An in-situ seabed bottom material detecting device and method

Abstract

The application belongs to the technical field of ocean exploration, and specifically discloses a seabed bottom type in-situ detection device and method. The device comprises an upper computer, a transmitter and a receiver. At the transmitter end, the application modulates selected initial identification information symbols into a low-frequency carrier frequency band in a multi-band linear frequency modulation manner to generate a low-frequency modulated wave, and then modulates the low-frequency modulated wave into a high-frequency carrier in an amplitude modulation manner to form a narrow underwater acoustic beam. At the receiver end, because different types of seabed have different self-demodulation capabilities and underwater sound dissipation characteristics at different bit positions of the identification information symbols, T-BOK demodulation is realized through low-frequency echo reception to obtain a three-state identification code, and the delay information of each bit of the three-state identification code is recorded. Through the three-state identification code demodulated by the low-frequency echo, the delay information of each bit of the three-state identification code, and a three-state identification code codebook generated in advance, the seabed bottom type and distribution characteristic parameters are obtained.

Description

Technical Field

[0001] This invention belongs to the field of marine exploration technology, and specifically relates to an in-situ detection device and method for seabed sediment. Background Technology

[0002] Currently, the three main methods for in-situ detection of seabed sediment are acoustic, optical, and magnetic detection.

[0003] Optical detection often employs airborne lidar for depth measurement, utilizing dual-frequency lasers (blue-green light + near-infrared) to penetrate water and accurately measure water depth and seabed morphology. Magnetic detection, on the other hand, uses magnetic anomalies to identify ferromagnetic objects. However, optical and magnetic detection are easily limited by strict application scenarios and cannot meet the needs of in-situ seabed sediment detection in general scenarios.

[0004] Acoustic detection uses shallow seismic profilers or sonar to generate seabed topographic images based on differences in sound wave echoes, and then relies on these images to distinguish seabed types. However, this method has several drawbacks when used for in-situ seabed exploration, including high computational demands for data analysis, lack of intuitive information acquisition, limitation to identifying only shallow seabed types, high detection costs, and inaccurate identification of geological properties. Summary of the Invention

[0005] The purpose of this invention is to propose an in-situ seabed sediment detection device. This device utilizes the nonlinear underwater acoustic transmission characteristics of the seabed sediment, transmits a high-frequency modulated wave detection signal, and uses a low-frequency echo receiving unit to receive the low-frequency signal generated by the self-demodulation of the seabed sediment. Based on the information such as the three-state identification code in the low-frequency signal, and in conjunction with the three-state identification code book, the device identifies the type of seabed sediment and the distribution of various media, thereby effectively realizing in-situ seabed sediment detection.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A seabed sediment in-situ detection device includes a host computer, a transmitter, and a receiver;

[0008] The transmitter consists of a transmitter controller and a transmitter array;

[0009] The transmission controller is used to select the initial identification information code, the low-frequency carrier band and the high-frequency underwater acoustic carrier frequency, and to calculate the initial phase of the high-frequency carrier of each transmission unit in the transmission array corresponding to the in-situ detection point of the seabed sediment to be detected.

[0010] The transmitting array consists of multiple transmitting units, each of which comprises a modulator, a power amplifier, and a transducer;

[0011] The modulator generates a modulated transmission signal using a direct digital frequency synthesizer (DDS) based on the parameters of the transmit controller.

[0012] The DDS processing procedure is as follows: First, the initial identification information code is modulated onto the low-frequency carrier band using multi-band linear frequency modulation to generate a low-frequency modulated wave; then, the low-frequency modulated wave is modulated onto the high-frequency carrier using amplitude modulation.

[0013] The power amplifier amplifies the signal generated by the DDS and couples it to the transducer for transmission into the water medium;

[0014] The high-frequency carrier waves emitted by the transducers of each transmitting unit form underwater acoustic beams that are directed at predetermined in-situ detection points on the seabed.

[0015] The receiver consists of a high-frequency echo receiving unit, a low-frequency echo receiving unit, and a seabed sediment identification unit;

[0016] The high-frequency echo receiving unit is used to acquire the distance and deflection angle information of the water-substrate interface;

[0017] The low-frequency echo receiving unit is used to collect low-frequency underwater acoustic signals that have been automatically demodulated by the seabed sediment layer. It performs demodulation processing through T-BOK modulation to demodulate the three-state identifier code and records the delay information of each bit of the three-state identifier code.

