support a plurality of elecfroacoustic fransducers 328 and/or acoustoelectric fransducers 330. However,

there must be a plurality of locations on carrier net 316 which carry one or more ultrasonic

pressure wave transducers 314.

As depicted in Fig. 36, a carrier net 376 for an ulfrasonic sensor array 378 may be

provided with a plurality of self-contained motive or propeller units 380. Units 380 are

connected to net 376 via tension lines 382 and have steering vanes 384, as well as propellers

386. Steering vanes 384 and propellers 386 may be controlled from a remote location, for

example, a ship (not shown) either via a signal transmission cable (not shown) or via wireless

signal transmitters and receivers (not shown).

Propeller units 380 are attached to carrier net 376 for applying a force thereto relative

to a body of water in which or one which carrier net 376 is disposed. It is contemplated that

an underwater disposition of carrier net 376, for example, below any surface wave action,

would be optimal for reducing stress on the carrier and for facilitating the maintenance of the

sensor array 378 in a given configuration. The orientations of propeller units 380 relative to

carrier net 376 will change, as indicated in phantom lines at 388, to lift carrier net 376 towards

the surface of a body of water after completion of a maritime scanning operation. It is to be

noted that propeller units 380 can be differentially operated to translate carrier net 376 and the

entrained sensor array 378 in different directions, including up and down and parallel to an

underlying underwater geologic surface. The orientation of carrier net 376 in a body of water

may be changed to facilitate scanning and object detection operations.

Fig. 37 depicts a carrier 390 of rigid frame construction. Fastened to carrier 390 are a

plurality of ulfrasonic pressure wave generating and/or sensing units 392. Carrier 390 may be

dragged along a water surface or beneath the surface by a dedicated propeller unit 394. Auxiliary propeller units 396 may be tethered to carrier 390 for assisting the main propeller

unit 94 in orienting the carrier and in raising and lowering the carrier through a body of water.

As discussed above, ultrasonic pressure wave generating and/or sensing units 392 are

operatively connected to a processing system 322 (Fig. 28) via a cable or wireless fransceiver

components. In the embodiment of Fig. 37, the determination of fransducer position may be

implemented simply and automatically by virtue of fixation of the locations of the

electromechanical transducers 392 relative to one another.

Fig. 38 illustrates another fransducer carrier 406 of substantially rigid construction.

Carrier 406 includes a substantially cylindrical body 408 with a pair of stabilizers 410 and

412. Stabilizers 410 and 412 may be shiftable relative to body 408, by respective motors (not

illustrated), for facilitating the steering of carrier 106 through a body of water WB. Carrier

406 is dragged through the water by a tension line 414 connected to a back end of a surface

vessel 416.

An array of elecfromechanical (elecfroacoustic and acoustoelectric) transducers 418

are mounted to carrier body 416 and optionally stabilizers 410 and 412 for picking up

reflected pressure waves of ultrasonic frequencies from underwater surfaces. A signal

transmission line (not separately illustrated) extending along tension line 414 or a wireless

transmission link may be provided for carrying signals between transducers 418 and vessel

416. If carrier 406 is provided with motors for shifting stabilizers 410 and 412, control

signals for those motors may also be carried by this transmission line.

Carrier body 408 may be enclosed and define one or more internal chambers. For

example, carrier body 408 may itself be a personnel-carrying submarine. In that event, a

propeller 420 is located at the rear end of the carrier body 408. As illustrated in Fig. 29, processor 334 includes a view selector module 398 which is

operatively connected to video monitor 346 for selecting a displayed image from among a

multiplicity of possible images of underwater objects UO. More specifically, view selector

module 398 operates in response to instructions from a keyboard 400 or a mouse 402 to select

a view angle and a magnification for the displayed image. Accordingly, a user may induce a

change in the displayed image from one view angle to another or from one magnification to

another.

As further illustrated in Fig. 29, processor 334 includes a filter stage or object removal

module 404 operatively connected to video monitor 346 for eliminating a selected object or

portion of an object from the displayed image. Modules 398 and 404 are incorporated into

processor 334 and are realized by generic computer circuits whose functions are determined

by programming.

In surveying an underwater topography utilizing an imaging system as described

herein above, for instance, with reference to Fig. 28, the sensor array is disposed in operative

contact with body of water BW, determining physical locations of the transducers relative to

to a multiplicity of pressure wave paths from the transducers to each of the objects and back to

the fransducers. The electrical signals are automatically analyzed to generate a video signal

encoding an image of the objects, the video signal being fed to a video monitor to thereby

display the objects on the monitor.

