RU2438149C2 - Independent bottom station for seismic observations - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: station consists of stationary and external housings. Unit of seismic receivers, analogue amplifiers, low-pass filters, remote digital recorder and correct time unit are arranged in stationary tight housing. Stationary housing is equipped with ballast and installed on the frame. External housing is made in the form of sphere inside which there arranged is central computer, hard disk unit, hydrophone, unit of hydroacoustic communication channel, hydrophysical module, ballast opening connection, timer of opening connection, flashing beacon, radio beacon, external communication connector and power source. External housing is connected to stationary housing by means of cable rope. Stationary and external housings are located from each other at distance of 50-100 m.

EFFECT: improving prediction accuracy of abnormal phenomena; enlarging functional capabilities.

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Description

The invention relates to the field of geophysics, and more particularly to devices for measuring geophysical parameters in the bottom zone of the seas and oceans, and can be used to quickly assess the seismic and hydrodynamic conditions of regions and to predict possible seismic and environmental consequences of a natural and man-made nature.

Known autonomous bottom stations [1-3] are cylindrical or spherical bodies, equipped with ballast for mounting them on the ground, inside and on the body of which measuring sensors and means of processing primary information are installed. As measuring sensors are used, as a rule, hydrophones and geophones. The information registered by the sensors is stored on flash cards, which, after lifting the bottom stations, are processed at control centers or read through sonar channels. Known bottom stations are intended mainly for recording seismic signals in the sea. So, the device [3] is a sea autonomous bottom seismic station installed on the seabed mainly from floating means. The station includes a sealed enclosure, consisting of two hemispheres, equipped with a sealing ring at the joint. Geophysical equipment is located inside, including measuring sensors for geophonic and hydrophone types, modules for receiving, registering, converting and storing registered signals, interface units with the airborne module during ascent, satellite and sonar communication channels, orientation unit, synchronization unit, disconnector control unit and power supply unit . Hydroacoustic and satellite antennas, means for searching the bottom station during ascent, rigging elements and connectors, a device for placing on the bottom and for ascent of the bottom station, made in the form of a ballast, are installed on the outer surface of the hull.

However, the known autonomous bottom stations for measuring seismological and hydroacoustic signals on the seabed operate in a continuous recording mode and, due to insufficient memory and insufficient charge of the power source, have a limited life.

Autonomous bottom stations [4-8] are also known, including a bottom seismometer, a hydrophysical module, a magnetic field sensor, an optical measurement unit, primary information processing and storage facilities, communication tools with a control station installed on the platform, in which, to increase the operating time by registration is performed in the start-stop (standby) mode of accumulation of information. The drive is controlled from a special device in which the average level of the seismic background is continuously determined for a large period of time and at the same time for a small period commensurate with the average duration of earthquake signals. The ratio of these levels is used as a threshold value for turning on the drive. Since such a control device has inertia, a limited amount of buffer memory is used to eliminate the loss of the initial part of the signal. If the threshold value is exceeded, the signal is overwritten from the buffer to the drive.

However, such a system only responds to earthquakes of a certain duration and intensity. At the same time, the duration of earthquake signals can range from units of seconds (local weak) to units of hours (strong remote), and their intensity can vary by several orders of magnitude. On the other hand, such a system is highly susceptible to interference that leads to false recordings. For example, periodic signals from the airgun used in seismic exploration, or signals from underwater sonar communication, as well as pulsed biological noise, can completely fill the drive and lead to premature discharge of the power source.

Another disadvantage of the known technical solutions is that the composition of the measuring means included in them does not allow solving the problem associated with the study of the state of the marine environment in the near-bottom zone when interacting with tectonic processes, as well as the task of geophysical monitoring of complex hydraulic structures. This is due to a number of problems associated with the influence of bottom currents on instrumental noise, soft-seismic coupling of seismic receivers, microseismic noise generated by gravitational waves, and the propagation of seismic signals in the oceanic crust.

