RU2194292C2 - Geophysical radar - Google Patents

Abstract

FIELD: geophysics. SUBSTANCE: geophysical radar is related to equipment for geophysical prospecting with use of high-frequency electromagnetic waves and can be used in search for mineral resources, for engineering service lines and other latent inhomogeneities in examined layer of ground surface. Geophysical radar includes control and processing unit, interface, transmitter, transmitting antenna, first mixer of stroboscopic converter, first gate former, receiving antenna, receiver, second gate former, second mixer of stroboscopic converter, first delay line, flip-flop, key, sound indicator, liquid-crystal indicator, second delay line, subtractor, integrator, divider, reference voltage former and comparator. EFFECT: enhanced reliability of detection and identification of objects under surface at various depth of bedding thanks to exclusion of variations of electromagnetic field. 1 dwg

Description

 Radar refers to geophysics, in particular, to geoelectrical exploration devices using high-frequency electromagnetic waves, and can be used in mineral exploration, as well as for the search for utilities and other hidden heterogeneities in the investigated subsurface layer of the earth's surface.

 Known devices for geoelectrical exploration (ed. Certificate of the USSR 321783, 344391, 385251, 397877, 455307, 708277, 746370, 817640, 1078385, 1092453, 1100603, 1151900, 1247805, 1300396, 1317378, 1420574, 1469488 15577, 1539838, 15577; RF patents 2044331, 2105330; A. Petrovsky, Radio wave methods in underground geophysics. - M., 1971 and others).

 Of the known devices, the closest to the proposed is the "Geophysical radar" (RF patent 2105330, G 01 V 3/12, 1996), which is selected as a prototype.

 The principle of operation of this geophysical radar is based on the method of ultra-wideband radar sensing, in which the change in the unsteady electromagnetic field formed by electromagnetic waves reflected from a subsurface object after its irradiation with a probing radio signal is estimated, which is used as a sequence of radio pulses with a small number of periods of high-frequency oscillations in each of them ( down to one). In this case, the separation of the transceiver channels over the air is carried out using two antennas (transmitting and receiving), which form a two-antenna unit. The formation of a probe ultra-wideband radio signal is carried out by the generator 3 of the shock excitation and the transmitting antenna 4.

 At the soil - object interface, characterized by a jump in relative permittivity and specific attenuation, a reflected signal is formed that returns to the receiving antenna. The received ultra-wideband signal with the help of a stroboscopic receiver undergoes a time-scale conversion and is digitized, convenient for presentation and processing. This signal contains information about the depth of the object, and about its shape, material, etc. Useful information is extracted using processing in a special calculator and displayed on the screen of a visual indicator in real time.

 An electromagnetic wave reflecting from a subsurface object acts on the receiving antenna 7. This antenna is also affected by interfering direct radiation of the transmitter 3 and the reflected signal from the air-ground interface.

 To exclude direct radiation from the transmitter 3 and reflections from the air - ground surface and from layers with different depths in the known radar, "vertical gating" is used.

 However, reliable detection and identification of subsurface objects at different depths in some cases is difficult due to the high level of electromagnetic field variations (quasistationary and periodic field components, natural and artificial interference).

 The objective of the invention is to increase the reliability of detection and identification of subsurface objects at different depths by eliminating variations in the electromagnetic field.

 The problem is solved in that a geophysical radar containing a series-connected special computer, an interface, a transmitter, which uses a shock excitation generator and a transmit antenna is connected to the second output, the first mixer of the stroboscopic converter, the second input of which is connected to the second output through the first gate former interface, and a trigger, a series-connected receiving antenna, a second mixer of the stroboscopic converter, the second input for which through the second gate driver is connected to the third output of the interface, the first delay line, a trigger, a key, the second input of which is connected to the output of the second mixer, and an amplifier, the second input of which is connected through the digital-analog converter to the fourth output of the interface, to the fifth, sixth and seventh the outputs of which are connected to a special calculator, sound and liquid crystal indicators, respectively, and an analog-to-digital converter is connected to the second input, a second delay line, a subtraction block are introduced , an integrator, a division unit, a unit for generating a reference voltage and a comparison unit, and a second delay line, a subtraction unit, the second input of which is connected to the output of the amplifier, an integrator, a division unit, the second input of which is connected to the output of the subtraction unit, and connected to the output of the amplifier, and a comparison unit, the second input of which is connected to the eighth output of the interface through the unit for generating the reference voltage, and the output is connected to an analog-to-digital converter.

 The structural diagram of a geophysical radar is shown in the drawing.