Fig. 39 illustrates all of the elements shown in Fig. 29 and shows additional

components of processing system 322 and digital processor 334. In particular, a pattern recognition circuit or module 422 is operatively connected to preliminary signal processing

circuit 338 for purposes automatically analyzing the surface data from circuit 338 to identify

types of objects located underwater. Pattern recognition circuit 422 consults a memory 424

which is loaded with data describing the shapes of objects of various classes. The contents of

memory 424 may vary, depending on the purposes of underwater searching. For example,

where the imaging system is used for antiquities hunting, memory 424 contains encoded

templates for ancient ships, columns, urns, statuary, and other objects known to be frequently

transported via sea going vessels. Where the imaging system is used for applications in

marine biology, memory 424 contains three-dimensional surface data describing the shapes of

different underwater life forms, which may include fish, mammals, crustaceans, jellyfish,

squid, etc. In any case, where images of underwater target objects are to be shown on video

monitor 346, object removal module 404 filters out those objects which are not selected as

being of interest. Object removal module 404 may also consult memory 424, either directly

or indirectly via pattern recognition circuit 422, to determine which objects are to be displayed

and which objects are to be deleted from representation on video monitor 346. Of course,

input devices such as keyboard 400 may be operatively connected to pattern recognition

circuit 422 for purposes of enabling user selection of object classes of interest during any

particular ulfrasonic underwater search.

Processor 334 further includes a module 426 for determining a location relative to

global coordinates (latitude, longitude, and sea or ocean depth). This module receives input

from conventional electronic navigation equipment (not illustrated). Coordinates module 426

and pattern recognition circuit 422 are connected to a storage or recording device 428 such as

a printer and/or to memory 424 for purposes of recording the identity and location of any objects detected by pattern recognition circuit 422. Thus, a sensor carrier 316, 376, 390, 406

may move along a search path while continually monitoring underwater objects and

maintaining a log of detected objects. Subsequently, a manned or robotic vessel may be

dispatched to more closely inspect any located objects of interest.

In an alternative search mode, pattern recognition circuit 422 is connected to motors

430 which propel the sensor carrier 316, 376, 390, 406. Upon detecting an object of possible

interest, pattern recognition circuit 422 de-energizes motors 430, thereby maintaining the

sensor carrier in proximity to the objects while a closer or more complete investigation is

undertaken.

It is to be noted that an ultrasonic transducer carrier 316, 376, 390, 406 as described

herein may be provided with various devices for protecting the sensor array from marine

creatures such as dolphins or sharks. Such protective devices could include chemical

dispensers for releasing repellants into the water. The ultrasonic pressure waves may in

themselves have a repellant effect, as with land animals such as rodents.

Sensor carriers 316, 376, 390, 406 may take various forms and shapes and may be

provided with various ancillary devices such as video cameras, manipulating arms, storage

compartments for objects retrieved by such arms. Where the carrier is provided with

dedicated motors, processor 334 may be provided with programs for filtering out ulfrasonic

vibrations arising from the operation of the motors.

An underwater imaging system as described hereinabove may be supplemented by an

acoustic lens (not illustrated) disposed between the sensor array and the underwater surfaces

under inspection. A focusing acoustic lens may be formed by a lenticular volume with a

velocity of sound slower than that of a surrounding medium, in analogy with optical lens. In the case of sea water or marine environments, a medium with a lower velocity of sound, but

not one discrepant enough to cause a serious impedance mismatch and resultant signal loss, is

conveniently provided by fresh water. The fresh water may be held in shape by a polymeric

sack or plastic bag. The bag is filled under sufficient pressure to minimize rippling and

sloshing at the bag - sea water interface, which would cause image distortion. Ripples

significantly below an acoustic wavelength in size are acceptable. The material of the bag

itself is chose to be tough and strong, yet thin enough so that its acoustic impedance is

irrelevant. The bag may be advantageously strengthened by tensile fibers, and also provided

with rigid ribs to assist in holding a lenticular shape. The lenticular shape may be the

underwater optical equivalent of a Fresnel lens.

In operation the bag of the acoustic lens is attached to a rigid frame, which holds an

acoustic sensor array at a fixed stand-off distance and orientation with respect to the sensor

array. Of course, imaging software is modified to take the lens into account. In some cases

where an acoustic lens is used, the sensor array functions like the photo-electric sensor array

of a digital camera, or the human retina, receiving an ordinary image. The region between the

sensor array and the bag is advantageously baffled from stray sound, analogous to light

exclusion means in a camera, and the assemblage may be provided with acoustic "spotlight."

The spotlight may be a broadband or narrow band acoustic source, advantageously adjustable

in frequency output to maximize resolution in a given situation. Given broadband acoustic

illumination, reflectance at different frequencies may be encoded in color at an output display,

utilizing another channel of perceptual information. By varying the frequency profile of the

"spotlight," and the range of frequencies color encoded in a display, a skilled operator may

investigate an underwater scene in a variety of frequency bands efficiently and intuitively, finding the band offering greatest penetration and resolution in a given context. The

experienced operator may also become acquainted with the "color" and appearance of various

acoustic objects he may search for on a regular basis, e.g. a particular kind of archeological

artifact or an underwater pipeline, and thereby increase search efficiency.