In addition, such a significant drawback of the known devices as insufficient memory of the information storage device (registered signals) does not allow to fully implement the determination of the correlation and spectral functions of random processes in the continuous recording of microseisms.

The objective of the proposed technical solution is to increase the reliability of the forecast of anomalous phenomena by expanding the functionality of autonomous bottom stations.

The problem is solved due to the fact that in the device, which is an autonomous bottom station for seismic observations, connected by a hydroacoustic communication channel to a control station and consisting of a sealed enclosure permanently mounted on the frame, and containing means for recording geophysical signals, including a bottom seismometer, hydrophysical module, information storage facilities, communication facilities with a control station, spatial orientation sensor, beacon, ballast, ballast breaker and further introduced analog amplifiers and filters low frequencies, a digital recorder and the remote unit precise time; in addition, the hydrophysical module is installed in a remote housing made in the form of a sphere, which also houses a central computer, a hard disk drive, a hydrophone, a unit for a hydroacoustic communication channel, a ballast switch, a breaker timer, a flashing beacon, a beacon, an external communication connector, a source nutrition; the remote housing is secured to the frame by means of a cable cable connected to the housing mounted on the frame; stationary and remote buildings are separated from each other at a distance of 50-100 m

New distinguishing features are that analog amplifiers and low-pass filters, a remote digital recorder and an accurate time unit are additionally introduced into the device; the hydrophysical module is installed in a remote housing made in the form of a sphere, which also houses a central computer, a hard disk drive, a hydrophone, a unit for a hydroacoustic communication channel, a ballast breaker, a breaker timer, a flashing beacon, a beacon, an external communication connector, a power source; the remote housing is secured to the frame by means of a cable cable connected to the housing mounted on the frame; stationary and remote buildings are separated from each other at a distance of 50-100 m

The set of distinctive features allows us to solve the technical problem of not only the operational assessment of the seismic state of the studied areas, but also the task of the operational assessment of the hydrodynamic state at the water-soil boundary, due to the influence of the environment under the influence of natural and technogenic processes. Thus, the set of distinctive features of the claims provides the achievement of a technical result, which consists in expanding the functionality of known devices.

To reduce interference from bottom currents, the station is made of two strong spherical bodies spaced in space. One hull (with a diameter of 450 mm) with a block of seismic sensors lies at the bottom, the second hull (with a diameter of 650 mm) with recording equipment, a power source, a sonar channel and auxiliary devices is in a floating state above the bottom. The enclosures are connected electrically and mechanically by a robust cable cable from 50 to 100 m long.

The essence of the technical solution is illustrated by the drawing, which shows a block diagram of an autonomous bottom station for seismological observations. The block diagram includes spherical housings 1 and 2, spaced 50-100 m apart. Housings 1 and 2 are connected by an electrically and mechanically robust cable-cable 3. The central microprocessor 4, the hard disk drive 5, the hydrophone 6 are placed in the housing 1 , unit of the hydro-acoustic communication channel 7, ballast breaker 8, breaker timer 9, flashing beacon 10, external communication connector 11, power supply 12, hydrophysical module 13, radio beacon (not shown). Housing 2 contains a three-component block of seismic receivers 14, analog amplifiers 15, low-pass filters 16, a remote digital recorder 17, an accurate time storage unit 18. Antenna 19 is installed on housing 1. The housing 2 is equipped with a ballast 20 and is stationary mounted on the frame 21.

Frame 21 is a metal structure and is the basis of an underwater observatory.

An autonomous bottom station consists of two spherical bodies 1 and 2 connected by a cable-cable 3. Body 2 has negative buoyancy due to ballast 20. Body 1 has positive buoyancy and is held at the bottom by a cable. The spatial separation (from 50 to 100 m) of buildings 1 and 2 is carried out to eliminate the influence on the quality of registration of seismic signals of bottom currents. The station is put to the bottom in free fall by dropping overboard from the supporting vessel. The rise of the station is as follows. According to the hydroacoustic signal from the vessel, received through the hydroacoustic antenna of the unit of the hydroacoustic communication channel 7, the ballast switch 8 is activated, and the station pops up. A station is searched on the surface using a flashing beacon 10 (at night).