[0018] The seabed sediment identification unit is used to obtain the seabed sediment type and distribution characteristic parameters by using the tri-state identification code demodulated by the low-frequency echo receiving unit, the delay information of each bit of the tri-state identification code, and the pre-generated tri-state identification code book.

[0019] Furthermore, based on the aforementioned in-situ seabed sediment detection device, this invention also proposes a corresponding in-situ seabed sediment detection method. This method is implemented based on the aforementioned in-situ seabed sediment detection device and adopts the following technical solution:

[0020] A method for in-situ detection of seabed sediment includes the following steps:

[0021] Step 1. Pre-generate and calibrate the three-state identification codebook; the three-state identification codebook is a combination of multiple codewords, and each codeword is assigned a corresponding seabed sediment property parameter vector;

[0022] Step 2. Based on the in-situ detection scenario of the seabed sediment, the transmitter controller selects different initial identification information symbols, low-frequency carrier frequency bands, and high-frequency underwater acoustic carrier frequencies;

[0023] Step 3. The DDS modulates the initial identification information symbols onto the designed low-frequency carrier band using multi-band linear frequency modulation; then it modulates the low-frequency modulated wave onto the high-frequency underwater acoustic carrier using amplitude modulation to obtain the high-frequency modulated wave.

[0024] Step 4. Select the distance and deflection angle of the in-situ detection point on the seabed sediment, calculate the initial phase of the high-frequency carrier of each transmitting unit in the transmitting array, and couple the high-frequency modulated wave to the corresponding transmitting unit after adjusting the phase.

[0025] Step 5. The high-frequency modulated wave, which is given an initial phase, is amplified by the power amplifier of each transmitting unit and then emitted by the transducer of that transmitting unit, thereby forming an underwater acoustic beam pointing to the predetermined in-situ detection point on the seabed.

[0026] Step 6. The high-frequency echo receiving unit receives the high-frequency echo signal, performs filtering and amplification processing, and then determines the actual interface distance and deflection angle between the seabed and the seabed at the in-situ detection point of the seabed sediment by the echo delay.

[0027] Step 7. The low-frequency echo receiving unit receives the low-frequency modulated echo signal, performs filtering and amplification, and then performs T-BOK demodulation processing to generate a three-state identification code containing seabed sediment information, and records the delay information of each bit of the three-state identification code.

[0028] Step 8. Find the nearest codeword in the three-state identification codebook for the bottom sediment three-state identification code, analyze the seabed sediment property parameter vectors corresponding to the codeword and the codewords next to it, and combine the delay parameters of each bit of the codeword to obtain the bottom sediment identification result.

[0029] The present invention has the following advantages:

[0030] As described above, this invention relates to an in-situ detection device and method for seabed sediment. This device utilizes the nonlinear underwater acoustic transmission characteristics caused by the inhomogeneity of the seabed sediment, and designs a high-frequency carrier, a low-frequency carrier, and initial detection identification information code elements. It employs high-frequency underwater acoustic transmission, low-frequency echo reception, and demodulation of the identification information code elements to achieve in-situ detection of the seabed sediment. This invention fully utilizes the self-demodulation process of the seabed sediment on modulated waves to obtain low-frequency modulated waves. The low-frequency modulated waves are then demodulated using Ternary Binary Orthogonal Keying (T-BOK), thereby assigning different T-state identification codes to seabed sediments of different properties. By querying and analyzing the calibrated T-state identification codebook and the seabed sediment property parameters corresponding to each codeword in the codebook, the properties of the seabed sediment are analyzed and calculated, thus achieving in-situ detection and identification of the seabed sediment. This invention reduces the transducer size and achieves a narrower transmission beam through high-frequency transmission, which is beneficial for concentrating the underwater acoustic energy at the detection point. By receiving the low-frequency underwater acoustic signal after self-demodulation by the seabed sediment, it is possible to directly acquire encoded information using different characteristic parameters of the seabed sediment, reducing the computational load for identifying seabed sediment type and distribution characteristics, and improving the accuracy of in-situ seabed sediment detection. This invention cleverly utilizes the self-demodulation of high-frequency modulated signals by the seabed sediment. The in-situ seabed sediment detection device is simple and easy to implement, and this invention has better detection effect and the potential to reduce costs compared to other detection methods. Attached Figure Description

