CN110703335B - A towed underwater geological electrical detection system and method - Google Patents

Abstract

The invention discloses a towed underwater geological electric detection system and a towed underwater geological electric detection method, comprising the following steps: the device comprises an underwater cable, a simple underwater electrode, a water pressure measurement sensing unit, a cable floating and sinking unit, an underwater GPS positioning system, an inflator, an electrical data acquisition and storage module and a data processing module; the underwater cable is fixed with a cable floating and sinking unit which is connected with the inflator; the underwater cable is sequentially connected with the electrical data acquisition and storage module and the data processing module; a simple underwater electrode and a water pressure measuring and sensing unit are fixed on the underwater cable wire; the underwater GPS positioning system comprises a transponder, a shipborne transducer and a GPS; the transponder is fixed at the front, middle and tail simple underwater electrodes on the underwater cable; the transponder is in wireless connection with the shipborne transducer; the GPS is fixed on the tugboat. The towed underwater geological electric method detection system and method provided by the invention solve the defects and problems still existing in the conventional underwater geological electric method detection and have good application prospects.

Description

A towed underwater geological electrical detection system and method

Technical Field

The present invention relates to the field of geophysical exploration technology, and more particularly to a towed underwater geological electrical detection system and method.

Background Art

With the acceleration of my country's urbanization process, infrastructure construction in various regions is in full swing. Among them, underwater infrastructure related to underwater rock and soil structures, underwater environmental resources, and underwater engineering construction projects across rivers has increased year by year. Therefore, it is of vital importance to analyze and judge geological information such as underwater geological structures in advance through relevant technical detection means for later engineering design, measures formulation, and safe construction.

At present, the technical means to obtain underwater geological structure and anomalies include drilling, ground penetrating radar, transient electromagnetic, sonar, seismic exploration, conventional electrical exploration, etc. Drilling can directly obtain underwater geological information at a certain location underwater, but it is time-consuming and labor-intensive and cannot obtain underwater geological information in the entire area; the electromagnetic waves emitted by ground-penetrating radar decay rapidly in water. Due to the limitation of detection depth, only limited geological information such as the underwater bedrock surface can be obtained, and high-precision detection of the lower geological information under water cannot be performed; transient electromagnetic has serious low-resistance shielding caused by low-resistance water bodies. High-precision transient electromagnetic can obtain underwater geological structures within a depth of thousands of meters, but it is difficult to accurately detect and resolve smaller targets in shallow geological bodies such as human underwater engineering construction; underwater sonar and seismic exploration have limited target resolution capabilities in sedimentary layers below the water surface, and it is difficult to effectively detect relatively small and hidden underwater targets; conventional electrical exploration is to copy the cables and acquisition instruments of ground electrical exploration to the water area for detection, which has the defects of low construction measurement efficiency, slow data acquisition, poor controllability, and low accuracy.

In view of the defects of conventional electrical exploration currently used in water areas, relevant technicians have made improvements. In the invention patent entitled A Water Area Electrical Exploration System with the authorization announcement number CN105259584B, it is disclosed that the transmitter outputs a variable current signal under the control of the main control platform and sends it underwater to generate an underwater electric field. Then, the multi-channel receiver receives the geoelectric voltage reflecting the geoelectric information at different depths through the electric field sensor and the underwater towed detection cable, and collects the transmission current of the transmitter and transmits it to the main control platform. Then, the main control platform obtains the geoelectric parameters reflecting the underwater geological conditions by receiving the signals of each channel of the multi-channel receiver, thereby completing the electrical exploration of freshwater areas.

Although the above patents have made certain improvements to different problems, they still do not systematically solve the following problems:

1) Underwater terrain fluctuations: Because the terrain fluctuations affect the later data results, if the cable system laid on the bottom of the water does not correct the elevation coordinates of each cable electrode according to the actual terrain, but only assumes that each cable electrode is located on the same horizontal plane for processing, then the data processing results without correcting the electrode elevation coordinates will be quite different from the results of the actual addition of the elevation coordinates, and cannot truly and accurately reflect the underwater geological information. Most of the cables designed in existing patents float on the water surface or at the same depth in the water. It does not take into account the differences in the underwater terrain fluctuations of the electrodes on each cable after the cable system is laid on the bottom of the water. Even if the cable is directly sunk to the bottom of the water for detection, it is not clearly pointed out that the underwater terrain fluctuations need to be considered and explained, and the elevation coordinates of each electrode on the cable need to be measured and obtained by sensors and brought into the processing software for terrain data processing and other operations.

2) Underwater cable dragging: The cable system sunk to the bottom of the water is directly coupled with the underwater soil medium through the simple underwater electrodes on the copper channel, and then the field data is collected. After the collection is completed, each electrode needs to be removed from the soil medium and then dragged forward by a tugboat to the next area to be measured for measurement. Among them, the dragging of underwater cables needs to first solve the problem of separating the cable electrodes from the underwater soil. In addition, if the cable system is directly dragged on the bottom of the water after the two are separated, there is a high possibility that there will be actual problems such as the cable structure being damaged by underwater foreign objects pulling the cable or the electrodes being inserted into the soil medium again due to the undulating underwater terrain and being unable to be directly dragged.

3) Underwater positioning of cables: The measurement of underwater geological bodies requires the positioning of cables. The purpose is to determine the actual control length of the cables during each acquisition and the position of the cables, and to provide actual coordinate positioning data for each cable movement and overlapping cable layout position, so as to improve the accuracy of on-site cable layout and data collection in strict accordance with the designed measurement line position and area. Underwater positioning of cables can solve the problems of deviation of the on-site cable position from the actual position each time it moves, and large errors in the measurement position points each time the cables move and overlap. The existing cable positioning only installs a positioning system at the head and tail electrodes to obtain the layout position of the cables, but does not take into account the starting point coordinates of the overlapping layout section after each movement of the cables. If the layout deviation is large, it will affect the accuracy of the results after the data of each section is jointly processed, and reduce the accuracy of underwater geological body detection.

Summary of the invention

In view of this, the present invention provides a towed underwater geological electrical detection system and method to systematically solve the above-mentioned shortcomings and problems that still exist in underwater geological electrical detection, and has good application prospects.

In order to achieve the above object, the present invention adopts the following technical solution:

A towed underwater geological electrical detection system, comprising: an underwater cable, a simple underwater electrode, a water pressure measurement sensor unit, a cable floating unit, an underwater GPS positioning system, an inflator, an electrical data acquisition storage module and a data processing module;

The underwater cable is fixed to the cable floating and sinking unit, and the cable floating and sinking unit is connected to the inflator; the underwater cable is sequentially connected to the electrical method data acquisition storage module and the data processing module;

A plurality of the simple underwater electrodes and a plurality of water pressure measuring sensor units are fixed on the underwater cable line; and the water pressure measuring sensor units and the simple underwater electrodes are arranged correspondingly;

The underwater GPS positioning system includes: a transponder, a ship-borne transducer and a GPS; wherein only three transponders are required, and the transponders are respectively fixed at the front, middle and tail simple underwater electrodes of the underwater cable; the transponder is wirelessly connected to the ship-borne transducer; and the GPS is fixed on the tugboat.

Preferably, the underwater cable is a special underwater geophysical exploration cable that is sealed, waterproof and has strong tensile strength, wherein each copper sheet channel on the cable is designed as a die-cast circular ring tap (copper ring).