The seismic receiver unit 14 is designed to provide continuous seismic monitoring of the seabed in a wide frequency and dynamic ranges.

It includes seismic sensors, seismic acoustic sensor, spatial orientation unit.

Seismic sensors are three components of seismic sensors: two horizontal and one vertical, and are designed to convert the speed of oscillation of the soil into an electrical signal in the corresponding dynamic and frequency range. Technical characteristics of seismic sensors are given in the table.

Seismic Sensor Specifications Type of seismic receiver SM-5 Channel type Bicycle meter Number of seismic sensors 3 Frequency range of recorded seismic signals, Hz 0.03-40 Full dynamic range, dB no less 120 Type of output signal Analog, paraphase Range of output signal values, V no more ± 10 Noises reduced to the input at a frequency of 1 Hz, by offset, m, not more 10 ^-9 Amplitude of a calibration signal at a load current of 4 mA, V, no more ± 5 Consumption current, mA, no more 13 Permissible angle of inclination while maintaining operability, angle hail. ± 10

A three-component seismic-acoustic sensor is designed to convert the third derivative of soil vibrations into an electrical signal in the corresponding dynamic and frequency ranges. Key sensor specifications:

the number of seismic-acoustic channels 3, the frequency range of 20-1000 Hz, the dynamic range in the 1/3 octave band and the central frequency of 30 Hz is not less than 60 dB, the amplitude of the output signal is not more than ± 10 V, the amplitude of the control signal at a load current of 4 mA is not more than ± 5 V.

The spatial orientation block is designed to determine the exact position in space of all seismic sensors.

As a sensor, the TCM-2 electric compass module of Precision Navigation company is used, which is a three-axis flux-gate magnetometer and an electronic unit made on one board.

The external communication connector 11 provides communication when connecting external devices during the ascent of an underwater observatory.

The hydrophysical module 13 is designed to perform measurements of the following quantities:

- temperature,

- pressure

- electrical conductivity,

- current velocity vector (triaxial acoustic current meter),

- orientation of the observatory platform (roll-trim values).

Dispatch stations are made in the form of coastal structures or floating equipment (floating, stationary and anchored platforms, ships).

Dispatch station facilities include:

- personal computer compatible with IBM PC,

- receiver of satellite navigation system GPS,

- block autonomous sonar disconnector,

- equipment for sonar telecontrol.

The minimum configuration of a personal computer includes:

- processor - Pentium 166 MHz,

- RAM - 32 MB,

- SVGA card with 1 MB memory,

- An additional board with two serial ports with FIFO memory (UART16550-compatible).

They are used to process information received from the underwater observatory.

The software and mathematical support of the dispatch station’s facilities is designed to check all the measuring channels of the underwater station through the RS-485 serial port, to bind the internal clock to a single time system, to bind to geographic coordinates using the sonar channel equipment 7, to obtain information about the results of test checks after installation underwater observatory to the bottom.

The algorithm of the main mode of operation of the dispatch station is to provide communication between the submarine station and the dispatch station through a fiber optic deep-sea cable using the access method with time division of subscribers. Each submarine station has its own address. In this case, the network of control stations operates in simplex mode. At the same time, up to 16 submarine stations operating in stand-alone maintenance-free mode can be connected to one dispatch station.

The number of measuring channels in each underwater station depends on the problem being solved at a particular location of the submarine station. In principle, the maximum number of digital measuring channels can be up to 30, and analog up to 6.

The control station’s control computer and real-time software and software are designed to control the equipment of the underwater observatory, diagnose its malfunctions, receive data from the underwater observatory and place the received data on information storage devices. The functioning of the entire hardware and software complex is determined by the configuration file, which is created by a special program and sets the presence of underwater observatories, the type of geophysical channels used, channel parameters, as well as the presence or absence of time synchronization equipment.