[0031] Figure 1 This is a structural block diagram of the seabed sediment in-situ detection device in Embodiment 1 of the present invention;

[0032] Figure 2 This is a schematic diagram of the frequency band allocation of each bit of the symbol in the multi-band linear frequency modulation method of Embodiment 1 of the present invention;

[0033] Figure 3 This is a flowchart of the in-situ detection method for seabed sediment in Embodiment 2 of the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0035] Example 1

[0036] This embodiment 1 describes an in-situ seabed sediment detection device to achieve in-situ detection of seabed sediment, such as... Figure 1 As shown, the seabed sediment in-situ detection device in this embodiment includes a host computer, a transmitter, and a receiver.

[0037] The host computer is used to control the transmitter's signal transmission time, set the detection area, and configure the signal parameters. It can also store the seabed sediment identification results from the receiver.

[0038] Different sea areas have different water depths and seabed sediment distribution characteristics. The host computer needs to transmit the detected sea area information, such as latitude and longitude, to the transmitter so that the transmitter controller can determine the attitude angle of the transmission array surface, select the initial identification information code, low-frequency carrier frequency band and high-frequency underwater acoustic carrier frequency based on this information, and calculate the initial phase of the high-frequency carrier of each transmission unit in the transmission array corresponding to the in-situ detection point of the seabed sediment to be detected.

[0039] In actual detection, the detection signal parameters refer to the initial identification information symbols, low-frequency carrier frequency band, and high-frequency underwater acoustic carrier frequency recommended to the transmitter by the host computer based on the characteristics of the sea area and past experience.

[0040] However, after receiving the initial identification information symbols, low-frequency carrier frequency band, and high-frequency underwater acoustic carrier frequency, the transmitter controller still needs to make adaptive adjustments based on the attitude data of the transmitter array and receiver array to achieve the best detection effect.

[0041] The transmitter consists of a transmitter controller and a transmitter array.

[0042] The transmission controller is used to select the initial identification information code, the low-frequency carrier band, and the high-frequency underwater acoustic carrier frequency, and to calculate the initial phase of the high-frequency carrier of each transmission unit in the transmission array corresponding to the in-situ detection point of the seabed sediment to be detected.

[0043] In this embodiment, the transmission controller can select different initial identification information symbols based on prior knowledge of the sea area to be probed. If high precision is required, more symbol bits are selected; if lower precision is required, fewer symbol bits are selected. In this embodiment, the selected initial identification information symbols are, for example, 0xAAAAH or 0x5555H.

[0044] The low-frequency carrier band is from 200Hz to 2KHz, and the high-frequency underwater acoustic carrier frequency is 28KHz.

[0045] The calculation of the initial phase of the high-frequency carrier of each transmitting element in the transmitting array is relatively conventional and is the same as the calculation method of the transmitting phase of each antenna element of the existing phased array radar and the carrier phase of each antenna element of the mobile communication antenna array.

[0046] In practice, seabed sediment detection devices typically use area arrays for their transmitting arrays, mainly because area arrays are simpler and the beam direction can be flexibly controlled. In this embodiment, the transmitting array consists of multiple transmitting units.

[0047] The entire transmitting array consists of transmitting units that are uniformly and symmetrically distributed in a planar manner.

[0048] like Figure 1 The diagram shows transmitting units 1 to n, where n is a natural number, and their transmitted signals are directional. All transmitting units have identical structures and are arranged according to a specific pattern.

[0049] For example, in this embodiment, the transmitting array consists of 6 transmitting units arranged in a regular hexagon.

[0050] Each transmitting element is located at a vertex of a regular hexagon. This is done to create a regular beam shape with the main lobe perpendicular to the transmitting array, making it easier to calculate the transmission parameters and control the beam direction.

[0051] The side length of a regular hexagon is, for example, 20 centimeters, and its value can be adjusted according to power and beamwidth requirements.