 The geophysical radar comprises a processing and control unit 1, an interface 2, a transmitter 3, a transmitting antenna 4, a first stroboscopic transducer mixer 5, a first strobe shaper 6, a receiving antenna 7, a receiver 8, a second strobe shaper 9, a second stroboscopic transducer 10, a first line delays 11, trigger 12, key 13, digital-to-analog converter 14, amplifier 15, analog-to-digital converter 16, sound indicator 17, liquid crystal indicator 18, second delay line 19, subtraction unit 20, and cators 21, division unit 22, the unit 23 forming the reference voltage and the comparison unit 24. Moreover, the interface 2, the transmitter 3 and the transmitting antenna 4 are connected in series to the output of the processing and control unit 1. The mixer 5 is connected in series to the reference output of the transmitter 3, the second input of which is connected to the second output of interface 2 through the gate former 6, and trigger 12. To the output the receiving antenna 7 is connected in series with the mixer 10 of the stroboscopic converter, the second input of which is connected via the gate former 9 to the third output of the interface 2, delay line 11, trigger 12, key 13, the second input of which about connected to the output of the mixer 10, the amplifier 15, the second input of which is connected via the digital-to-analog converter 14 to the fourth output of the interface 2, the delay line 19, the subtraction unit 20, the second input of which is connected to the output of the amplifier 15, the integrator 21, the division unit 22, the second input which is connected to the subtraction unit 20, the comparison unit 24, the second input of which is connected through the block 23 for generating the reference voltage to the eighth output of the interface 2, the analog-to-digital converter 16 and interface 2, to the fifth, sixth and seventh outputs of which dklyucheny spetcvychislitelej 1, the liquid crystal 17 and the sound indicators 18, respectively.

 The principle of operation of the geophysical radar is based on the method of ultra-wideband radar sensing, in which the change in the unsteady electromagnetic field generated by the electromagnetic waves reflected from the subsurface object after its irradiation with a probing radio signal is estimated, which uses a sequence of radio pulses with a small number of periods of high-frequency oscillations in each of them (up to to one). The formation of a probe ultra-wideband radio signal is carried out by the generator 3 of the shock excitation and the transmitting antenna 4.

 At the soil - object interface, characterized by a jump in relative permittivity and specific attenuation, a reflected signal is formed that returns to the receiving antenna. The received ultra-wideband signal with the help of a stroboscopic receiver undergoes a time-scale conversion and is digitized, convenient for presentation and processing. This signal contains information about the depth of the object, and about its shape, material, etc. Useful information is extracted using processing in a special calculator and displayed on the screen of a visual indicator in real time.

 Geophysical radar operates as follows.

 The main mode of radar operation is the "Search" mode. This mode is set automatically when the device is turned on and is used when searching and recognizing subsurface objects.

 When applying power to the radar, the processing and control unit 1 initiates the installation of the initial modes of all nodes of the radar. At the command of the processing and control unit 1, the shock excitation generator 3 generates a probe pulsed ultra-wideband signal in the form of a single sinusoid period with an amplitude of 25 V and a duration of 1 ns, emitted by the transmitting antenna 4 in the direction of the Earth's surface.

 Detection of objects in the "Search" mode is carried out by the operator by moving the antenna unit mounted on the rod in front of him right and left, and moving forward in a given direction. In this case, it is necessary to ensure that the antenna unit moves parallel to the surface being examined at a fixed distance (no more than 5 cm from it). The speed of movement of the antenna unit is selected depending on the search conditions and should be in the range of 0.1-1.0 m / s. During the search, it is necessary to alternate the transverse and longitudinal displacements of the antenna unit in such a way that after each swing from right to left or left to right, the antenna unit moves forward up to 20 cm (by the size of its linear size). In this case, it is necessary to ensure that the entire checked area is examined.

 An electromagnetic wave reflected from a subsurface object acts on the receiving antenna 7. This antenna is also affected by interfering direct radiation of the transmitter 3 and the reflected signal from the air-ground interface. Moreover, large amplitudes will have a direct signal and a signal reflected from the air - soil interface.

 Part of the energy of the probing signal from the reference output of the transmitter 3 is supplied to the first mixer 5 of the stroboscopic converter, where a short strobe pulse is also supplied from the gate former 6. The pulse generated in the mixer 5, which represents the instantaneous value of the probing periodic signal, is supplied to the installation input of the trigger 12. The trigger 12 is transferred to the first (zero) state, in which a negative voltage is formed at its output.

 The reflected signal containing information on the interface between the media and the subsurface object is supplied from the output of the receiving antenna 7 to the second mixer 10 of the stroboscopic converter, where a short strobe pulse from the gate former 9 is also fed. The pulse generated in the mixer 10, which is the instantaneous value of the received a periodic signal, through the delay line 11 enters the second input of the trigger 12. The latter is transferred to the second (single) state, in which a positive voltage was. This voltage is supplied to the control input of the key 13 and opens it. In the initial state, the key 13 is always closed. The delay line 11 is necessary for the most complete control of the influence of reflections from the interface between the media on the operation of the amplifier 15 and subsequent stages. The delay line 11 can be made variable, which will eliminate the influence of direct radiation of the transmitting antenna 4 and signals reflected from the air-ground interface and from layers of different depths, that is, "vertical gating" is carried out, which provides sequential viewing of the subsurface space from the air - soil interface to layers of various depths.

 "Horizontal gating" allows against the background of variations in the electromagnetic field, not related to the electromagnetic wave reflected from the subsurface object, to reliably select subsurface objects in the subsurface layers. To exclude the influence of periodic and quasi-stationary variations of the Earth’s electromagnetic field, periodic measurements of the field strength and the normalization of the difference signal of two successive measurements are carried out, i.e. integrate the difference signal, divide the difference signal into the integrated difference signal. The operation of comparing a normalized signal with a given threshold value allows you to make a decision about the presence or absence of a subsurface object.