As a further elaboration of this embodiment, a pair of such sensor systems may be

provided, advantageously mounted in fixed geometric relation on a tethered and controllable

submersible, or possibly a manned underwater vehicle. Perceptual skills of the experienced

operator will now include stereoscopic perception of depth (i.e., range) information, as well as

the ability to 'take a look around' a target area while building up a mental conception of it,

inspecting areas of special ambiguity and interest from different angles and with varying

illumination frequencies.

It is to be noted that in general, in an underground or underwater imaging system as

described herein, two sensor arrays spaced from one another along a baseline may provide

separate image data streams for forming two images of the same objects from different angles.

These two angularly differentiated images may be provided to respective eyes of a human

operator by conventional stereoscopic techniques so as to provide the operator with

stereoscopic vision. For instance, a human operator may be given access to stereoscopic

image fields transmitted from the two sensor arrays and viewed through stereoscopic goggles.

Coupled with the ability to steer and reposition a tethered submersible, for example, this gives

an operator the ability to 'see' underwater acoustically, and to use the native binocular image

processing ability of the human brain to build up a model of a three-dimensional structure.

It is to be additionally noted that the two sensor arrays in a stereoscopic imaging

system may be composed of different collections of sensors disposed on the same rigid frame. In that case, there may be some overlap not only in the areas occupied by the two sensor

arrays on the frame but also overlap in the specific sensors so that some sensors are used in

each array. It is only necessary that the two collections of sensors include some different

sensors to provide a baseline to establish different angular views.

Another technique for enhancing data collection and image formation is the use of

phased sensor arrays. In accordance with known phased array techniques, the phases of

outgoing acoustic pressure waves, as well as the locations of the transducers producing those

waves, may be varied to effectively simulate a change in physical orientation of a sensor

array, including an array defined as a subset of all sensors on a rigid frame. In accordance

with known phased array techniques, phase is also be taken into account in the analysis of

incoming acoustic or ulfrasonic pressure waves from selected acoustoelectric fransducers.

Calibration of the sensor arrays of underwater or underground imaging systems is

effectuated in a manner known in the art by disposing a reference object of known shape and

dimensions at a predetermined location and in a specified orientation with respect to the

fransducer assembly. The imaging system is then operated and adjustments made in

processing parameters until the shape, position and orientation of the reference object as

calculated in response to the reflected waves matches the known shape, position and

orientation.

Where a transducer assembly comprises a plurality of rigid frames or carriers each

holding a plurality of transducers, the relative locations and orientations of the different

frames or carriers may be determined by an ancillary detection system utilizing energy

different from acoustic or ulfrasonic pressure waves. Where at least a portion of each frame or

carrier is disposed in a light-transmitting medium, whether the atmosphere or an upper layer of a body of water, optical radiation may be used to monitor the positions and orientations of

the frames or carriers relative to each other. Each pair of adjacent transducer-carrying frames

is provided with a plurality of interferometers or metrology devices which automatically count

interference fringes to determine the instantaneous distance between two points each located

on a respective one of the adjacent frames. More specifically, one frame is provided at a first

point with a laser emitting diode disposed on a substrate with an interference grating and a

solid-state optical sensor, while the adjacent frame is provided at a second, counterpart, point

with an anisotropically etched silicon minor. The optical sensor or receiver is connected to a

finge counter which determines the distance between the first point on the one frame and the

second point on the adjacent frame. Several such mefrology systems provided on the two

adjacent transducer-carrying frames enable an automatic determination of the six degrees of

freedom (three translational coordinates and three rotational coordinates) of the one frame

relative to the other.

Of course, a separate distance measuring system which uses acoustic or ulfrasonic

pressure waves may measure the relative positions and orientations of multiple transducer-

carrying frames. Several such acoustic-type interferometric or mefrology systems may be

provided for each pair of adjacent frames.

Pattern matching may be used to effectively determine relative positions and

orientations of a multiplicity of sensors in an anay in cases where the sensors are disposed in

contact with a curvilinear surface, rather than held in fixed relative positions by a rigid

common carrier or frame. In this case, sensors are disposed in sub-arrays on independently movable rigid plates or tiles. Through digital signal processing techniques, the total sensor

anay may be alternatively operated in two modes. In a first mode, pressure wave generators or sensors mounted on a single plate are electronically configured to image structures in a

nanow volume normal to each respective plate, the geometry of transducers on a plate being

fixed. Common features in overlapping images formed by this method are matched to

determine displacement and rotation of neighboring plates (calibration). In a second operating

mode, the full anay of sensors is utilized cooperatively to construct a single global image of

greater geometric fidelity and resolution. These modes may be executed once sequentially or

else iteratively and alternatively, refining and tracking an operating solution. An "operating

solution" means a simultaneous determination of acoustically detected spatial structures, in

particular of surfaces where partial reflection is occurring, and of the positions and

orientations of sensors with respect to each other and detected structures. "Tracking" a

solution means continually updating a best estimate thereof. A first mode of operation may

only be required for bootstrapping, i.e., where an approximate prior solution is unavailable.