[0052] Of course, the transmitting array can also consist of 5 transmitting units, with each unit located at a vertex of a regular pentagon. Alternatively, the transmitting array can use 7 transmitting units. Of course, other numbers of transmitting units can also be used.

[0053] Taking one of the transmitting units as an example, each transmitting unit consists of a modulator, a power amplifier, and a transducer.

[0054] The modulator generates a modulated transmission signal using a Direct Digital Synthesizer (DDS) based on the parameters of the transmit controller; the DDS processing procedure is as follows:

[0055] Firstly, as shown in Figure 2 The method shown for allocating each bit of the symbol in the frequency band modulates the initial identification information symbol to the low-frequency carrier band using a multi-band linear frequency modulation method to generate a low-frequency modulated wave.

[0056] in Figure 2 middle and These represent the lower and upper limits of the low-frequency carrier band, respectively. , , , , , , … , These represent the cutoff frequencies of the m sub-bands divided into the low-frequency carrier band.

[0057] like Figure 2As shown, multi-band linear frequency modulation is more conventional. In multi-band linear frequency modulation, the 0 and 1 states of the bit are modulated by up-modulation and down-modulation in the corresponding sub-bands of the low-frequency carrier band, respectively.

[0058] The low-frequency modulated wave is then modulated onto a high-frequency carrier wave using amplitude modulation to obtain a high-frequency modulated wave. Next, the power amplifier amplifies the signal generated by the DDS, i.e., the high-frequency modulated wave, and couples it to a transducer for transmission into the water medium.

[0059] Each transmitting unit's transducer emits a high-frequency carrier wave, forming a narrow underwater acoustic beam that is directed towards a predetermined in-situ detection point on the seabed. High-frequency transmission reduces the transducer size and achieves a narrower transmission beam, which helps to concentrate the underwater acoustic energy at the detection point.

[0060] The receiver consists of a high-frequency echo receiving unit, a low-frequency echo receiving unit, and a seabed sediment identification unit.

[0061] The high-frequency echo receiving unit is used to receive and process reflected waves generated by the water-seabed interface to obtain the distance and deflection angle information of the water-seabed interface.

[0062] The low-frequency echo receiving unit receives and processes the echo generated by the self-demodulation of the seabed sediment, performs demodulation processing through T-BOK modulation, demodulates the three-state identifier code, and records the delay information of each bit of the three-state identifier code.

[0063] Specifically, the high-frequency echo receiving unit includes a high-frequency hydrophone and a signal processor.

[0064] The high-frequency hydrophone receives reflected waves from the interface between the water and the seabed, filters and amplifies them, and then couples them to the signal processor. In the signal processor, high-frequency signal processing is performed to obtain the distance and deflection angle information of the water-seabed interface.

[0065] It should be noted that high-frequency signal processing is relatively conventional. For example, GPS, BeiDou, underwater acoustic positioning, and the elimination of multipath effects in mobile communication all use the same carrier signal processing method as this invention to obtain distance and deflection angle.

[0066] The distance and angle information of the water-substrate interface acquired by the high-frequency hydrophone is mainly used to determine the relative relationship between the spatial position of the substrate and the spatial position of the receiver, and is not used to identify the properties and distribution characteristics of the substrate medium.

[0067] However, the information obtained by the high-frequency hydrophone is necessary for the detection device and will be recorded in the detection database. Using this information in combination with the latitude and longitude of the detection device and the attitude of the receiver, imaging processing can be performed. This is not the point of invention and will not be elaborated further.

[0068] In addition, the information obtained is also necessary for determining the distribution characteristics of various seabed sediments in a certain sea area.

[0069] The low-frequency echo receiver unit includes a low-frequency hydrophone and a T-BOK demodulator.

[0070] The low-frequency hydrophone collects the low-frequency underwater acoustic signal that has been automatically demodulated by the seabed sediment layer, and then filters and amplifies it. The demodulator performs demodulation processing according to the T-BOK modulation method, demodulates the three-state identifier code, and records the delay information of each bit of the three-state identifier code.

[0071] The T-BOK demodulation process is relatively conventional. T-BOK demodulation maps up-modulation, down-modulation, and no signal to three states: 0, 1, and N, respectively, based on the reception status of the linear frequency modulation signal sub-band.