Preferably, the cable floating and sinking unit comprises: a plurality of underwater air bags and snorkels;

Each of the underwater airbags is fixed one by one directly above each of the simple underwater electrodes; each of the underwater airbags is connected to each other through the ventilation tube, and the ventilation tube is connected to the inflator. The cable floating and sinking unit has the ability to control the cable line to float up and down in the water, and it is composed of an underwater airbag and a connecting tube with good shrinkage and expansion performance. Among them, the underwater airbag is designed to be directly above the simple underwater electrode fixed at the position of each copper ring on the cable line; each of the underwater airbags is connected to each other through the ventilation tube, and the sealing is intact; the cable floating and sinking unit and the underwater cable can be required to be bonded and fixed by the manufacturer before leaving the factory.

Preferably, it also includes: a water pressure display; the water pressure measurement sensor unit is connected to the water pressure display in a wireless manner.

The water pressure measuring sensor unit has a sealed and waterproof performance; the water pressure measuring sensor unit is fixed beside each copper ring of the underwater cable line, and is used to measure the water pressure at the depth of each electrode on the underwater cable line, and then calculate the depth of each electrode at the bottom of the water, and obtain the bottom terrain undulation data; each water pressure measuring sensor unit transmits the measured and calculated bottom depth data of each simple underwater electrode to the water pressure display on the tugboat through a wireless signal; the water pressure display is used to receive and save the measurement data transmitted back by each water pressure measuring sensor unit and can display it in real time.

Preferably, it also includes: a positioning display; the positioning display is placed on the tugboat; the ship-borne transducer is connected to the positioning display.

The underwater GPS positioning system consists of a ship-borne GPS, a ship-borne transducer, an underwater transponder and a positioning display; the ship-borne GPS and positioning display are placed on the ship; the ship-borne transducer is placed under the water near the stern; only three underwater transponders are needed, two of which are fixed on the cable at the head and tail electrodes of the underwater cable, and the other transponder is fixed at the cable position point where the cable is moved and overlapped each time according to the overlapping measurement section of the cable; the transponder fixed in the middle of the underwater cable can be adjusted and fixed before the cable is put into the water according to the actual overlapping range required;

Underwater GPS positioning technology is a combination of GPS positioning and hydroacoustic positioning. It uses hydroacoustic relative positioning technology to extend the high-precision positioning capability of GPS surface to underwater, so that the object to be measured can obtain its own latitude and longitude coordinates at the working depth, and the positioning accuracy can be guaranteed to be at the same order of magnitude as the GPS surface positioning accuracy. Ultra-short baseline (USBL) positioning technology is a type of hydroacoustic positioning technology, which is suitable for working in shallow waters. In the USBL system, the transponder is installed on the underwater cable line, and the ship-borne transducer completes the underwater cable line attitude positioning by measuring the horizontal and vertical angles and slant distance to the transponder. Underwater GPS positioning technology has the advantages of simple installation, easy operation, no need to set up an underwater baseline array, and high ranging accuracy.

The positioning data obtained by the ship-borne transducer measurement is sent to the positioning display through the CAN bus; the positioning display automatically calculates the underwater positioning data obtained by the ship-borne GPS and the ship-borne transducer measurement, and accurately determines the longitude and latitude coordinates of the first and last electrode points on each cable, the effective measurement length range of each underwater cable collected and laid, and the overlapping position points after the cable moves, so that the position of each cable system laid on the bottom of the water can be effectively controlled to move on the survey line in the area to be measured and the overlapping measurement range can be accurately controlled.

Preferably, according to the actual situation of laying underwater cables on the bottom of the water, the simple underwater electrodes include: dorsal fin-shaped underwater electrodes, arc-shaped underwater electrodes and pointed cone-shaped underwater electrodes.

The simple underwater electrode changes the existing rod-type electrode design style that is only applicable to the surface. According to the actual situation of the underwater cable being laid on the bottom of the water, the electrode is designed into a simple underwater electrode with multiple styles to choose from, such as dorsal fin, arc, and pointed cone. The dorsal fin and arc electrodes are suitable for soft contact surfaces such as muddy soil layers on the bottom of the water, and the pointed cone electrode is suitable for contact surfaces with larger or harder particles such as sand layers and gravel layers on the bottom of the water. Preferably, the simple underwater electrode is made of copper or other materials with excellent conductivity and is a solid structure, which can increase the weight of the cable. The simple underwater electrode is fixedly buckled on each copper ring channel of the above-mentioned cable. The simple underwater electrode has a simple structure, is easy to fix, is low in price, has a good contact coupling effect with the bottom soil medium, and has strong applicability.

Preferably, the inflator is a controllable inflator connected to the vent pipe in the cable floating unit through a gate valve. By controlling the inflator to inflate the vent pipe, the gas is gathered into each underwater airbag through the vent pipe, so that the underwater airbag is inflated and expanded, and the cable system is separated from the underwater soil medium and floats upward due to the buoyancy generated by the expansion of the airbag (wherein, the maximum buoyancy that can be generated after the airbag is inflated must allow the cable to float on the water surface as a whole). After the cable moves forward with the ship to the next measurement area, the underwater airbag is deflated so that the cable sinks to the bottom of the area to be measured and contacts the underwater soil medium. By inflating and deflating the underwater airbag with a controllable inflator, the cable system can be adjusted to different positions such as sinking to the bottom of the water, hanging in the water, or floating on the water surface.

Preferably, the simple underwater electrode has a plurality of conductive springs on the inner side, and each of the simple underwater electrodes is fixed to each copper sheet channel on the underwater cable line through a conductive spring.

Preferably, the position of the transponder at the simple underwater electrode located in the middle of the cable is determined based on the overlapping measurement positions after each movement of the underwater cable on the bottom of the water.

Preferably, the electrical data acquisition and storage module includes a network parallel electrical instrument; the underwater cable is connected to the data acquisition interface of the network parallel electrical instrument through a matching aviation plug; the network parallel electrical instrument has a parallel acquisition function of multiple electrode spacings for high-density electrical methods, and also has the function of continuous and rapid parallel scanning of the earth's electric field, which greatly improves the efficiency and data quality of on-site electrical data acquisition.

The data processing module is a laptop or desktop computer with corresponding data processing software preset; the data processing software includes: network parallel electrical method processing system software, Surfer mapping software, Excel and AGI inversion software.

A detection method based on a towed underwater geological electrical detection system comprises the following steps:

(1) Preparation

On the tugboat, a simple underwater electrode, a transponder, a water pressure measurement sensor unit and a cable floating unit are fixed on the corresponding positions of the underwater cable line to form an underwater cable system, and the underwater cable line is connected to the electrical method data acquisition storage module and the data processing module in turn;

Specifically, first fix the simple underwater electrodes on the copper rings of the cable, then fix a transponder at the corresponding electrode position in the middle of the cable according to the overlapping measurement range of the actual cable after each movement under water, insert the special aviation plug at the tail end of the cable into the data acquisition interface of the network parallel electrical instrument, connect the tail end ventilation pipe of the cable floating unit to the controllable inflator, fix the ship-borne GPS at the stern, and place the ship-borne transducer under the water at the stern. It should be noted that the cable floating unit, the water pressure measurement sensor unit fixed next to the copper rings of the cable, and the transponders fixed at the electrodes at the head and tail of the cable can all be installed and fixed at the corresponding positions on the underwater cable by the manufacturer before leaving the factory.