When the registration program starts, the configuration of the entire network of the underwater observatory is read and the Greenwich time is referenced to within a few tens of microseconds and the corrections are calculated to the quartz frequency of the computer to maintain the station's operation. Following synchronization, there is a survey, programming, synchronization and start-up of equipment of individual underwater stations. The state of equipment of each underwater station is requested (its serviceability, availability of channels, serviceability of channels, etc.). In case of problems, an appropriate message is displayed on the screen (it is also recorded in the operation protocol file). The program of work for each measuring channel, the interrogation frequency, and the gain are transmitted to the underwater station.

Before starting, each remote digital recorder 17 is synchronized by the time of the dispatch station computer (hereinafter, synchronization is carried out every 10 s). During synchronization, the signal transit time from the control room computer to the synchronized registration unit is taken into account. After that, the registration unit starts up and starts collecting data from the measuring channels. The registration unit in each underwater station operates independently and compresses and stores all the information in a buffer memory.

The control computer of the dispatch station cyclically requests data from the corresponding registration unit about the signals registered by the sensors and, if available, receives them and writes them to their buffers in the main memory. After accumulating a sufficient amount of data for the channel, they are overwritten into a file corresponding to the type of channel. Usually these files are located on another computer and are accessible on a local network, although for short-term experiments the system can be configured in such a way that a local disk will be used. With short-term communication breaks (up to 10 min), data is not lost due to the presence of each block of registration of a sufficiently large own buffer. In the process of exchanging data, the operator can calibrate any measuring channel that is part of the control station network. In the event of an emergency (communication breakdown with the underwater station, its breakdown, failure of individual channels or restoration of the above), as well as some normal situations (the occurrence of an event or the calibration of the corresponding measuring channel is triggered), a message is displayed on the screen, including the GMT time of the onset of the situation, names underwater stations and the channel, as well as the message itself. Messages are written to a buffer of 100 lines and to the log file. The buffer can be viewed by the operator at any time.

Measuring sensors of an underwater station, after being placed at the bottom, function for their intended purpose. The signals registered by the sensors are recorded on the information storage means (hard disk drive 5), during communication sessions they are transmitted to the dispatch station, where a complete analysis of the assessment of the seismic and hydrodynamic state of the studied areas is performed, based on which a forecast is made about the possible seismic and environmental consequences of natural and man-caused character.

The collection, digitization and accumulation of signals of broadband seismic sensors is carried out by means of a hardware-software complex for an Intel-compatible processor family and is equipped with debugging, testing and visualization tools. Three signal recording modes are provided: continuous, start-stop according to a given program, and start-stop with control by signal level. System parameters are controlled according to the results of express signal processing based on the analysis of the energy level and spectral composition using fast real-time algorithms.

The hardware of the subsystem for collecting and recording data consists of the following basic elements: a remote digital recorder 17, an exact time storage unit 18, a cable cable 3, a central microprocessor of station 4 with a hard disk drive 5. Let us briefly consider these elements.

Remote digital recorder 17 is a micromodule controller based on an Intel-compatible NEC V25 processor with a PCMCIA flash drive and a standard output communication tool based on the RS232 interface. The microcontroller contains a built-in multi-channel ADC with a serial interface, programmable timers, real-time clocks, digital I / O ports, external hardware interrupt channels and a direct memory access channel. Distinctive features of the controller used are miniature dimensions (100 × 70 × 30 mm), low consumption (0.5 W), high reliability and low cost.

The exact time storage unit 18 is constructed using energy-saving technologies, entirely on CMOS elements. It is used as a generator of reference minute (second) marks for synchronizing the clock of the microcontroller of the central microprocessor 4.

