RU2435180C1 - Underwater geophysical station - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: station is in form of an airtight housing with a spherical shape of diameter 450 mm mounted on a frame made from aluminium tubes. Inside the airtight housing there are devices, among them an ocean-bottom seismometre, a hydrophysical module, data storage apparatus, a spatial orientation sensor, a gravimetre and a ballast disconnector. The spatial orientation sensor is mounted on a cardan suspension and the bottom-ocean seismometre is mounted on a movable platform. The airtight housing is made from B95 high-strength aluminium alloy. A protective anticorrosion coating is applied on the housing in form of an anode oxidised alloy with a multilayer paint coat. The station is fitted with buoy line, a ballast and a buoy, which enable its positioning and raising to the surface.

EFFECT: broader functionalities.

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Description

The invention relates to the field of geophysics, and more specifically: to devices for measuring geophysical parameters in the near-bottom zone of the seas and oceans, and can be used for the rapid assessment of the seismic and hydrodynamic conditions of regions and the forecast of possible seismic and environmental consequences of a natural and technogenic nature, as well as the search for underwater hydrocarbon deposits.

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 raising 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 placed inside the station building, 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 hydroacoustic communication channels, orientation unit, synchronization unit, disconnector control unit and Power Supply. 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 well-known autonomous bottom stations for measuring seismological and hydroacoustic signals on the seabed operate in a continuous recording mode and have a limited life due to insufficient memory and insufficient charge of the power source.

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. In addition, 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 instruments 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, and the task of geophysical monitoring of complex hydraulic structures and the search for underwater hydrocarbon deposits, due to a number of problems, related to the influence of bottom currents on instrument noise, soft bottom seismic receivers, microseismic noise, mymi gravitational waves, and the characteristics of seismic signals in the earth's crust oceanic.

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.

A significant drawback of the known technical solutions is also the restriction on the depth of use, which is due to the restriction on the weight and size characteristics that prevent the station from surfacing on its own to remove the recorded information and charge the batteries.

The objective of the proposed technical solution is to expand the functionality of underwater stations.

The problem is solved due to the fact that in the device, which is an underwater geophysical station, consisting of a sealed spherical body permanently mounted on the frame, and containing means for recording geophysical signals installed inside the sealed body on the chassis and including a bottom seismometer, hydrophysical module, information storage devices, a spatial orientation sensor mounted on a gimbal, ballast and ballast disconnector, buoy, additionally introduced gravime tr, as well as a buirp connected to ballast, moreover, the sealed housing is made of high-strength aluminum alloy of type B95 with a protective anticorrosive coating in the form of anodized oxidized alloy with a multilayer paint and varnish coating and has a diameter of 450 mm, the frame is made of aluminum pipes, and the bottom seismometer mounted on a movable platform connected to the chassis with a gimbal.

New distinctive features are that the sealed case is made of high-strength aluminum alloy of type B95 with a protective anti-corrosion coating in the form of anodized oxidized alloy with a multilayer paintwork, the sealed case is made with a diameter of 450 mm, the frame is made of aluminum pipes, the bottom seismometer is mounted on a movable platform connected to the chassis with a gimbal, the underwater geophysical station is equipped with a buirp that is connected to the ballast, an additional gravimeter is introduced.

The combination of distinctive features allows you to quickly evaluate not only the seismic state of the studied areas, but also the hydrodynamic state at the water-soil boundary, caused by the influence of the environment under the influence of natural and technogenic processes, as well as solve the problems of searching for underwater hydrocarbon deposits. Thus, the combination of new distinctive features ensures the achievement of a technical result, which consists in expanding the functionality of known devices.

The essence of the proposed technical solution is illustrated by the drawing, which shows a block diagram of an underwater geophysical station, including a sealed enclosure 1 made in the form of a sphere and mounted on a frame 2. In the enclosure 1 on the chassis 3 there are: a central microprocessor 4, a hard disk drive 5, hydroacoustic communication channel 6, bottom seismometer 7, hydrographic module 8, information storage equipment 9, spatial orientation sensor 10, cardan suspension 11, movable platform 12, gravimeter 13, ballast 14, ballast breaker 15 s measure, external communication connector 16, power source 17, buoy 18, buierep 19, analog amplifiers 20, low-pass filters 21, digital recorder 22, accurate time storage unit 23. The sealed enclosure 1 is provided with an upper pole hole 24 for installing a tight connector 16. A hydrophone 25 is also mounted on frame 2.

The sealed housing 1 is made of a spherical shape with a diameter of 450 mm from high-strength aluminum alloy type B95. The use of this alloy makes it possible to fabricate a robust housing of minimal weight for operation at depths of up to 4000 m. To protect the sealed housing 1 from corrosion in sea water, a comprehensive protective coating in the form of anodic oxidation with a multilayer paintwork is applied. In the upper pole hole of the sealed enclosure 1, an external communication connector 16 is installed for reading information without depressurizing the enclosure 1.