Further, for the purposes of this disclosure, "opaque" or "optically impenetrable" shall

mean "scattering or absorbing light to a degree which renders practical optical image

formation impossible over a range of interest", whether of not completely optically opaque.

Although the invention has been described in terms of particular embodiments and

applications, one of ordinary skill in the art, in light of this teaching, can generate additional

embodiments and modifications without departing from the spirit of or exceeding the scope of

the claimed invention. Thus, the drawings and descriptions herein are examples to facilitate

comprehension of the invention and should not be construed to limit the scope thereof.

Claims

CLAIMS:

1. A method for use in detecting hidden objects, comprising:

providing a plurality of electromechanical fransducers including at least one

electroacoustic pressure wave generator and at least one acoustoelectric sensor;

determining locations of said fransducers relative to one another;

energizing said pressure wave generator to produce an outgoing pressure wave;

fransmitting said outgoing pressure wave through an effectively opaque or optically

impenetrable medium;

sensing incoming pressure waves reflected by hidden surfaces generally in or below

said medium in response to said outgoing pressure wave; and

analyzing said incoming pressure waves to determine three-dimensional shapes of said

hidden surfaces.

2. The method defined in claim 1 wherein the providing of said plurality of

elecfromechanical transducers includes disposing said transducers above a selected surface in

pressure- wave transmitting contact with said medium, the transmitting of said outgoing

pressure wave through said medium includes transmitting said outgoing pressure wave

through said selected surface, the analyzing of said incoming pressure waves includes

determining three-dimensional shapes of hidden objects disposed below said selected surface.

3. The method defined in claim 2 wherein said electromechanical fransducers are all

attached to a common carrier, the disposing of said electromechanical transducers above said

selected surface includes moving said carrier into position above said selected surface.

4. The method defined in claim 3 wherein said carrier is flexible, the disposing of said

elecfromechanical fransducers above said selected surface including placing said carrier in

contact with said selected surface.

5. The method defined in claim 4 wherein the locations of said transducers are

determined after the placing of said carrier in contact with said selected surface, determining

the locations of said fransducers relative to one another includes analyzing pressure waves

transmitted directly from said pressure wave generator to said sensor.

6. The method defined in claim 3 wherein said carrier is substantially rigid, the

disposing of said elecfromechanical fransducers above said selected surface including holding

said carrier above and spaced from said selected surface.

7. The method defined in claim 6 wherein said selected surface is a ground surface and

said carrier is mounted to a land vehicle, the disposing of said elecfromechanical transducers

above said selected surface including moving said land vehicle over a ground surface.

8. The method defined in claim 6 wherein said carrier is mounted to an air-borne

vehicle, the disposing of said electromechanical fransducers above said selected surface

including moving said air-borne vehicle over a ground surface.

9. The method defined in claim 3 wherein said carrier and said elecfromechanical

transducers are air-borne, the disposing of said elecfromechanical transducers above said selected surface including suspending said carrier and said electromechanical fransducers over

said selected surface.

10. The method defined in claim 2 wherein said selected surface is a ground surface

and wherein said outgoing pressure wave and said incoming pressure waves are ultrasonic,

further comprising wetting a ground structure contiguous with said selected surface to

facilitate transmission of said outgoing pressure wave and said incoming pressure waves

! through said ground structure.

11. The method defined in claim 2 wherein said hidden objects include land mines,

further comprising detonating said land mines after identification of said hidden objects as

land mines.

12. The method defined in claim 2 wherein the analyzing of said incoming pressure

waves includes determining shapes of said hidden objects and comparing said shapes with a

reference library of possible objects.

13. The method defined in claim 1 wherein said outgoing pressure wave has a plurality

of different frequencies.

14. The method defined in claim 13, further comprising generating said different frequencies at different times.

15. The method defined in claim 1, further comprising generating a video signal

encoding an image of one of said hidden surfaces and transmitting said video signal to a video

monitor, also comprising selecting said image from among a multiplicity of possible images

of said hidden surfaces, additionally comprising subsequently selecting a different image from

among said possible images and displaying said different image on said monitor.

16. The method defined in claim 1 wherein the providing of said elecfromechanical

fransducers includes operating a remote confrol robot to shift said transducers into a

predetermined position in pressure-wave transmitting communication with said medium.