The central microprocessor of 4 stations is assembled on the basis of PC-compatible equipment for industrial automation using a processor board such as MicroPC from Octagon Sistems (USA). The applied design meets the stringent requirements of industrial operation, in particular, it is able to withstand large overloads during impacts and has increased MTBF. Having saved the computing power of a modern personal computer, it has small dimensions, weight and power consumption (several units of watts). Moreover, which is especially important for a sealed bottom station, it does not require additional cooling (fan). The presence of a 16-bit IDE interface for a hard disk drive 5 allows the use of modern high-capacity drives and, accordingly, to increase the battery life of the station using the continuous registration mode. The registration system as a whole is fully compatible with PC and runs on ROM-DOS (DOS 6.22).

To expand the dynamic range of the recorded signals, two gain channels, sensitive and coarse, are allocated for each registered component, with a ratio of gain K ₁ / K ₂ = 2 ⁿ , where n is selected from the level of the real seismic background at the station installation site. Thus, it is possible to bring the dynamic range of the station under low noise conditions to 130 dB using an inexpensive and reliable 12-bit ADC. The exact time service is implemented on the basis of periodic synchronization of the internal clock of the PCR microcontroller with standard minute marks from the exact time storage unit 18.

Since the data of the real-time clock registers of the microcontroller can be updated with some delay, to achieve the required accuracy of the time service, the second marks of the exact time storage unit 18 or a mixture of second and minute marks are used, which are entered through one of the digital inputs of the microcontroller to the clock with the analog conversion frequency signal and are recorded in the least significant bit of the word ADC. Thus, the digitized data contains a pilot bit, the front of which is tied to the front of the reference mark with an accuracy not worse than one reference.

Most of the time, the central microprocessor of 4 stations is in the "Sleep" mode and is turned on only for the time of transferring data from the flash card to the hard disk and to perform control functions for servicing the station. Using the "Sleep" mode can dramatically reduce the energy costs of the station as a whole.

The software of the submarine station is entirely written in the high-level C language, which at the same time allows for fine control of the hardware up to bitwise operations in their registers specific to assembler. The use of Borland C language compilers by appropriately adjusting the compiler environment allows generating codes that are largely invariant to the type and class of the IBM-compatible computer used. As a result, the program turns out to be workable for all types of processors, starting with the 8086/8088 family and ending with 80486 and Pentium.

The version of the program is located in the EPROM microcontroller. The launch of the program for execution and, accordingly, the start of work occurs automatically when power is supplied to the microcontroller.

The seismic signals are digitized using the external interrupt mechanism by the signals of the programmable internal timer of the microcontroller. Digitization and data collection are carried out with pre-processing elements to improve the metrological characteristics of the registration channels.

Analog signals are digitized (analog amplifiers 15) at a higher frequency, then digitally filtered and averaged by “triples” and “fives” followed by discharge until the required sampling frequency is obtained. All filtering procedures in the system are performed in real time using Butterworth's fast recursive filters. Two types of filters are used 16. At characteristic points of a program with a high data channelization rate (for example, with input filtering), it is advisable to use recursive filters with integer coefficients. Such filters do not require floating point calculations and are much faster than their counterparts with "exact" coefficients. However, it should be noted that the procedure of rounding the coefficients causes a number of known problems and, in particular, can lead to instability of the filter. In other characteristic nodes of the program, where samples with a sampling frequency of 100 Hz and below are subject to digital filtering, it is possible to use recursive filters with "exact" coefficients, presented in the form of floating point numbers. Such filters are more stable, functionally closer to their analog prototype, but they lose in speed. Recursive filters of this type are used, in particular, in the algorithm of the detector of seismic signals. Typically, in analog and digital devices, Butterworth high-order filters obtained by cascading second-order links give the best result.