[0072] The seabed sediment identification unit is used to obtain the seabed sediment type and distribution characteristic parameters by using the tri-state identification code demodulated by the low-frequency echo receiving unit, the delay information of each bit of the tri-state identification code, and the pre-generated tri-state identification code book.

[0073] Distribution characteristic parameters refer to parameters such as the properties of various media layers, the vertical order of each media layer, and the thickness of each media layer.

[0074] The seabed sediment identification unit is a computational unit with seabed sediment identification capabilities, used to identify seabed sediment types. In this embodiment, the seabed sediment identification unit identifies the sediment type through a three-state identifier, the general process of which is as follows:

[0075] First, find the nearest codeword in the three-state identifier codebook for the seabed sediment three-state identifier code. Then, analyze the seabed sediment property parameter vectors corresponding to the codeword and its neighboring codewords, and combine the delay parameters of each bit of the codeword to obtain the seabed sediment identification result.

[0076] At the receiver end, since different types of seabed sediments have different self-demodulation capabilities and underwater acoustic dissipation characteristics at different bit positions of the identification information code, this invention achieves T-BOK demodulation through low-frequency echo reception to obtain a tri-state identification code, and records the delay information of each bit of the tri-state identification code. Through the tri-state identification code, the delay information of each bit of the tri-state identification code, and the pre-generated and calibrated tri-state identification code book, the seabed sediment type and distribution characteristic parameters can be obtained.

[0077] The following is an explanation of the seabed sediment: water, sand, gravel, stone, mud, and mixtures of them in different proportions are all media for the detection device. The seabed sediment is composed of these media, and the sediment type is classified according to the distribution characteristics of various media in the seabed sediment (the distribution order of different media layers, the properties of each media layer, and the thickness).

[0078] Because the types of seabed sediments are infinitely numerous and cannot be precisely described, different countries and industries have developed different standards. These standards specify the proportion range of "water-mud-sand-gravel-stone" for different media types to distinguish between different seabed sediments. Since there are currently no corresponding international or national standards, in-situ seabed sediment detection devices often provide distribution characteristic parameters of each medium in the sediment to adapt to the standard specifications of different application fields.

[0079] Example 2

[0080] This embodiment 2 describes an in-situ seabed sediment detection method, which is based on the same inventive concept as the in-situ seabed sediment detection device in embodiment 1 above. For example... Figure 3 As shown, the in-situ seabed sediment detection method in this embodiment is based on the aforementioned in-situ seabed sediment detection device, and specifically includes the following steps:

[0081] Step 1. Pre-generate and calibrate the tri-state identification codebook; the tri-state identification codebook is a combination of multiple codewords, and each codeword is assigned a corresponding vector of seabed sediment property parameters, that is, a vector representation of seabed sediment property parameters.

[0082] Seabed sediment types are generally described by a property parameter vector consisting of "the distribution order of multiple media layers, the properties of each media layer, and the thickness of each media layer". The composition of the seabed sediment property parameter vector is: layer 1 media property + layer 1 media thickness + layer 2 media property + layer 2 media thickness + ... + layer n media property + layer n media thickness.

[0083] The multi-layered media contains multiple single-layer media such as sediment, coarse sand, and pebbles. The sediment has a cement ratio of 3:5 and is 25 cm thick; the coarse sand has a water-to-sand ratio of 1:2 and is 12 cm thick; and the pebbles have a water:sand:pebble ratio of 1:2:3 and are 10 cm thick.

[0084] In the tri-state identification codebook, a codeword is a tri-state identification code plus a vector of seabed sediment property parameters.

[0085] One of the three-state identifier codes is composed of multiple three-state bits. The seabed sediment property parameter vector is a combination of the properties and thickness information parameters of each medium layer of the seabed sediment corresponding to the three-state identifier code, which were measured in the previous stage.

[0086] In the database, each codeword occupies one record in the database table.

[0087] The three-state identifier, layer 1 medium property, layer 1 medium thickness, layer 2 medium property, layer 2 medium thickness, ..., layer n medium property, layer n medium thickness are each a field of this record.

[0088] In this way, a three-state identifier is associated with a vector of seabed sediment property parameters.