17. A system for detecting objects hidden underground, comprising:

a carrier movable over a land surface;

a plurality of electromechanical transducers mounted to said carrier, said

elecfromechanical fransducers including at least one elecfroacoustic pressure wave generator

and at least one acoustoelectric sensor;

means operatively connected to said electromechanical transducers for determimng

locations of said fransducers relative to one another;

a source of alternating electrical cunent operatively connected to said pressure wave

generator for energizing said generator to produce an outgoing pressure wave fransmittable to

an effective extent through upper layers of a ground formation;

a wave analyzer operatively connected to said sensor for analyzing incoming pressure

waves reflected by an underground surfaces in response to said outgoing pressure wave, to

determine three-dimensional shapes of underground objects; and

.a propulsion mechanism operatively connected to said carrier for moving said carrier

over said land surface.

18. The system defined in claim 17 wherein said carrier is a flexible web.

19. The system defined in claim 18 wherein said web is a part of a container holding a

fluid medium.

20. The system defined in claim 19 wherein said container includes a substantially

rigid panel and flexible panels connected to said rigid panel.

21. The system defined in claim 17, further comprising a video signal generator

operatively connected to said wave analyzer for producing a video signal encoding an image

of an underground object, said video signal generator being operatively connected to a video

monitor for displaying said image.

22. The system defined in claim 17 wherein carrier is mounted to a land vehicle

incorporating said propulsion mechanism.

23. The system defined in claim 17 wherein carrier is mounted to an air-borne vehicle

incorporating said propulsion mechanism.

24. The system defined in claim 17 wherein said carrier and said elecfromechanical transducers are air-borne, the disposing of said elecfromechanical transducers above said

ground structure including suspending said carrier and said electromechanical fransducers

over said ground surface.

25. The system defined in claim 17 wherein said source includes means for producing

a plurality of different frequencies.

26. The system defined in claim 17, further comprising means operatively connected

to said propulsion mechanism for remotely controlling said propulsion mechanism.

27. A system for underground surveying, comprising:

a plurality of substantially rigid frames;

a plurality of acoustoelectric sensors for generating electrical signals encoding echo

responses of underground surfaces, each of said frames carrying at least one of said sensors,

said sensors being disposable in effective physical contact with underground structures upon

an insertion of said frames through a ground surface;

an acoustic energy generator disposable in effective physical contact with said

underground structures;

position determination componentry operatively connected to said sensors for

determining locations of said sensors relative to one another;

an electronic signal processor operatively connected to said sensors for analyzing said

electrical signals in accordance with the determined locations of said sensors to determine

surfaces of an object hidden underground and for generating a video signal encoding an image of said object; and

a video monitor operatively connected to said processor for displaying the image of

said object.

28. The system set forth in claim 27 wherein said acoustic energy generator is an

elecfroacoustic fransducer, further comprising an a-c cunent generator operatively connected

to said electroacoustic fransducer for energizing said elecfroacoustic fransducer with an

electrical signal of a pre-established ulfrasonic frequency.

29. The system defined in claim 28 wherein said elecfroacoustic transducer is one of a

plurality of elecfroacoustic transducers mounted to said frames, further comprising means

operatively connected to said electroacoustic fransducers for energizing said elecfroacoustic

fransducers in a predetermined sequence.

30. The system set forth in claim 27 wherein said processor includes an analyzer

operatively connected to said sensors for determining a three-dimensional shape of said object

by analyzing signals generated by said sensors in response to pressure waves produced at said

object in response to pressure waves produced by said acoustic energy generator.

31. The system defined in claim 27 wherein said processor includes a view selector

operatively connected to said video monitor for selecting said image from among a

multiplicity of possible images of said object.

32. The system defined in claim 27, further comprising a filter stage operatively

connected to said processor and said video monitor for eliminating a selected surface from

said image.

33. The system defined in claim 27 wherein said sensors include a plurality of

acoustoelectric fransducers mounted to said frames, further comprising means operatively

connected to said fransducers for receiving signals from said acoustoelectric fransducers in a

predetermined sequence.

34. The system set forth in claim 27 wherein said position determination component

includes an additional processor for analyzing additional electrical signals generated by said

sensors in response to pressure waves transmitted underground directly from said acoustic

energy generator to said sensors.

35. A method for underground surveying, comprising:

disposing an anay of acoustoelectric sensors in operative contact with a ground

formation capable of transmitting pressure waves;

after the disposing of said anay of acoustoelectric sensors in operative contact with

said ground formation, determining physical locations of said acoustoelectric sensors relative

to each other;

said ground formation, generating a pressure wave in said ground formation;

after the generating of said pressure wave, energizing said acoustoelectric sensors to generate a series of electrical signals encoding echo responses of underground surfaces to

said pressure wave;

automatically analyzing said electrical signals to generate a video signal encoding an

image of said surfaces; and

feeding said video signal to a video monitor to thereby display said surfaces on said

monitor.