(2) Placing the underwater cable system on the bottom of the water

The underwater cable system is placed in water, and the inflator is used to inflate the cable floating and sinking unit, so that the underwater cable system floats below the water surface first. After the tugboat drags the underwater cable system to the location of the test area, the air volume of the underwater airbag in the cable floating and sinking unit is gradually released by the inflator, so that the underwater cable system gradually sinks. During this process, the underwater GPS positioning system can obtain the posture and position of the underwater cable in real time, and the water pressure measurement sensor unit measures the water depth of each simple underwater electrode. After the underwater cable system reaches the designated survey line position and sinks to the bottom of the water, so that the electrode is in full contact with the underwater soil medium, the underwater terrain data measured by the water pressure measurement sensor unit at the position of each simple underwater electrode and the longitude and latitude coordinates measured by the transponder at three positions of the first and last electrodes and the electrode at the overlapping starting point on the underwater cable line are obtained and saved;

(3) Collecting underwater geological electrical data

The parameters of the electrical data acquisition and storage module are set. After the setting is completed, power is supplied. Each copper sheet on the underwater cable generates current and forms an electric field in the underwater soil medium through a simple underwater electrode. At the same time, potential is collected to obtain the underwater geological electrical data in the monitoring section.

Specifically, first set the instrument acquisition parameters, such as constant current time, sampling time interval, power supply voltage, acquisition mode, power supply method, etc.; after the instrument parameters are set, power the instrument, and each copper sheet on the underwater cable line generates current and forms an electric field in the underwater soil medium through the electrodes in turn, and all other electrodes collect potentials, and finally obtain the underwater geological electrical data in the monitoring section. The network parallel electrical instrument is divided into two different acquisition modes: AM method (single-point power field) and ABM method (dipole power field). Among them, the AM acquisition mode can simultaneously collect electrical data of secondary and tripole device types (infinite electrodes need to be laid out), and the ABM acquisition mode can simultaneously collect electrical data of three types of devices, Wenner quadrupole, Wenner dipole and Wenner differential (no infinite electrodes need to be laid out). Under normal circumstances, the constant current time and sampling time interval of the AM acquisition mode are set to 0.5s and 50ms respectively; the constant current time and sampling time interval of the ABM acquisition mode are set to 0.2s and 100ms respectively.

(4) Drag to the next detection position and repeat the above steps

After the data collection is completed, the air in the vent pipe is inflated by the inflator, so that the underwater cable system floats upward with the expansion of the underwater airbag, and the simple underwater electrode is separated from the underwater soil medium and floats upward with the underwater cable system as a whole. The tugboat drags the underwater cable system as a whole to the direction of the next detection section. After reaching the designated area, the first electrode on the cable line is controlled at the starting point of the overlapping section, that is, the position coordinate point of the middle transponder during the last collection, through the underwater GPS positioning system. Then, the underwater airbag is gradually deflated to make the entire underwater cable system sink to the bottom of the water. After the underwater cable system is completely sunk to the bottom of the water and the simple underwater electrode is inserted into the underwater soil medium, the above data collection operation and the operation of moving and dragging the underwater cable system to the next detection area are repeated until the data collection in the entire test area is completed;

(5) Data processing stage

The data processing stage includes preprocessing, data inversion processing and data result mapping;

Preprocessing: Use the network parallel electrical method processing system software to open the original data; view and modify the simple underwater electrode coordinates, including operations such as converting and merging coordinate data in Excel software, adding terrain data, and exporting files; put the exported file data with terrain into the network parallel electrical method processing system, and merge the original data of each section; the next step is conventional data decoding, outputting apparent resistivity data files and AGI inversion format data files. Among them, the collected data needs to be checked before conventional data decoding, and if there are abnormal jump points in the data that do not conform to the actual situation, they need to be eliminated;

Data inversion processing: Select the appropriate inversion method based on the on-site geological conditions and the quality of actual data collection to obtain the best inversion results. The AGI inversion software provides three inversion methods, including damped least squares inversion, smooth model inversion and anti-noise inversion. The main process is: initial setting of inversion parameters, selection of appropriate inversion method, setting of data noise standard, number of inversion iterations, smooth coefficient and maximum root mean square error; opening the AGI inversion format data file and performing joint inversion to obtain the electrical data profile of the complete underwater geological body on the entire survey line. After the inversion is completed, export the inversion resistivity data file in dat format;

Data result mapping: The apparent resistivity data and the inversion resistivity data exported by the AGI inversion software are processed by the Surfer mapping software, including: opening the data in dat format in the Surfer software, gridding the data, selecting the gridding method, the grid division size and filtering the basic processing flow of abnormal data, and selecting the filter to filter the data and perform whitening processing according to actual needs. Through the above processing flow, the underwater geological electrical result map with terrain is finally obtained;

(6) Analysis of underwater geological electrical properties

According to the actual purpose of underwater detection and the detection results, and combined with the existing on-site geological data, the resistivity and distribution characteristics of different areas in the electrical result map are interpreted, and the underwater geological information is comprehensively analyzed and judged.

The towed underwater geological electrical detection system and method provided by the present invention have a wide range of applications and can perform high-precision and high-resolution rapid detection of underwater geology in shallow seas, rivers, lakes and reservoirs. Specifically, it can accurately explore underwater geology including: thickness of underwater silt layer, depth of underwater bedrock surface, structural integrity of underwater rock mass, stability of underwater foundation engineering, degree and scope of seawater intrusion, location of shallow underwater gas storage, karst cavities, fissure seepage channels, spatial distribution of goaf areas under water bodies in coal mines, and height of fissure zones of overlying rock masses on working surfaces, so as to obtain accurate and detailed geological information of underwater geological target bodies.

It can be seen from the above technical solutions that the present invention discloses a towed underwater geological electrical detection system and method. Compared with the prior art, the beneficial effects of the present invention are as follows:

1. The designed simple underwater electrode changes the defects of the traditional rod electrode that is sunk to the bottom of the water or floated on the water surface for detection, improves the contact coupling effect between the underwater cable and the underwater soil medium, and has the advantages of simple structure, convenient fixation, detachability, and strong applicability. The cable system with the simple underwater electrode fixed on it sinks to the bottom of the water, and the detection depth is deeper, the data resolution is higher, and the data results are more reliable.

2. It solves the practical problem that the previous water cable system does not take into account the undulations of the underwater terrain. The water depth of each electrode is measured through the water pressure measurement sensor unit, and the actual underwater terrain coordinates of each electrode are brought into the data processing software for processing. The result will be more real and reliable, and the location of the abnormal body will be more accurately delineated.

3. It solves the problems of the inability to accurately determine the position of the underwater cable on site, the unknown effective underwater measurement length of the cable, and the large deviation of the overlapping position points of the cable movement. The underwater GPS positioning system can accurately locate the actual position of the cable and the coordinates of the starting point of the overlapping position of the next station after the cable moves in real time. It can also grasp the posture of the cable system at the bottom of the water at all times, and control the layout and movement of the underwater cable to always be carried out on the measurement line.

4. The underwater airbag is inflated and deflated by a controllable inflator. The change in the buoyancy of the airbag drives the cable system to sink to the bottom of the water or float up and down in the water. The hull drags the cable to the next measurement area, which effectively solves the problem of how to detach and move the simple underwater electrode after it is inserted into the bottom soil medium for contact coupling when the towed cable system is laid on the bottom of the water.

5. The network parallel electrical instrument has the characteristics of a conventional high-density electrical instrument and the advantage of continuous, rapid and parallel scanning of the geoelectric field. Therefore, the network parallel electrical instrument and the intelligent integrated towed underwater geological electrical detection system are promoted and applied in the field of water area electrical detection, which can realize rapid and high-resolution scanning of underwater geological structures.