[0089] The tri-state identifier codebook is actually a table, often stored in a database. For the purposes of this invention, if the tri-state identifier is n bits, the table (codebook) has 3... n Each codeword corresponds to a distribution characteristic parameter of a type of seabed sediment.

[0090] These distribution characteristic parameters are usually stored in a database in the form of a vector of seabed sediment property parameters.

[0091] The tri-state identification codebook needs to be calibrated before use. The calibration method is as follows:

[0092] Experimental scenarios are constructed in the laboratory or test site using different seabed sediment distributions. Tri-state identification codes are obtained by measuring with instruments. The tri-state identification codes of different sediment distributions are combined with their corresponding sediment distribution characteristic parameters to form codewords.

[0093] Change the substrate type and repeat the above operations until a complete tri-state identification codebook is generated, thus completing the calibration process.

[0094] Step 2. Based on the in-situ detection scenario of the seabed sediment, the transmitter controller selects different initial identification information symbols, low-frequency carrier frequency bands, and high-frequency underwater acoustic carrier frequencies using prior knowledge of the sea area.

[0095] Step 3. The DDS modulates the initial identification information symbols onto the designed low-frequency carrier band using multi-band linear frequency modulation; then it modulates the low-frequency modulated wave onto the high-frequency underwater acoustic carrier using amplitude modulation to obtain the high-frequency modulated wave.

[0096] Step 4. Select the distance and deflection angle of the in-situ detection point on the seabed sediment, calculate the initial phase of the high-frequency carrier of each transmitting unit in the transmitting array, and couple the high-frequency modulated wave to the corresponding transmitting unit after adjusting the phase.

[0097] Step 5. The high-frequency modulated wave, which is given an initial phase, is amplified by the power amplifier of each transmitting unit and then emitted by the transducer of that transmitting unit, thereby forming a narrow underwater acoustic beam pointing to the predetermined in-situ detection point on the seabed.

[0098] In this embodiment, the low-frequency modulated wave is modulated onto the low-frequency carrier band by the initial identification information code element using multi-band linear frequency modulation, and the high-frequency modulated wave is modulated onto the selected high-frequency carrier by the low-frequency modulated wave using amplitude modulation.

[0099] Step 6. The high-frequency echo receiving unit receives the high-frequency echo signal, performs filtering and amplification processing, and then determines the actual interface distance and deflection angle between the seabed and the seabed at the in-situ detection point of the seabed sediment by the echo delay.

[0100] Only by using distance and deflection information can the relative relationship between the spatial position of the substrate and the spatial position of the receiver be determined.

[0101] Wherein, the actual interface distance between the seabed and the seabed = echo delay × wave speed / 2.

[0102] In the section on seabed sediment identification below, the distance and angle information between the water and the seabed interface were not used. The distance and angle information between the water and the seabed interface is only used to determine the spatial relative position of the seabed sediment, and is not used to identify the seabed sediment.

[0103] Step 7. The low-frequency echo receiving unit receives the low-frequency modulated echo signal, performs filtering and amplification, and then performs T-BOK demodulation processing to generate a three-state identification code containing seabed sediment information, and records the delay information of each bit of the three-state identification code.

[0104] Step 8. Find the nearest codeword in the three-state identification codebook for the bottom sediment three-state identification code, analyze the seabed sediment property parameter vectors corresponding to the codeword and the codewords next to it, and combine the delay parameters of each bit of the codeword to obtain the bottom sediment identification result.

[0105] This invention, for example, can use vector distance calculation to compare and determine the closest codeword in the codebook. The seabed sediment property parameters are arranged in ascending order of delay parameter, corresponding to seabed depths from shallow to deep.

[0106] In a specific example, taking the initial identification information code element as 0x5555H, the modulation and decoding process is briefly described as follows:

[0107] Step I. The binary representation of 0x5555H is 0101010101010101. Using a multi-band linear frequency modulation method, the initial identification information symbols are modulated onto 16 sub-bands between 200Hz and 2kHz, i.e.:

[0108] f1=200Hz, f2=310Hz, f3=420Hz, f4=530Hz, f5=640Hz, f6=750Hz...f16=1850Hz, f17=2KHz.