36. The method defined in claim 35 wherein said acoustoelectric sensors are mounted

to a plurality of substantially rigid frame members, the disposing of said anay of said

acoustoelectric sensors including inserting said frames through a ground surface and into said

formation.

37. The method defined in claim 36 wherein said frame members each have an

elongate dimension, the disposing of said anay of acoustoelectric sensors including disposing

said frame members so that the respective elongate dimensions extend approximately parallel

to a gravity vector.

38. The method defined in claim 36 wherein said frame members each have an

said frame members so that the respective elongate dimensions extend at an acute angle

relative to a gravity vector.

39. The method defined in claim 35 wherein said acoustoelectric sensors are mounted to a fluid filled container, the disposing of said array of said acoustoelectric sensors including

disposing said container on said formation.

40. The method defined in claim 39 wherein said container has a wedge shape with a

first wall and a second wall disposed at an angle relative to one another, said acoustoelectric

sensors being fixed to said second wall, the disposing of said anay of acoustoelectric sensors

including disposing said first wall in contact with said formation and said second wall at said

angle with respect to said first wall.

41. The method defined in claim 40 wherein the disposing of said container on said

formation includes disposing said container in an arcuate configuration along an upper surface

of said formation.

42. The method defined in claim 35, further comprising introducing a liquid into said

formation.

43. The method defined in claim 35 wherein the disposing of said acoustoelectric

sensors in operative contact with said formation includes deploying a carrier on said formation, said acoustoelectric sensors all being attached to said carrier.

44. The method defined in claim 35 wherein the energizing of said acoustoelectric

sensors including receiving signals from said acoustoelectric sensors in a predetermined

sequence.

45. The method set forth in claim 44 wherein determining the physical locations of

said acoustoelectric sensors includes analyzing additional electrical signals generated by said

acoustoelectric sensors in response to pressure waves transmitted through said formation

directly from a pressure wave generator to said acoustoelectric sensors .

46. The method set forth in claim 35 wherein the analyzing of said electrical signals

includes analyzing said electrical signals to determine a three-dimensional shape of an object

defined by at least one of said surfaces.

47. The method defined in claim 46, further comprising selecting said image from

among a multiplicity of possible images of said surfaces, further comprising subsequently

selecting a different image from among said possible images and displaying said different

image on said monitor.

48. The method defined in claim 46, further comprising eliminating at least a portion

of a selected object from said image to thereby show on said monitor an image of an object

behind the eliminated portion of said selected object.

49. The method defined in claim 35 wherein the generating of said pressure wave is

accomplished by energizing an electroacoustic transducer which is one of a plurality of

elecfroacoustic transducers disposed in a predetermined configuration, further comprising

energizing said fransducers in a predetermined sequence.

50. A system for surveying an underwater topography, comprising:

ultrasonic sensor means disposable in physical contact with a body of water for

generating electrical signals encoding ulfrasonic echo responses of underwater objects in said

body of water, said sensor means including a plurality of elecfromechanical transducers in

turn including at least one elecfroacoustic transducer and one acoustoelectric transducer, said

electromechanical fransducers being disposed in an array which has at least two dimensions;

an a-c cunent generator operatively connected to said electroacoustic transducer for

energizing said electroacoustic transducer with an electrical signal of a pre-established

ulfrasonic frequency;

position determination means operatively connected to said sensor means for

determining locations of said elecfromechanical transducers relative to one another;

processing means operatively connected to said sensor means for analyzing said

electrical signals in accordance with the determined locations of said elecfromechanical

transducers to determine surfaces of objects disposed at least partially in said body of water

and for generating a video signal encoding an image of said objects; and

a video monitor operatively connected to said processing means for displaying the

image of said objects.

51. The system set forth in claim 50 wherein said sensor means includes a carrier, said

electromechanical transducers being mounted to said carrier.

52. The system set forth in claim 51 wherein said carrier is a net.

53. The system set forth in claim 51 wherein said carrier is a rigid framework.

54. The system set forth in claim 51, further comprising motive means attached to said

carrier for applying a force to said carrier relative to said body of water.

55. The system set forth in claim 50 wherein said processing means includes analyzing

means operatively connected to said acoustoelectric fransducer for determining three-

dimensional shapes of said objects by analyzing signals generated by said acoustoelectric

transducer in response to ultrasonic pressure waves produced at said objects in response to

ulfrasonic pressure waves produced by said electromechanical transducers.

56. The system defined in claim 50 wherein said processing means includes a view

selector operatively connected to said video monitor for selecting said image from among a

multiplicity of possible images of said objects.

57. The system defined in claim 50 wherein said processing means includes a filter

stage operatively connected to said video momtor for eliminating a selected object from said

image.