The towed underwater geological electrical detection system and method provided by the present invention systematically solve the problems and technical difficulties existing in the current electrical detection of water areas, and have broad application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

FIG1 is a schematic diagram of the overall structure of a towed underwater geological electrical detection system provided by the present invention;

FIG2 is a schematic diagram of the entire system floating up after the cable floating and sinking unit provided by the present invention is inflated;

FIG3 is a schematic diagram of the movement of a tugboat towing an underwater cable system provided by the present invention;

FIG4 is a schematic diagram of the arrangement of the underwater cable system provided by the present invention after reaching the next measurement section;

FIG5 is a front view of three types of simplified underwater electrodes provided by the present invention;

FIG6 is a side view of a simplified underwater electrode provided by the present invention;

FIG7 is a working principle diagram of a water pressure measurement module provided by the present invention;

FIG8 is a working principle diagram of the underwater GPS positioning system provided by the present invention;

FIG9 is a field workflow diagram of the towed underwater geological electrical detection system provided by the present invention;

FIG10 is an inversion resistivity profile of conventional water area electrical detection on the water surface;

Figure 11 is an inversion resistivity profile of conventional water area electrical method detection at 2.5m below the water surface;

FIG. 12 is an inversion resistivity profile diagram of the towed underwater geological electrical detection system provided by the present invention located on the surface of the underwater soil medium for detection.

In the figure, 1 is an underwater transponder, 2 is a simple underwater electrode, 3 is an underwater airbag, 4 is a water pressure measurement sensor unit, 5 is a voltage reference electrode N pole, 6 is a cable, 7 is a ventilating tube, 8 is a ship-borne transducer, 9 is a GPS, 10 is a CAN bus, 11 is a tugboat, 12 is a controllable inflator, 13 is a network parallel electrical instrument, 14 is a positioning display, 15 is a water pressure display, and 16 is a conductive reed.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Referring to FIG. 1 , FIG. 1 is a schematic diagram of the overall structure of the towed underwater geological electrical detection system provided by the present invention, which specifically includes: an underwater cable 6, a simple underwater electrode 2, a water pressure measurement sensor unit 4, a cable floating unit, an underwater GPS positioning system, an inflator 12, an electrical data acquisition storage module and a data processing module;

The underwater cable 6 is fixed to the cable floating and sinking unit, and the cable floating and sinking unit is connected to the inflator 12; the underwater cable 6 is connected to the electrical method data acquisition storage module and the data processing module in sequence;

A plurality of simple underwater electrodes 2 and a plurality of water pressure measuring sensor units 4 are fixed on the underwater cable 6; and the water pressure measuring sensor units 4 and the simple underwater electrodes 2 are arranged correspondingly;

The underwater GPS positioning system includes: a transponder 1, a ship-borne transducer 8 and a GPS 9; only three transponders 1 are required, which are respectively fixed on the front, middle and tail simple underwater electrodes 2 on the underwater cable 6; the transponder 1 is wirelessly connected to the ship-borne transducer 8; and the GPS 9 is fixed on the tugboat 11.

In the specific implementation, the underwater cable 6 is glued and fixed to the cable floating and sinking unit, and the underwater cable 6 is connected to the data interface of the electrical data acquisition and storage module through the aerial plug. Specifically, the electrical data acquisition and storage module is a network parallel electrical instrument 13; the network parallel electrical instrument 13 is connected to the data processing module.

The simple underwater electrode 2 is fixed to each copper sheet channel on the underwater cable 6; the water pressure measurement sensor unit 4 is fixedly installed on the underwater cable 6 next to the simple underwater electrode 2; the transponder 1 in the underwater GPS positioning system is fixed at the front, middle and tail electrodes on the underwater cable 6; the ship-borne transducer 8 in the underwater GPS positioning system is suspended at the tail of the tugboat 11 and placed below the water surface; the GPS9 in the underwater GPS positioning system is fixed at the tail of the tugboat 11; the network parallel electrical instrument 13, the data processing module, the inflator 12, the water pressure display 15, the GPS 9 and the matching positioning display are placed on the tugboat 11; wherein, the water pressure measurement sensor unit 4 is connected to the water pressure display 15 by wireless means; the ship-borne transducer 8 is connected to the positioning display 14. The underwater cable 6, the simple underwater electrode 2, the transponder 1, the water pressure measurement sensor unit 4 and the cable floating and sinking unit are integrated into one and placed on the bottom of the water.

In order to further optimize the above technical solution, the cable floating and sinking unit includes: multiple underwater airbags 3 and ventilation tubes 7; each underwater airbag 3 is fixed one by one directly above each simple underwater electrode 2; each underwater airbag 3 is connected through the ventilation tube 7, and the ventilation tube 7 is connected to the inflator 12.

According to the actual situation that the underwater cable 6 is laid on the bottom of the water, the simple underwater electrode 2 includes: a dorsal fin underwater electrode, an arc-shaped underwater electrode and a pointed cone-shaped underwater electrode. Please refer to Figure 5, Figure 5a is a dorsal fin underwater electrode, Figure 5b is an arc-shaped underwater electrode, and Figure 5c is a pointed cone-shaped underwater electrode. The dorsal fin-shaped and arc-shaped electrodes are suitable for soft contact surfaces such as muddy soil layers on the bottom of the water, and the pointed cone-shaped electrode is suitable for contact surfaces with larger or harder particles such as sand layers and gravel layers on the bottom of the water. Please refer to Figure 6, the simple underwater electrode has a conductive spring 16, wherein the conductive spring 16 is a conductive spring with a certain deformation and clamping and fixing ability that can clamp and fix the simple underwater electrode 2 on the copper sheet of the cable, that is, the simple underwater electrode 2 is fixed to each copper sheet channel on the underwater cable 6 through the conductive spring 16.

Preferably, the inflator 12 is a controllable inflator 12 connected to the vent pipe 7 in the cable floating unit through a valve. By controlling the inflator to inflate the vent pipe, the gas is gathered into each underwater airbag through the vent pipe, so that the underwater airbag is inflated and expanded, and the cable system is separated from the underwater soil medium and floats upward due to the buoyancy generated by the expansion of the airbag (wherein, the maximum buoyancy that can be generated after the airbag is inflated must allow the cable to float on the water surface as a whole). After the cable moves forward with the ship to the next measurement area, the underwater airbag is deflated so that the cable sinks to the bottom of the area to be measured and contacts the underwater soil medium. By inflating and deflating the underwater airbag with a controllable inflator, the cable system can be adjusted to different positions such as sinking to the bottom of the water, hanging in the water, or floating on the water surface.

Refer to Figure 7, which is a schematic diagram of the working of the water pressure measurement module provided by the present invention, wherein the water pressure measurement sensor unit 4 is installed and fixed at each copper sheet position on the cable 6, and is used to measure the water depth of each simple underwater electrode 2, and obtain the bottom terrain data. By operating the water pressure display 15, the water pressure measurement sensor unit 4 is controlled in real time to obtain the bottom terrain data and transmit the data wirelessly to the water pressure display 15.

Fig. 8 is a working principle diagram of the underwater GPS positioning system provided by the present invention. Specifically, the underwater GPS positioning system is composed of a ship-borne GPS 9, a ship-borne transducer 8, an underwater transponder 1 and a positioning display 14; the ship-borne GPS 9 and the positioning display 14 are placed on the ship; the ship-borne transducer 8 is placed under the water near the stern; the underwater transponders 1 only need three, two of which are respectively fixed on the cable at the head and tail electrodes of the underwater cable, and the other transponder is fixed at the cable position point where the cable is moved and overlapped each time according to the cable overlap measurement section; the transponder fixed in the middle of the underwater cable can be adjusted and fixed before the cable is submerged according to the actual overlap range required. The design of this system is suitable for accurately positioning the attitude, position and overlapping measurement starting point of the underwater cable, and provides accurate positioning data by moving and determining the position of the cable on site each time, providing a more reliable guarantee for the merging and processing of the later data.