 For this, the pulse generated in the mixer 10, which is the instantaneous value of the received periodic signal reflected from the subsurface object, or the pulse due to variations in the electromagnetic field, is transmitted through the public key 13 after amplification in the amplifier 15 to the calculation unit 20 directly and through the delay line 19. Moreover, at each observation point, at least two consecutive measurements of these pulses are made. Then, the operation of subtracting two consecutive measurements is performed. For this, the pulse corresponding to the previous measurement is delayed by the delay line 19 until it is compared with the subsequent pulse in the subtraction unit 20. The operations of integrating the difference signal and dividing the difference signal by the integrated difference signal are performed in blocks 21 and 22. In block 24, the normalized signal is compared with the threshold value of the signal set by block 23. If the threshold level is exceeded, the signal is input to the analog-to-digital converter 16, where it is converted into digital form and supplied through interface 2 to the special computer 1. The digital-to-analog Converter 14 is designed to convert information from block 1 about processing and management.

 The frequency of formation of strobe pulses differs from the stable frequency (100 kg) of the generator, as a result of which the next strobe pulse is shifted relative to the periodic received signal, and the instantaneous values thus formed are added up to the scaled realization of the received signal in time. After analog-to-digital conversion, the data through the interface board 2 goes to the special computer 1, and then to the screen of the liquid crystal indicator 18. The frequency of vertical (horizontal) and horizontal (frame) scans can vary within certain limits. On the screen of the indicator 18 in real time there is a flat luminance picture of subsurface targets.

 The maximum amplitude of the received signal is compared with the set threshold value, above which the audible indicator 17 is turned on.

 The appearance of an audio signal, a visual signal on the screen requires the operator to stop and indicates that an object is located in the detection area of the antenna unit, the origin of which should be established, and if necessary, its location and shape should be clarified. To analyze the object, you should scan the object (moving the antenna unit from the detection boundary to the loss boundary) at a speed determined by the light bar on the indicator screen. The "Scan" mode and the formation of a vertical cut of soil with an object ("Slice" mode) is carried out by switching from the "Search" mode by pressing the "Scan" button. 20 seconds after the signal is processed, a radar image of the object appears on the indicator screen, giving an idea of the shape and size of the object. At the request of the operator, the contrast of the image can be changed using the "<", ">" buttons in the direction of increase or decrease.

 To identify the detected object with the available standards, the operator needs to turn to the trained algorithm, and on the indicator screen, when identifying the detected object with the standard in memory, the corresponding name is displayed (for example, "object 2"). In case of discrepancy, the message "object not recognized" is displayed.

 To determine the material of the detected object, the operator, by pressing the "<" button, proceeds to the basic algorithm. By pressing the "Scan" button, the basic algorithm is launched. The screen displays a message about the type of material: "Metal", "Composite" or "Plastic".

 Pressing the Scan button and moving the antenna unit above the object makes it possible to re-examine the object, if necessary, according to the criteria of the basic and trained algorithms.

 The identification of the detected object by the trained algorithm, the recognition of the type of material by the basic algorithm, the analysis by the operator of the image and the "slice" of the object allow the operator to decide on further actions regarding the detected object and continue exploration.

 The interaction of the processing and control unit 1 with the remaining nodes of the radar, as well as the organization of the management of work is carried out through the interface circuit 2.

 Controls, switching and indication are placed on a common control panel. Various options for using the display in the search mode, as well as the operation of the device in auxiliary modes, do not change the essence of the described physical processes, but are determined only by the program of work of the processing and control unit 1.

 Thus, the proposed radar allows, by eliminating the quasistationary component and periodic variations of the Earth’s electromagnetic field, to achieve a higher reliability of detection and identification of subsurface objects at different depths.

Claims (1)

 A geophysical radar comprising a processing and control unit, an interface, a transmitter, which uses a shock excitation generator and a transmitting antenna connected to a second output, a first stroboscopic mixer, the second input of which is connected to the second output of the interface through the first gate driver, and a trigger, a series-connected receiving antenna, a second mixer of the stroboscopic converter, the second input of which through the second The gate driver is connected to the third output of the interface, the first delay line, a trigger, a key, the second input of which is connected to the output of the second mixer, and an amplifier, the second input of which is connected via a digital-to-analog converter to the fourth output of the interface, to the fifth, sixth, and seventh outputs of which the unit is connected processing and control, sound and liquid crystal indicators, respectively, and an analog-to-digital converter is connected to the second input, characterized in that a second delay line is inserted into it, a subtraction, an integrator, a division unit, a unit for generating a reference voltage and a comparison unit, and a second delay line, a subtraction unit, the second input of which is connected to the output of the amplifier, an integrator, a division unit, the second input of which is connected to the output of the subtraction unit, are connected in series to the output of the amplifier, and a comparison unit, the second input of which is connected to the eighth output of the interface through the unit for generating the reference voltage, and the output is connected to an analog-to-digital converter.