58. The system defined in claim 50 wherein said electromechanical transducers

include a plurality of electroacoustic fransducers disposed in a predetermined anay, further

comprising means for energizing said elecfroacoustic transducers in a predetermined

sequence.

59. The system defined in claim 50 wherein said elecfromechanical fransducers

include a plurality of acoustoelectric transducers disposed in a predetermined anay, further

comprising means for receiving signals from said acoustoelectric fransducers in a

predetermined sequence.

60. The system set forth in claim 50 wherein said position determination means

includes a substantially rigid carrier, said elecfromechanical fransducers being mounted to

said carrier so that the locations of said electromechanical transducers relative to one another

are fixed by said carrier.

61. The system set forth in claim 50 wherein said position determination means

includes additional processing means for analyzing additional electrical signals generated by

said sensor means in response to pressure waves transmitted through said body of water

directly from said elecfroacoustic fransducer to said acoustoelectric fransducer.

62. The system set forth in claim 50 wherein said elecfromechanical transducers

include a single electroacoustic fransducer and a plurality of acoustoelectric fransducers, said

sensor means including means for sampling output signals of said acoustoelectric transducers

in a predetermined sequence.

63. The system set forth in claim 50 wherein said electromechanical transducers

include a plurality of elecfroacoustic fransducers and a single acoustoelectric fransducer, said

sensor means including means for activating said electroacoustic fransducers in a predetermined sequence.

64. A method for surveying an underwater topography, comprising:

disposing an anay of elecfroacoustic transducers in operative contact with a body of

water;

determining physical locations of said fransducers relative to each other;

energizing said transducers to generate a series of electrical signals encoding echo

responses of underwater objects in said body of water, said echo responses conesponding to a

multiplicity of pressure wave paths from said fransducers to each of said objects and back to

said transducers;

image of said objects; and

feeding said video signal to a video monitor to thereby display said objects on said

monitor.

65. The method defined in claim 64 wherein the disposing of said fransducers in

operative contact with said body of water includes deploying a carrier in said body of water,

said transducers all being attached to said carrier.

66. The method set forth in claim 65, further comprising operating propulsion devices

attached to said carrier, thereby moving said carrier relative to said body of water.

67. The method set forth in claim 66 wherein said carrier is a net, further comprising operating said propulsion devices to pull in opposing directions on said net to maintain said

net in an extended configuration.

68. The method set forth in claim 66 wherein the operating of said propulsion devices

includes differentially operating said propulsion devices to change an orientation of said

carrier relative to said body of water and relative to said objects.

69. The method defined in claim 64 wherein said elecfromechamcal transducers

include a plurality of acoustoelectric sensors, the energizing of said fransducers including

receiving signals from said sensors in a predetermined sequence.

70. The method set forth in claim 69 wherein determining the physical locations of

said transducers includes analyzing additional electrical signals generated by said sensors in

response to pressure waves fransmitted through said body of water directly from selected ones

of said transducers to said sensors.

71. The method set forth in claim 64 wherein the analyzing of said electrical signals

includes analyzing said electrical signals to determine three-dimensional shapes of said

objects.

72. The method defined in claim 64, further comprising selecting said image from

among a multiplicity of possible images of said objects, further comprising subsequently

selecting a different image from among said possible images and displaying said different image on said monitor.

73. The method defined in claim 64, further comprising eliminating at least a portion

behind the eliminated portion of said selected object.

74. The method defined in claim 64 wherein said fransducers include a plurality of

pressure wave generators disposed in a predetermined configuration, the energizing of said

transducers includes energizing a plurality of said pressure wave generators in a

predetermined sequence.

75. The method set forth in claim 64 wherein said fransducers include a single pressure

wave fransducer and a plurality of pressure wave sensors, the energizing of said fransducers

including sampling output signals of said sensors in a predetermined sequence.

76. A system for surveying an underwater topography, comprising:

ulfrasonic sensor means disposable in physical contact with a body of water for

body of water, said sensor means including a plurality of elecfromechanical fransducers in

turn including at least one electroacoustic transducer and one acoustoelectric fransducer, said

an a-c current generator operatively connected to said elecfroacoustic transducer for energizing said electroacoustic transducer with an electrical signal of a pre-established ultrasonic frequency;

position determination means operatively connected to said sensor means for

determining locations of said elecfromechanical transducers relative to one another; and

processing means operatively connected to said sensor means for analyzing said

electrical signals in accordance with the determined locations of said electromechanical

transducers to determine surfaces of objects disposed at least partially in said body of water,

said processing means including pattern recognition circuitry for comparing the determined

object surfaces with a stored electronic library of stored surface data to identify the

determined object surfaces as being consistent with a predetermined class of objects.