In the overall structure of the towed underwater geological electrical detection system provided by the present invention, the spacing and number of annular copper sheets designed according to a certain electrode spacing on the cable line, and the position of the N pole (annular copper sheet) of the voltage reference electrode can be customized by the manufacturer according to actual needs. The transponders between the snorkel at the top of the cable line and the underwater airbag, between the snorkel, the underwater airbag and the cable line, and each water pressure measurement sensor unit and the first and last electrodes of the cable line are processed and integrated into one by the manufacturer according to customer needs before leaving the factory. The above-mentioned components and structures do not need to be fixed by on-site staff. The on-site staff only need to fix an underwater transponder at the corresponding position on the cable line and clamp and fix the simple underwater electrode at each annular copper sheet on the cable line to complete the on-site installation of the underwater cable system. After the underwater cable system is installed, the snorkel is connected to the controllable inflator, the cable line navigation plug is connected to the network parallel electrical instrument interface, and the ship-borne transducer is connected to the positioning display interface through the CAN bus to complete the connection and fixation of the entire system.

The towed underwater geological electrical detection system designed by the present invention has a wide range of applications. It can conduct high-precision and high-resolution rapid detection of underwater geology in shallow seas, rivers, lakes and reservoirs, etc. Specifically, it can accurately explore underwater geology including: thickness of underwater mud layer, depth of underwater bedrock surface, structural integrity of underwater rock mass, stability of underwater foundation engineering, degree and range of seawater intrusion, location of shallow underwater gas, karst cavities, fissure leakage channels, spatial distribution of goafs under water bodies in coal mines, and height of fissure zones of overlying rock masses on the working surface, etc., to obtain accurate and detailed geological information of underwater geological targets. According to the different depths and sizes of the detection targets, the electrode spacing and number of electrode channels of the production cable can be flexibly designed. For example, for geological structure detection at a depth of less than 10m under water, the cable can be designed with an electrode spacing of 1m and 32 electrode channels or an electrode spacing of 1m and 64 electrode channels, etc.; for geological structure detection at a depth of less than 50m under water, the cable can be designed with an electrode spacing of 2.5m and 64 electrode channels; and for geological anomaly detection such as goaf below the water body at a depth of 150m under water, overlying rock destruction on the coal mining face, etc., the cable needs to be designed with an electrode spacing of 5m and 64 electrode channels or an electrode spacing of 5m and 96 electrode channels, etc. Compared with the existing water area cable system, the present invention directly lays the cable system at the bottom of the water so that the simple underwater electrode is in direct contact and good coupling with the bottom soil medium, and can measure the bottom undulating terrain at each electrode. The intelligent integrated cable system has the obvious advantages of reliable data quality, deeper exploration depth, higher exploration accuracy, and wider application range.

The electrical method data acquisition storage module used in the present invention includes a network parallel electrical method instrument 13; the underwater cable 6 is connected to the data acquisition interface of the network parallel electrical method instrument 13 through a matching navigation plug;

The data processing module is a laptop or desktop computer with corresponding data processing software pre-installed; the data processing software includes: network parallel electrical method processing system software, Surfer mapping software, Excel and AGI inversion software.

The parallel electrical acquisition system has the parallel acquisition function of multiple electrode spacing of high-density electrical method, and also has the function of continuous and fast parallel scanning of the earth electric field, which greatly improves the efficiency and quality of electrical data acquisition. The electrical acquisition instrument has five power supply voltages of 0, 24, 48, 72, and 96V to choose from. The site can make reasonable choices according to the depth of the detection target, cable length, etc., and the instrument can set some electrodes on the control cable line to perform data acquisition according to the needs of the site, which is highly flexible. The instrument is divided into two acquisition modes, AM and ABM. Among them, the AM acquisition mode can simultaneously collect electrical data of secondary and tripole device types (infinite electrodes need to be laid out), and the ABM acquisition mode can simultaneously collect electrical data of three types of devices, Wenner quadrupole, Wenner dipole and Wenner differential (no infinite electrodes need to be laid out). Under normal circumstances, the constant current time and sampling time interval of the AM acquisition mode are set to 0.5s and 50ms respectively; the constant current time and sampling time interval of the ABM acquisition mode are set to 0.2s and 100ms respectively. Taking the case of 64 electrodes on a cable as an example, the acquisition time required for the AM acquisition mode is only 96 seconds, while the acquisition time required for the ABM acquisition mode is 1080 seconds. The amount of data collected by the ABM method is large, but compared with the AM method, the time required for on-site acquisition is too long, and it is difficult to meet the needs of rapid on-site detection. Therefore, on the basis of ensuring data reliability, it is more appropriate to choose the AM method as the on-site electrical data acquisition mode. Moreover, the use of the AM method for data acquisition on-site can satisfy the requirements of rapid electric field scanning while still being able to derive the AM method data into the ABM method data through post-processing, so that more electrical device data can be provided on the basis of efficient and rapid acquisition.

In addition, referring to FIGS. 1 to 4 and 9 , the embodiment of the present invention further discloses a detection method based on a towed underwater geological electrical detection system, comprising the following steps:

(1) Preparation

On the tugboat, a simple underwater electrode, a transponder, a water pressure measurement sensor unit and a cable floating unit are fixed on the corresponding positions of the underwater cable line to form an underwater cable system, and the underwater cable line is connected to the electrical method data acquisition storage module and the data processing module in turn;

Referring to Figure 1, there are 8 electrode channels on the cable line in Figure 1, which are 1# to 8# electrodes from left to right. First, the simple underwater electrodes 2 are fixedly buckled on the copper rings of the cable line 6 respectively, and then according to the overlapping measurement range of the actual cable after each movement on the bottom of the water, a transponder 1 is fixed at the corresponding electrode (6# electrode) position in the middle of the cable line 6, and the special navigation plug at the tail end of the cable line 6 is inserted into the data acquisition interface of the network parallel electrical method instrument 13, the tail end ventilation pipe 7 of the cable floating and sinking unit is connected to the controllable inflator 12, the ship-borne GPS 9 is fixed at the stern, and the ship-borne transducer 8 is placed under the water surface at the stern. It should be noted that the water pressure measuring sensor unit 4 fixed on the cable line 6 next to each copper ring of the cable line and a transponder 1 fixedly installed at the head (1# electrode) and tail (8# electrode) electrodes of the cable line 6 are fixedly installed by the manufacturer before leaving the factory. The underwater airbag is connected to the ventilation tube and glued to the upper part of the cable line 6, and the gluing and fixing of the cable floating and sinking unit is completed by the manufacturer.

(2) Placing the underwater cable system on the bottom of the water

The underwater cable system is placed in water, and the inflator is used to inflate the cable floating and sinking unit, so that the underwater cable system floats below the water surface first. After the tugboat drags the underwater cable system to the location of the test area, the air volume of the underwater airbag in the cable floating and sinking unit is gradually released by the inflator, so that the underwater cable system gradually sinks. During this process, the underwater GPS positioning system can obtain the posture and position of the underwater cable in real time, and the water pressure measurement sensor unit measures the water depth of each simple underwater electrode. After the underwater cable system reaches the designated survey line position and the electrode is in full contact with the underwater soil medium, the underwater terrain data measured by the water pressure measurement sensor unit at the position of each simple underwater electrode and the longitude and latitude coordinates measured by the transponder at three positions of the head and tail electrodes and the electrode at the overlapping starting point on the underwater cable line are obtained and saved;

Specifically, after the debugging of each unit module is completed, the underwater cable system is placed in water. At this time, the inflator 12 inflates the underwater airbag 3 through the vent pipe 7, and the underwater cable system is first floated below the water surface. After the tugboat 11 drags the underwater cable system to the measuring line position of the area to be measured, the air volume of the underwater airbag 3 is controlled and gradually released by the controllable inflator 12, so that the underwater cable system gradually sinks to the bottom of the water by its own weight. In this process, the data obtained by the underwater GPS positioning system can be displayed in real time on the positioning display 14, and the posture and position of the cable line are obtained. The water pressure measurement sensor unit 4 can measure the water depth of each electrode in real time. After the underwater cable system reaches the designated measuring line position and the electrode is completely in contact with the underwater soil medium, the underwater terrain data measured by the water pressure measurement sensor unit 4 at each electrode position is obtained and saved, and the terrain undulation data is wirelessly transmitted and saved in the water pressure display 15 on the tugboat 11, and the longitude and latitude coordinates of the three positions of the head and tail electrodes and the electrode at the overlapping starting point on the underwater cable line are obtained. The overall arrangement diagram of the underwater cable system after it sinks to the bottom of the water and each electrode is in contact and coupled with the bottom soil medium is shown in FIG1 .