To install an underwater geophysical station on the seabed, the sealed housing 1 is equipped with a frame 2 made of aluminum pipes.

Frame 2 is a metal structure and is the basis of an underwater geophysical station.

Due to the fact that the mass of the underwater geophysical station is relatively large and does not allow it to independently ascend to the surface, the buoyrp 19 with ballast 14 and a surface or submerged buoy 18 is used to set and rise to the surface. Ballast 14 prevents the transmission of buoyer 19 vibrations and jerks from the buoy 18 to building 1 of the underwater geophysical station.

The gravimeter 13 is constructed according to an axisymmetric scheme, which eliminates the cross-dropping effect that occurs with bottom currents of the sea. Software for the technical implementation of the proposed method allows the use of both a marine gravimeter type BGM-3, which is a design of a force-balanced accelerometer in which the working mass is maintained in zero position using a feedback mechanism (string gravimeter), and a three-tensor type 3-DFTG gradiometer.

The movable platform 12 is a biaxial gyro platform with correction from accelerometers, which makes it possible to perform measurements at disturbing accelerations up to 150 - 200 Gal, with a dynamic error at small disturbing accelerations less than 1 mGal. In this case, the stabilization error does not exceed 1 minute, the pumping angles are 30-40 degrees, which makes it possible to perform measurements with disturbing accelerations up to 150-200 Gal.

The power source 17 provides power to the underwater geophysical station. Two nickel-cadmium sealed batteries are used as power sources, which allow for a large number of station settings after recharging. The batteries are located on a movable platform 12 in the immediate vicinity of the bottom seismometer 7.

The installation of the underwater geophysical station from the support vessel is carried out using a buirp 19, pre-wound on the drum of a ship’s winch. First, an underwater geophysical station fixed to the buirep 19 descends overboard the vessel, then after 50-100 m, the ballast 14 is attached to the buirep 19 and only after they sink to the bottom, the buoy 18 attached to the upper end of the buirep is discarded. At depths over 500 m more appropriate to use a submerged buoy. In this case, the ballast 14 is fixed to the buoyrep 19 through the sonic breaker 15, and the length of the buoyrep 19 from the ballast 14 to the flooded buoy is 100-200 m less than the depth at the location of the underwater geophysical station.

The underwater geophysical station is lifted aboard the support vessel in the reverse order. First, buoy 18 is selected to board, the buoyrp 19 is fixed to the drum of the ship’s winch and the ballast 14 and the station are lifted.

In the case of using a submerged buoy, the ascent is as follows. A command is sent to the disconnector 15 from the supply vessel via the hydroacoustic communication channel 6, the ballast 14 is separated and the submerged buoy floats to the surface, dragging the underwater geophysical station along with it. Further, boarding the vessel is carried out, as in the case with a surface buoy.

The bottom seismometer 7 converts the seismic vibrations of the bottom surface into electrical signals. In a specific design, a highly sensitive vertical seismic sensor type SM3KV is used. To ensure high measurement accuracy, it is necessary to maintain the verticality of the measuring axis of the sensor in space at possible tilts of the housing 1. For this, the bottom seismometer is mounted on a special weighted movable platform 12 connected to the chassis 3 by a gimbal 11, which allows the bottom seismometer to occupy a vertical position when the body is inclined from 1 up to 30 degrees. In addition, this design provides, when the cardan is rotated, constant contact of the bottom seismometer 7 with the inner surface of the housing 1, which significantly increases the accuracy of measurements.

The bottom seismometer 7 is a three-component seismic-acoustic sensor designed to convert the third derivative of the vibration of the soil into an electrical signal in the corresponding dynamic and frequency ranges. The main technical characteristics of the sensor: 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 the load current 4 mA no more than ± 5 V.

The spatial orientation sensor 10 is designed to determine the exact position in space of the bottom seismometer 7.

As a spatial orientation sensor 10, the TSM-2 module of the Precision Navigation company is used, which is a three-axis flux-gate magnetometer and an electronics unit, made on one board.

Sealed connector 16 provides communication when connecting external shipboard devices when surfacing an underwater geophysical station.

Hydrophysical module 8 is designed to perform measurements of the following quantities:

- temperature

- pressure

- electrical conductivity,

- current velocity vectors (triaxial acoustic current meter),

- salinity

- temperature.

Sensitive sensors for measuring the hydrophysical module are mounted directly on the frame 2.

The assets of the support vessel include:

- personal computer compatible with IBM PC;

- receiver of satellite navigation system GPS;

- block autonomous sonar breaker;

- 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 (UAKT16550-compatible).

They are used to process information received from the underwater geophysical station.