77. The system defined in claim 76, further comprising:

additional position determination means operatively connected to said processing

means for determimng locations of said determined object surfaces relative to a global frame

of reference; and a recording component operatively connected to said processing means and said

additional position determination means for recording locations of said determined object

surfaces relative to said global frame of reference.

78. The system defined in claim 77 wherein said recording component includes an

electronic data store.

79. The system defined in claim 77 wherein said recording component includes a

printer.

80. The system defined in claim 76 wherein said underwater sensor means includes a

carrier, said fransducers being mounted to said carrier, further comprising motor means

operatively connected to said carrier for moving said carrier through said body of water.

81. The system defined in claim 80 wherein said pattern recognition circuitry is

operatively connected to said motor means for anesting said motor means upon detecting that

one of said determined object surfaces falls into a predetermined class of objects of interest.

82. The system defined in claim 80 wherein said motor means is mounted to said

carrier so that said carrier is self-propelled.

83. The system defined in claim 80 wherein said motor means is mounted to a vessel,

said vessel being tied to said carrier.

84. The system defined in claim 76 wherein said processing means is operatively

connected to said sensor means via a wireless communications link.

85. The system defined in claim 76 wherein said processing means includes a video

signal circuit generating a video signal encoding an image of said determined object surfaces,

further comprising a video momtor operatively connected to said processing means for

displaying the image of said determined object surfaces.

86. The system defined in claim 85 wherein said processing means includes a view selector operatively connected to said video monitor for selecting said image from among a

multiplicity of possible images of said objects.

87. The system defined in claim 85 wherein said processing means includes a filter

stage operatively connected to said video monitor for eliminating a selected object from said

image.

88. The system set forth in claim 76 wherein said processing means includes analyzing

means operatively connected to said acoustoelectric transducer for determining three-

transducer in response to ulfrasonic pressure waves produced at said objects in response to

ulfrasonic pressure waves produced by said elecfromechanical transducers.

89. The system defined in claim 76 wherein said elecfromechanical fransducers

include a plurality of elecfroacoustic transducers disposed in a predetermined array, further

comprising means for energizing said elecfroacoustic fransducers in a predetermined

sequence.

90. The system defined in claim 76 wherein said electromechanical transducers

include a plurality of acoustoelectric fransducers disposed in a predetermined array, further

predetermined sequence.

91. The system set forth in claim 76 wherein said position determination means

includes a substantially rigid carrier, said electromechanical transducers being mounted to

said carrier so that the locations of said elecfromechanical fransducers relative to one another

are fixed by said carrier.

92. A method for surveying an underwater topography, comprising:

disposing an anay of elecfroacoustic fransducers in operative contact with a body of

water;

determining physical locations of said transducers relative to each other;

energizing said fransducers to generate a series of electrical signals encoding echo

multiplicity of pressure wave paths from said transducers to each of said objects and back to

said fransducers;

automatically analyzing said electrical signals to determine surfaces of objects

disposed at least partially in said body of water, said analyzing including comparing the

93. The method defined in claim 92, further comprising:

determining locations of said determined object surfaces relative to a global frame of

reference; and

automatically recording locations of said determined object surfaces relative to said

global frame of reference.

94. The method defined in claim 92 wherein said fransducers are mounted to a carrier,

further comprising operating a motor to move said carrier through said body of water.

95. The method defined in claim 94, further comprising automatically stopping said

motor upon detecting that one of said determined object surfaces falls into a predetermined

class of objects of interest.

96. The method defined in claim 92, further comprising generating a video signal

encoding an image of said determined object surfaces, and displaying the image of said

determined object surfaces.

97. The method defined in claim 96, further comprising automatically eliminating a

selected object from said image.

98. The method defined in claim 92 wherein said elecfromechanical fransducers

receiving signals from said sensors in a predetermined sequence.

99. The method defined in claim 92, further comprising selecting said image from

image on said monitor.

100. A system for surveying an underwater topography, comprising:

a substantially rigid carrier body;

propeller means on said carrier body for propelling said carrier body through a body of

water;

ultrasonic sensor means, attached to said carrier body so as to be disposable together

with said carrier body in operative contact with a body of water, for generating electrical

signals encoding ulfrasonic echo responses of underwater objects in said body of water, said

sensor means including a plurality of elecfromechanical transducers in turn including at least

one elecfroacoustic fransducer and one acoustoelectric transducer, said elecfromechanical

transducers being disposed in an array on said carrier body which has at least two dimensions;

an a-c cunent generator operatively connected to said elecfroacoustic transducer for

energizing said elecfroacoustic fransducer with an electrical signal of a pre-established

ulfrasonic frequency;

processing means operatively connected to said sensor means for analyzing said

fransducers to determine surfaces of objects disposed at least partially in said body of water

and for generating a video signal encoding an image of said objects; and

image of said objects.

101. The system defined in claim 100 wherein said carrier body is a manned

submarine.