(3) Collecting underwater geological electrical data

The parameters of the electrical data acquisition and storage module are set. After the setting is completed, power is supplied. Each copper sheet on the underwater cable generates current and forms an electric field in the underwater soil medium through a simple underwater electrode, and potential is collected to obtain the underwater geological electrical data in the monitoring section.

Specifically, the instrument parameters are first set, such as constant current time, sampling time interval, power supply voltage, acquisition mode, power supply method, etc. After the instrument parameters are set, the instrument is powered on, and each copper sheet on the underwater cable 6 generates current and forms an electric field in the underwater soil medium through the electrode 2 in turn, and all other electrodes collect potentials, and finally obtain the underwater geological electrical data in the monitoring section. The network parallel electrical instrument is divided into two different acquisition modes: AM method (single-point power field) and ABM method (dipole power field). Among them, the AM acquisition mode can simultaneously collect electrical data of secondary and tripole device types (infinite electrodes need to be arranged), and the ABM acquisition mode can simultaneously collect electrical data of three types of devices: Wenner quadrupole, Wenner dipole and Wenner differential (no infinite electrodes need to be arranged). Under normal circumstances, the constant current time and sampling time interval of the AM acquisition mode are set to: 0.5s, 50ms respectively; the constant current time and sampling time interval of the ABM acquisition mode are set to: 0.2s, 100ms respectively.

(4) Drag to the next detection position and repeat the above steps

After the data collection is completed, the air in the snorkel is inflated by the inflator, so that the underwater cable system floats upward with the expansion of the underwater airbag, and at the same time, the simple underwater electrode is driven to separate from the underwater soil medium and float upward with the underwater cable system as a whole. The tugboat drags the underwater cable system as a whole to the direction of the next detection section. After arriving at the designated area, the first electrode on the cable line is controlled at the starting point of the overlapping section, that is, the position coordinate point of the middle transponder during the last collection, through the underwater GPS positioning system. Then, the underwater airbag is gradually deflated to make the entire underwater cable system sink to the bottom of the water. After the underwater cable system is completely sunk to the bottom of the water and the simple underwater electrode is inserted into the underwater soil medium, the above data collection operation and the operation of moving and dragging the underwater cable system to the next test area are repeated until the data collection in the entire detection area is completed;

Specifically, it includes: after the data collection is completed, the controllable inflator 12 is used to inflate the vent pipe 7, so that the underwater airbag 3 on the cable line 6 expands, and the simple underwater electrode 2 is separated from the underwater soil medium and floats upward with the underwater cable system as a whole after the upward buoyancy of the airbag 3 gradually increases. The tugboat 11 drags the underwater cable system as a whole to the next detection section. After reaching the designated area, the cable line 1# electrode is controlled at the starting point of the overlapping section (i.e., the measurement repetition starting point where the 6# electrode is located in Figure 2) through the underwater GPS positioning system, and then the airbag 3 is gradually deflated, so that the entire cable system gradually sinks into the designated area at the bottom of the water. After the cable system is completely sunk to the bottom of the water and the simple underwater electrode is inserted into the underwater soil medium, the above data collection operation and the operation of moving and dragging the cable system to the next test area are repeated. See the schematic diagrams of Figures 3 and 4 for details.

(5) Data processing stage

The data processing stage includes preprocessing, data inversion processing and data result mapping;

The preprocessing process includes: using the network parallel electrical processing system (WBD Pro) to open the original data; checking and modifying the electrode coordinates, including operations such as converting and merging the coordinate data in Excel software, adding terrain data, and exporting files; putting the exported file data with terrain into the WBD Pro processing system, and merging the original data of each section; the next step is conventional data decoding, outputting the apparent resistivity data file (dat format), and outputting the AGI inversion format data file (urf format). Among them, the collected data needs to be checked before conventional data decoding. If there are abnormal jump points in the data that do not conform to the actual situation, they need to be eliminated to reduce the impact on the real data during the subsequent software calculation and inversion, and improve the data quality.

Data inversion processing flow, AGI inversion software provides three inversion methods, including damped least squares inversion, smooth model inversion, and anti-noise inversion. During inversion processing, you can choose the appropriate inversion method based on the on-site geological conditions and the quality of actual data acquisition to get the best inversion results. The main process is: initial setting of inversion parameters, selection of appropriate inversion method, setting of data noise standard, number of inversion iterations, smoothness coefficient, maximum root mean square error and other parameters. Open the urf format file to be inverted, and perform joint inversion after the above settings are completed to obtain the electrical data profile of the complete underwater geological body on the entire survey line. After the inversion is completed, export the inversion resistivity data file in dat format.

The data results are mapped, and the apparent resistivity data and the inversion resistivity data exported by the AGI inversion software are processed by the Surfer mapping software. This includes: opening the data in dat format in the Surfer software, gridding the data, selecting the gridding method, the grid division size, and filtering the basic processing flow of abnormal data. According to actual needs, a filter can be selected to filter the data and perform whitening and other processing. Through the above processing flow, the bottom geological electrical result map with terrain is finally obtained.

(7) Analysis of underwater geological electrical properties

The towed underwater geological electrical detection system and method designed by the present invention has a wide range of applications, and can be used for high-precision, high-resolution rapid detection of underwater geology in shallow seas, rivers, lakes and reservoirs, etc. Specifically, it can accurately explore underwater geology including: thickness of underwater mud layer, depth of underwater bedrock surface, structural integrity of underwater rock mass, stability of underwater foundation engineering, degree and range of seawater intrusion, location of shallow underwater gas, karst cavities, fissure seepage channels, spatial distribution of goafs under water bodies in coal mines, and height of fissure zones of overlying rock masses on the working surface, etc., to obtain accurate and detailed geological information of underwater geological targets. According to the actual underwater detection purpose and detection result map, and combined with the existing on-site geological data, the resistivity and distribution law characteristics of different regional positions in the electrical result map are interpreted, and the underwater geological information is comprehensively analyzed and judged.

The present invention clearly proposes and designs a set of intelligent underwater geological exploration towing cable system. Compared with other inventions that lay cables on the water surface or in water, the present invention lays the cable system directly on the bottom of the water and directly contacts and couples the electrodes on the cable with soil media such as the bottom mud layer, measures the water depth of each electrode through a water pressure measurement module, obtains the real undulating terrain data of the bottom of the water, and brings the coordinates of each electrode into the data processing software for topographic apparent resistivity mapping and topographic resistivity inversion, which significantly improves the accuracy and reliability of on-site detection data, makes the data results more in line with the actual situation, and also increases the effective detection depth of the cable system to the bottom geological body. In addition, through the underwater GPS positioning system, the longitude and latitude coordinates of the first and last electrode points on each cable, the effective measurement length range of the cable collected and laid each time, and the overlapping position points of the cable after movement are accurately determined, so that the position of each cable system laid on the bottom of the water is effectively controlled to perform mobile overlapping measurement on the survey line in the area to be measured. Finally, the original electrical data collected after each mobile layout are merged and jointly processed to obtain the electrical data profile of the complete bottom geological body on the entire survey line.