The software and software for the support vessel is designed to check all the measuring channels of the underwater geophysical station through the RS-485 serial port, to bind to the internal clock single time system, to bind to geographic coordinates using hydroacoustic communication channel equipment 6, to obtain information on the results of test checks after installation of an underwater geophysical station at the bottom.

The control ship’s control computer and real-time software and software are designed to control the equipment of the underwater geophysical station, diagnose its malfunctions, receive data received from the underwater geophysical station, and place the received data on information storage devices. The functioning of the entire hardware-software complex is determined by the configuration file, which is created by a special program and sets the presence of underwater geophysical stations, 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 entire network of the subsea geophysical station is read and the Greenwich time is referenced to within a few tens of microseconds and the corrections to the quartz frequency of the computer are calculated to maintain the functioning of the subsea geophysical station. Following synchronization, a survey, programming, synchronization and start-up of equipment of individual underwater geophysical stations occurs when several underwater geophysical stations are used in the research area. The state of equipment of each underwater geophysical 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 geophysical station.

Before starting, each remote digital recorder is synchronized by the time of the dispatch station computer, and later on, synchronization is carried out every 10 seconds. During synchronization, the signal transit time from the computer of the support vessel 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 geophysical station operates independently and compresses all information and adds it to the buffer memory. The control computer of the support vessel 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 data exchange by the operator, calibration of any measuring channel included in the network of the support vessel can be carried out. In case of emergency situations (disconnection from the underwater geophysical 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 start of calibration of the corresponding measuring channel), a message is displayed on the screen, including the GMT time of the onset of the situation, names of underwater geophysical stations and the channel and the message itself. Messages are also written to a buffer of 100 lines and to the log file. The buffer can be viewed by the operator at any time.

After placing the underwater geophysical station at the bottom, the measuring sensors 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 transferred to the support vessel, 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. Registered seismic signals and parameters of the gravitational and magnetic fields are used to identify subsea hydrocarbon deposits in accordance with well-known methods of morphological analysis (see, for example, [18]).

The collection, digitization and accumulation of signals from the bottom seismometer 7 is carried out by means of a hardware-software complex for an Intel-compatible processor family 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 digital recorder 22, an exact time storage unit 23, a cable communication channel, a central microprocessor 4 with a hard disk drive 5.

Digital recorder 22 is a micromodule controller based on an Intel-compatible NEC V25 processor with a PCMCIA flash drive and 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 23 is designed 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 of industrial electronics meets the stringent requirements of industrial operation, in particular the ability 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 underwater geophysical station, additional cooling (fan) is not required. The presence of a 16-bit IDE interface for the hard disk drive 5 allows the use of modern high-capacity drives and, accordingly, increase the battery life of the underwater geophysical 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 are allocated for each registered component: sensitive and coarse, 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 installation site of the underwater geophysical station. 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 23. Since the data of the real-time clock registers of the microcontroller can be updated with a certain delay, the second marks of the exact time storage unit are used to achieve the required accuracy of the time service 23 or a mixture of second and minute marks, which are entered through one of the digital inputs of the microcontroller per cycle with a conversion frequency of analog trunk signal and written in the LSB of the ADC word. 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 subsea geophysical station is entirely written in a high-level C language, which, at the same time, allows for fine control of hardware up to bitwise operations in their registers, typical for assembler. The use of Borland's C language compilers allows the generation of codes that are largely invariant to the type and class of the IBM-compatible computer used by appropriately adjusting the compiler environment. 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 at a higher frequency, then digitally filtered and averaged by triples and fives, followed by discharge to obtain the desired sampling frequency. All filtering procedures in the system are performed in real time using Butterworth's fast recursive filters. Two types of filters are used. It is advisable to use recursive filters with integer coefficients at the characteristic points of a program with a high data canalization rate (for example, with input filtering). 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 underwater geophysical station, in addition to the continuous mode of operation, there is a waiting mode for recording 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 strongly 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 alarm signals 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 digital recorder 22 contains a telecommunication driver that supports half-duplex communication with the central microprocessor 4. 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 4. The control 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 all measuring sensors of the underwater geophysical station is controlled using a central microprocessor 4 of the MicroPC type, 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.

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Claims (1)

An underwater geophysical station, consisting of a sealed spherical body permanently mounted on the frame, and containing means for recording geophysical signals installed inside the sealed body on the chassis and including a bottom seismometer, hydrophysical module, storage media, a spatial orientation sensor mounted on a gimbal, ballast and ballast breaker, buoy, characterized in that the sealed housing is made of high-strength aluminum alloy type B95 with protective ant a corrosion-resistant coating applied to the casing in the form of an anodized oxidized alloy with a multilayer paintwork, the sealed casing is made with a diameter of 450 mm, the frame is made of aluminum pipes, the bottom seismometer is mounted on a movable platform connected to the chassis with a gimbal, the underwater geophysical station is equipped with a buoyer, which is connected with ballast, an additional gravimeter is introduced.