[0109] The sub-frequency bands of the modulated low-frequency wave, in chronological order, are as follows:

[0110] f1-f2,f9-f8,f2-f3,f10-f9,f3-f4,f11-f10...f7-f6,f17-f16.

[0111] Within each sub-band, linear frequency modulation is used, that is, "0" is modulated upwards and "1" is modulated downwards.

[0112] Step II. Modulate the low-frequency modulated wave onto a 28kHz high-frequency carrier using amplitude modulation and transmit it through the transmitting array.

[0113] Step III. After the detection signal reaches the seabed sediment, it is demodulated into a low-frequency modulated wave. Due to the different seabed sediments, the returned low-frequency modulated waves vary greatly. After T-BOK demodulation, the three-state identifier and the delay information of each bit of the three-state identifier are obtained.

[0114] For example, if the medium layer of a certain seabed substrate consists of coarse sand, gravel, and reef from top to bottom, the resulting three-state identifier is 0W0W01010101W1W1, where W is the third state, which is neither 0 nor 1, meaning that the received signal is not the expected one.

[0115] The delays for each bit are 325ms, 326.2ms, 325.1ms, 326.1ms, ..., 325.8ms, 328.3ms.

[0116] For example, if the media layer of a certain seabed substrate consists of mud, fine sand, gravel, and reef from top to bottom, the resulting three-state identifier is 01W1W1010W01010W, where W is the third state, which is neither 0 nor 1, meaning that the received signal is not the expected one.

[0117] The delays for each bit are 506ms, 496.2ms, 505.1ms, 498.1ms, ..., 495.8ms, 499.3ms.

[0118] Step IV. By using the three-state identifier and the delay information of each bit, combined with the three-state identifier codebook, identify each layer of the seabed substrate, determine the properties and thickness of each layer, and the distribution order of each layer from top to bottom.

[0119] Of course, the above description is only a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. It should be noted that any equivalent substitutions or obvious modifications made by those skilled in the art under the guidance of this specification fall within the scope of this specification and should be protected by the present invention.

Claims

1. A seabed sediment in-situ detection device, characterized in that, Includes host computer, transmitter, and receiver; The transmitter consists of a transmitter controller and a transmitter array; The transmission controller is used to select the initial identification information code, the low-frequency carrier band and the high-frequency underwater acoustic carrier frequency, and to calculate the initial phase of the high-frequency carrier of each transmission unit in the transmission array corresponding to the in-situ detection point of the seabed sediment to be detected. The transmitting array consists of multiple transmitting units, each of which comprises a modulator, a power amplifier, and a transducer; The modulator generates a modulated transmission signal using a direct digital frequency synthesizer (DDS) based on the parameters of the transmit controller. The DDS processing procedure is as follows: First, the initial identification information code is modulated onto the low-frequency carrier band using multi-band linear frequency modulation to generate a low-frequency modulated wave; then, the low-frequency modulated wave is modulated onto the high-frequency carrier using amplitude modulation. The power amplifier amplifies the signal generated by the DDS and couples it to the transducer for transmission into the water medium; The high-frequency carrier waves emitted by the transducers of each transmitting unit form underwater acoustic beams that are directed at predetermined in-situ detection points on the seabed. The receiver consists of a high-frequency echo receiving unit, a low-frequency echo receiving unit, and a seabed sediment identification unit; The high-frequency echo receiving unit is used to acquire the distance and deflection angle information of the water-substrate interface; The low-frequency echo receiving unit is used to collect low-frequency underwater acoustic signals that have been automatically demodulated by the seabed sediment layer. It performs demodulation processing through T-BOK modulation to demodulate the three-state identifier code and records the delay information of each bit of the three-state identifier code. The seabed sediment identification unit is used to obtain the seabed sediment type and distribution characteristic parameters by using the tri-state identification code demodulated by the low-frequency echo receiving unit, the delay information of each bit of the tri-state identification code, and the pre-generated tri-state identification code book.