The present invention designs the cable system according to the actual problems and needs on site, and describes in detail the structural design, on-site layout, water bottom depth and terrain data collection of the electrodes, determination of the latitude and longitude coordinates of the first and last electrodes of the survey line and the overlapping electrode points, setting of on-site instrument parameters, data collection method, and after the collection is completed, an external controllable inflator inflates each underwater airbag through a ventilation pipe to make the entire cable system float (the floating position is controllable), after the hull moves to the next measuring section, the 1# electrode on the cable is controlled above the overlapping point, the airbag is deflated to make the cable system slowly sink to the area to be measured, and in this process, the cable line needs to be controlled and appropriately adjusted in the measuring section to reduce errors, and the above steps are repeated for data collection.

The present invention solves the problem that the electrodes are directly in contact and coupled with the soil after the cable system is laid on the bottom of the water. There is no need to design and install traditional stick-type electrodes that are only applicable to the ground and water electrodes with complex design structures and cumbersome on-site installation and layout. Compared with the detection of cables floating on the water surface and in the water, the present invention has obvious advantages such as more reliable detection data quality, more accurate data results, and deeper detection depth. It solves the actual problem that the water cable system invented before does not take into account the undulations of the bottom terrain. The water pressure measurement sensor unit is used to measure the depth of the electrode, and the actual bottom terrain coordinates of each electrode are brought into the data processing software for processing. The processing makes the results more real and reliable; it solves the problems of the inability to accurately determine the underwater cable position on site, the unknown actual effective measurement length of the cable, and the large deviation of the overlapping position points of the cable movement. The underwater GPS positioning system is used to accurately locate the actual position of the cable and the overlapping position points of the next station after the cable moves, and the posture and movement of the underwater cable are always controlled to be on the survey line; it solves the problem of how to move the towed cable system after it is laid on the bottom of the water so that the simple underwater electrode contacts and couples with the underwater medium. By inflating the underwater airbag, the cable system is driven to float up, and then the cable is towed to the next measurement area through the hull.

It should be noted that the cable system designed by the present invention is mainly sunk to the bottom of the water so that the simple underwater electrode is in direct contact with the soil medium such as the silt layer with undulating terrain on the bottom of the water for coupling and detection, thereby improving the accuracy of the exploration data and the exploration depth. However, the cable system of the present invention is not limited to being used only for geological exploration on the bottom of the water. The present invention inflates the underwater airbag through an external controllable inflator, so that the entire cable system can float in the water and at any position on the water surface for detection, and obtains accurate data such as the depth and position of the cable system in the water through the underwater GPS positioning system and the water pressure measurement sensor unit. Therefore, in the process of detecting underwater geology on site, if there are many foreign objects on the bottom of some areas that interfere with the layout of the cable system, and it is not convenient to sink the cable system to the bottom of the water, the cable system can be floated in the water or at any position on the water surface in the above manner, and then the field data can be collected. It should be noted that the depth of each electrode when the cable system floats in the water is not required to be controlled at the same depth. The water pressure measurement module at each electrode position can obtain the water depth in real time. During the data processing, the electrode coordinate data with the electrode elevation is brought into the processing software for processing. Therefore, the present invention can adjust the cable system to sink to the bottom of the water or float in the water or on the water surface in a timely manner according to different geological conditions, complex terrain conditions or external interference conditions at the bottom of the water. Therefore, the field applicability of the present invention is stronger. While meeting the focus on directly detecting underwater geology, it also takes into account the design and has the ability to quickly scan and detect at any depth floating in the water or on the water surface.

In order to compare and verify that the detection of the technical solution provided by the present invention is more accurate and has better effect than the current water body electrical detection, a field comparative detection experiment was carried out in a certain river channel. Attached Figures 10 and 11 are the resistivity profiles inverted by the detection results of the cable at the water surface and 2.5m below the water surface respectively using a conventional water body electrical detection system, and attached Figure 12 is the inversion resistivity profile of the detection on the surface of the underwater soil medium using the towed underwater geological electrical detection system provided by the present invention. Among them, the electrode spacing on the cable used in the three groups of profiles is 1m, the number of electrode channels is 64, and 16 electrodes overlap between the measuring lines. A network parallel electrical instrument is used to collect the on-site underwater electrical data, and the instrument power supply voltage is 72V, and AM method data collection is performed.

From the analysis of Figure 10, it can be found that since the cable system is laid on the water surface, the electric field generated in the test area after the instrument is powered on is mainly distributed in the water body due to the low-resistance shielding effect of the water body, while the electric field entering the inner part of the underwater geological body is relatively weak, which makes it impossible to effectively obtain the electrical data of the underwater geology. However, from the figure, the distribution of the underwater interface and the underwater topography can be seen in the result diagram, but the structure of the underwater geological body cannot be effectively judged. The detection result does not meet the requirements for the exploration of the internal structure of the underwater geology, but can detect basic information such as the distribution of the underwater interface. In addition, the depth below the water that can be effectively detected is limited.

Analysis of Figure 11 shows that the result of placing the cable system 2.5m below the water surface for detection is better than that of placing it on the water surface. The location of the underwater geological anomaly can be better delineated. The dark area in the figure is the underwater bedrock, and the white area is the distribution location of soil media such as silt. It can be found from the figure that there is a white low-resistance area inside the bedrock in the horizontal range of 55 to 80m and the depth of 8 to 16m. Analysis shows that the bedrock integrity in this area may be poor, and long-term water erosion has caused a large amount of silt and other soil media to be filled in this location.

In order to compare the difference in effect and accuracy between the detection of the present invention and the above two detection methods, the towed underwater geological electrical detection system of the present invention was used in the same test area. The simple underwater electrode was inserted into the underwater medium due to its own weight and the weight of the cable system, and then the coupling was good for field detection. Since the cable system was arranged on the underwater interface, there was a certain terrain undulation on the bottom of the water, so the effective detection length in the horizontal direction would be slightly shorter than the above two methods. After the collected data was processed accordingly, the resistivity profile with underwater terrain inversion as shown in Figure 12 was obtained. The thickness of the underwater silt layer at different positions and the position of the underwater bedrock interface can be clearly distinguished from the figure. The white area in the figure is the distribution of soil media such as the underwater silt layer, and the dark area is the underwater bedrock medium. It can be seen from Figure 12 that there is a low-resistance area similar to a gap at the bedrock surface at a position of 50 to 55 meters in the horizontal direction, and below the gap, there is a low-resistance area of 45 to 75 meters in the horizontal direction and 9 to 1 meters in the vertical direction. The low-resistance area within the range of 5m is connected, and the resistivity of the area is basically 5-20Ω〃m, which is close to the resistivity value of the silt layer above the bedrock surface. It is analyzed that the stability and integrity of the underwater bedrock at this location are poor, and the low-resistance area in the bedrock is partially filled with a large amount of silt and water, and the upper part of the bedrock of the low-resistance area is in a suspended state. Therefore, if the pile body or other engineering construction is carried out at this location without effectively exploring the underwater geology of the area, it will seriously affect the stability and safety of the later engineering structure. In order to verify the accuracy of the detection results of the system of the present invention, the on-site drilling team drilled and verified at two positions of 55m and 70m in the horizontal direction of the test area. According to the comparison of the drilling results with Figure 12, it is found that the results are basically consistent, and the on-site detection results are accurate and reliable. However, the results of the above two detection methods are compared with the detection results of the system of the present invention. It is found that the above two results cannot achieve this resolution and accuracy. At the same time, the effective detection depth for the underwater geological body is also shallow, and it is difficult to provide accurate underwater geological data and reliable guidance for the engineering construction in this area. Therefore, the system and method of the present invention have obvious advantages over the prior art.