In order to increase the autonomy time of the station, in addition to the continuous operation mode, there is also a standby registration mode with a brief record of the history of the event. To organize the standby mode, the system uses the so-called STA / LTA detector, which is most often used for the purpose of detecting seismic signals, using the algorithm for the ratio of signal energies with short-period and long-period averaging. The disadvantage of such a detector, as you know, is to skip the first entry when working on a highly coherent signal. To improve the characteristics of the detector, a three-channel version was developed using the group coincidence attribute “2 of 3”. This means that the data of the three seismic channels are analyzed by three independent detectors, and the detection signal is generated only when the alarms coincide in at least two of the three channels. This method increases the reliability of the system in standby mode. If an event is detected in the system, a signal is generated that allows you to save the previous data file in external memory, otherwise it is erased. Thus, the standby mode of registration is carried out with the recording of the background before the event.

The program of the remote digital recorder 17 contains a telecommunication driver that supports half-duplex communication mode with the central computer of the bottom station. Communication is based on the original high-performance binary communication protocol using separate RS232 interface signals. Communication and data storage are controlled by a central microprocessor of 4 stations. The management program supports the file organization adopted in DOS. Arrays of data are stored on the hard disk in files whose format meets the accepted station requirements, and if necessary, using the simplest software supervisor, the formats can be integrated into any of the seismological data exchange formats existing in the world practice.

Unlike known devices that use a separate analog recorder with a frequency range from 0.1 to 15 Hz, the proposed device uses a recorder with a lower frequency range from 0.003 Hz.

The operation of the entire station is controlled using a central microprocessor 4 of type MicroPC, and the main accumulation of signals is carried out on the hard disk. All this made it possible to expand the frequency range of the digital recorder to 15 Hz from above, the dynamic range to 120 dB (with automatic switching of sensitivity to 2 sub-bands) and completely eliminate analog recording.

When registering seismic signals at the bottom, one of the important areas of use of broadband bottom seismographs is the study of microseismic noise excited by sea and ocean waves. Microseisms appear in a wide range of frequencies and serve as a natural background that determines the sensitivity threshold of seismographs. By means of the proposed device, characteristic microseisms are also recorded with a period of about 6 seconds, and microseisms with periods of 20 and 100 seconds are detected, which allows one to select both volume P and S waves and Love surface waves (oscillations in the frequency range 0.0125-0 , 05 Hz) and Rayleigh.

The implementation of the device is not of technical complexity, since the device is implemented on commercially available sensors and elements of microelectronics, which allows us to conclude that the claimed technical solution meets the patentability condition "industrial applicability".

Information sources

1. RU 2270464, 02.20.2006.

2. RU 2276388, 05/10/2006.

3. RU 2294000, 02.20.2007.

4. EP 0519031, 12/23/1992.

5.NO 911639, 10.26.1992.

6. EP 0516662, December 9, 1992.

7. Smirnov G.V., Eremeev V.I., Ageev M.D. and other Oceanology: means and methods of oceanological research. - M.: Science, 2005.

8. AU 2002100749, 03/13/2003.

9. GB 2183038, 05/28/1987.

10. US 3449950, 06/17/1969.

11.NO 855258, 06/30/1986.

12. US 5128907.07.07.07.1992.

13.NO 923428, 10/06/1992.

14.NO 923269, 08.20.1992.

15. Kovchin I.S. Autonomous oceanographic measuring instruments. - L .: Gidrometeoizdat, 1991.

Claims (1)

An autonomous bottom station for seismic observations, connected by a hydroacoustic communication channel to the dispatch station and consisting of a sealed enclosure permanently mounted on the frame, and containing means for recording geophysical signals, including a bottom seismometer, a hydrophysical module, storage media, communications with the dispatch station, a sensor spatial orientation, beacon, ballast, ballast disconnector, characterized in that analogue amplifiers and lower filters are additionally introduced frequency, remote digital recorder and accurate time unit; the hydrophysical module is installed in a remote housing made in the form of a sphere, which also houses a central microprocessor, a hard disk drive, a hydrophone, a unit for a hydroacoustic communication channel, a ballast breaker, a breaker timer, a beacon, a radio beacon, an external communication connector, a power source; the remote housing is secured to the frame by means of a cable cable connected to the housing mounted on the frame; stationary and remote buildings are separated from each other at a distance of 50-100 m