2. The in-situ seabed sediment detection device according to claim 1, characterized in that, The high-frequency echo receiving unit includes a high-frequency hydrophone and a signal processor; The high-frequency hydrophone receives reflected waves from the interface between the water and the seabed, filters and amplifies them, and then couples them to the signal processor. In the signal processor, high-frequency signal processing is performed to obtain the distance and deflection angle information of the water-seabed interface. The low-frequency echo receiving unit includes a low-frequency hydrophone and a T-BOK demodulator; The low-frequency hydrophone collects the low-frequency underwater acoustic signal that has been automatically demodulated by the seabed sediment layer, and then filters and amplifies it. The demodulator performs demodulation processing according to the T-BOK modulation method, demodulates the three-state identifier code, and records the delay information of each bit of the three-state identifier code.

3. The in-situ seabed sediment detection device according to claim 1, characterized in that, The seabed sediment identification unit is a computing unit used for seabed sediment identification.

4. The in-situ seabed sediment detection device according to claim 1, characterized in that, The host computer is used to control the transmission time of the transmitter's detection signal, set the detection area and detection signal parameters, and store the seabed sediment identification results of the receiver.

5. The in-situ seabed sediment detection device according to claim 1, characterized in that, The transmitting array consists of multiple transmitting units, all of which are uniformly and symmetrically distributed in a planar manner.

6. The in-situ seabed sediment detection device according to claim 1, characterized in that, The tri-state identifier codebook is a combination of multiple codewords, and each codeword is assigned a corresponding vector of seabed sediment property parameters.

7. The in-situ seabed sediment detection device according to claim 1, characterized in that, The initial identification information code element is 0XAAAAH or 0X5555H; The low-frequency carrier band is from 200Hz to 2KHz, and the high-frequency underwater acoustic carrier frequency is 28KHz.

8. The in-situ seabed sediment detection device according to claim 1, characterized in that, The 0 and 1 states of the bit in the multi-band linear frequency modulation method are modulated in the corresponding sub-bands of the low-frequency carrier band using up-modulation and down-modulation methods, respectively.

9. The in-situ seabed sediment detection device according to claim 1, characterized in that, The T-BOK demodulation process maps up-modulation, down-modulation, and no signal to three states: 0, 1, and N, respectively, based on the reception status of the linear frequency modulation signal sub-band.

10. A method for in-situ detection of seabed sediment, based on the in-situ detection device for seabed sediment as described in any one of claims 1 to 9, characterized in that, The in-situ detection method for seabed sediment includes the following steps: Step 1. Pre-generate and calibrate the three-state identification codebook; the three-state identification codebook is a combination of multiple codewords, and each codeword is assigned a corresponding seabed sediment property parameter vector; Step 2. Based on the in-situ detection scenario of the seabed sediment, the transmitter controller selects different initial identification information symbols, low-frequency carrier frequency bands, and high-frequency underwater acoustic carrier frequencies; Step 3. The DDS modulates the initial identification information symbols onto the designed low-frequency carrier band using multi-band linear frequency modulation; then it modulates the low-frequency modulated wave onto the high-frequency underwater acoustic carrier using amplitude modulation to obtain the high-frequency modulated wave. Step 4. Select the distance and deflection angle of the in-situ detection point on the seabed sediment, calculate the initial phase of the high-frequency carrier of each transmitting unit in the transmitting array, and couple the high-frequency modulated wave to the corresponding transmitting unit after adjusting the phase. Step 5. The high-frequency modulated wave, which is given an initial phase, is amplified by the power amplifier of each transmitting unit and then emitted by the transducer of that transmitting unit, thereby forming an underwater acoustic beam pointing to the predetermined in-situ detection point on the seabed. Step 6. The high-frequency echo receiving unit receives the high-frequency echo signal, performs filtering and amplification processing, and then determines the actual interface distance and deflection angle between the seabed and the seabed at the in-situ detection point of the seabed sediment by the echo delay. Step 7. The low-frequency echo receiving unit receives the low-frequency modulated echo signal, filters and amplifies it, and then performs T-BOK demodulation processing to generate a three-state identification code for the seabed sediment that contains seabed sediment information, and records the delay information of each bit of the three-state identification code. Step 8. Find the nearest codeword in the three-state identification codebook for the bottom sediment three-state identification code, analyze the seabed sediment property parameter vectors corresponding to the codeword and the codewords next to it, and combine the delay parameters of each bit of the codeword to obtain the bottom sediment identification result.

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