In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims (7)

1. A towed underwater geological electrical detection system, characterized in that it includes: underwater cables, simple underwater electrodes, water pressure measurement sensor units, cable floating and sinking units, underwater GPS positioning systems, inflators, electrical data acquisition and storage modules, and data processing modules; The underwater cable is fixed to the cable floating and sinking unit, and the cable floating and sinking unit is connected to the inflator; the underwater cable is sequentially connected to the electrical method data acquisition storage module and the data processing module; A plurality of the simple underwater electrodes and a plurality of water pressure measuring sensor units are fixed on the underwater cable line; and the water pressure measuring sensor units and the simple underwater electrodes are arranged correspondingly; The underwater GPS positioning system comprises: a transponder, a ship-borne transducer and a GPS; the transponders are respectively fixed to the front, middle and tail simple underwater electrodes of the underwater cable; the transponder is wirelessly connected to the ship-borne transducer; the GPS is fixed on the tugboat; According to the actual situation of underwater cables being laid on the bottom of the water, the simple underwater electrodes include: dorsal fin-shaped underwater electrodes, arc-shaped underwater electrodes and pointed cone-shaped underwater electrodes; The simple underwater electrode has a plurality of conductive springs on the inner side, and each of the simple underwater electrodes is fixed to each copper sheet channel on the underwater cable line through the conductive springs; The transponder at the simple underwater electrode located in the middle is fixed on the cable, and its position is determined according to the overlapping measurement position after each movement of the underwater cable on the bottom of the water. 2. A towed underwater geological electrical detection system according to claim 1, characterized in that the cable floating and sinking unit comprises: a plurality of underwater air bags and ventilating tubes; Each of the underwater airbags is fixed one by one on the cable line just above each of the simple underwater electrodes; each of the underwater airbags is connected through the ventilation pipe, and the ventilation pipe is connected to the inflator. 3. A towed underwater geological electrical detection system according to claim 1, characterized in that it also includes: a water pressure display; the water pressure measurement sensor unit is connected to the water pressure display via wireless transmission. 4. A towed underwater geological electrical detection system according to claim 1, characterized in that it also includes: a positioning display; the positioning display is placed on the tugboat; the ship-borne transducer is connected to the positioning display. 5. A towed underwater geological electrical detection system according to claim 1, characterized in that the inflator is a controllable inflator connected to the ventilation pipe in the cable floating and sinking unit through a valve. 6. A towed underwater geological electrical detection system according to any one of claims 1 to 5, characterized in that the electrical data acquisition and storage module comprises a network parallel electrical instrument; the underwater cable is connected to the data acquisition interface of the network parallel electrical instrument through a matching aviation plug; The data processing module is a laptop or desktop computer with corresponding data processing software preset; the data processing software includes: network parallel electrical method processing system software, Surfer mapping software, Excel and AGI inversion software. 7. A detection method based on a towed underwater geological electrical detection system, characterized in that the method uses a towed underwater geological electrical detection system as described in any one of claims 1 to 6 to perform underwater geological detection, comprising the following steps: (1) Preparation On the tugboat, a simple underwater electrode, a transponder, a water pressure measurement sensor unit and a cable floating and sinking unit are fixed on the corresponding positions of the underwater cable line to form an underwater cable system, and the underwater cable line is connected to the electrical method data acquisition storage module and the data processing module in turn; (2) Placing the underwater cable system on the bottom of the water The underwater cable system is placed in water, and the inflator is used to inflate the cable floating and sinking unit, so that the underwater cable system floats below the water surface first. After the tugboat drags the underwater cable system to the location of the test area, the air volume of the underwater airbag in the cable floating and sinking unit is gradually released by the inflator, so that the underwater cable system gradually sinks. During this process, the underwater GPS positioning system obtains the posture and position of the underwater cable in real time, and the water pressure measurement sensor unit measures the water depth of each simple underwater electrode. After the underwater cable system reaches the designated survey line position and sinks to the bottom of the water, so that the electrode is in full contact with the underwater soil medium, the underwater terrain data measured by the water pressure measurement sensor unit at the position of each simple underwater electrode and the longitude and latitude coordinates obtained by the transponder at three positions of the first and last electrodes and the electrode at the overlapping starting point on the underwater cable line are obtained and saved; (3) Collecting underwater geological electrical data The parameters of the electrical data acquisition and storage module are set. After the setting is completed, power is supplied. Each copper sheet on the underwater cable generates current and forms an electric field in the underwater soil medium through a simple underwater electrode. At the same time, potential is collected to obtain the underwater geological electrical data in the monitoring section. (4) Drag to the next detection position and repeat the above steps After the data collection is completed, the air in the snorkel is inflated by the inflator, and the underwater airbag gradually expands, so that the simple underwater electrode is separated from the underwater soil medium and floats upward with the underwater cable system as a whole. The tugboat drags the underwater cable system as a whole to the direction of the next detection section. After reaching the designated area, the first electrode on the cable line is controlled at the starting point of the overlapping section, that is, the position coordinate point of the middle transponder during the last collection, through the underwater GPS positioning system. Then, the underwater airbag is gradually deflated to make the entire underwater cable system sink to the bottom of the water. After the underwater cable system is completely sunk to the bottom of the water and the simple underwater electrode is inserted into the underwater soil medium, the above data collection operation and the operation of moving and dragging the underwater cable system to the next detection area are repeated until the data collection in the entire test area is completed; (5) Data processing stage The data processing stage includes preprocessing, data inversion processing and data result mapping; preprocessing: use the network parallel electrical method processing system software to open the original data; view and modify the simple underwater electrode coordinates, including the operations of converting, collating and merging the coordinate data in Excel software, adding terrain data, and exporting files; put the exported file data with terrain into the network parallel electrical method processing system, and merge the original data of each section at the same time; the next step is conventional data decoding, outputting apparent resistivity data files and AGI inversion format data files, among which, the collected data needs to be checked before conventional data decoding, and if there are abnormal jump points in the data that do not conform to the actual situation, they need to be eliminated; Data inversion processing: Select the appropriate inversion method based on the on-site geological conditions and the quality of actual data collection to obtain the best inversion results. The AGI inversion software provides three inversion methods, including damped least squares inversion, smooth model inversion and anti-noise inversion. The main process is: initial setting of inversion parameters, selection of appropriate inversion method, setting of data noise standard, number of inversion iterations, smooth coefficient and maximum root mean square error; opening the AGI inversion format data file and performing joint inversion to obtain the electrical data profile of the complete underwater geological body on the entire survey line. After the inversion is completed, export the inversion resistivity data file in dat format; Data result mapping: The apparent resistivity data and the inversion resistivity data exported by the AGI inversion software are processed by the Surfer mapping software, including: opening the data in dat format in the Surfer software, gridding the data, selecting the gridding method, the grid division size and filtering the basic processing flow of abnormal data, and selecting the filter to filter the data and perform whitening processing according to actual needs. Through the above processing flow, the underwater geological electrical result map with terrain is finally obtained; (6) Analysis of underwater geological electrical properties According to the actual purpose of underwater detection and the detection results, and combined with the existing on-site geological data, the resistivity and distribution characteristics of different areas in the electrical result map are interpreted, and the underwater geological information is comprehensively analyzed and judged.