Shallow seabed geoacoustic parameter inversion method, system, equipment and medium based on very low frequency water-ground modal interferometry

Abstract

The present invention proposes a shallow seabed geoacoustic parameter inversion method, system, equipment and medium based on very low frequency water-ground modal interference. The present invention considers very low frequency sound propagation in a layered shallow sea environment, and part of the energy is coupled into the seabed to capture the geoacoustic mode propagation of the sediment layer. The water acoustic mode group velocity is negatively dispersed and the geoacoustic mode is positively dispersed. Therefore, the interference structure of the two is no longer in the form of stripes, but changes nonlinearly with frequency. This special interference structure is related to the modal propagation and dispersion characteristics in the sediment layer, and the dispersion characteristics are related to the acoustic parameters of the water body and the seabed. It is a new method for inverting environmental parameters with better inversion effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydroacoustic physics, and in particular relates to a shallow sea bottom geoacoustic parameter inversion method, system, equipment and medium based on very low frequency water-ground modal interference. Background Art

[0002] Since Chuprov proposed the concept of waveguide invariants in 1982, the sound intensity fringes observed in the range-frequency domain have been widely studied. Existing studies have shown that β≈1 in a typical shallow-water waveguide environment, and this quantity is quite stable relative to small perturbations in the sound velocity profile, which makes it widely used in passive ranging of broadband sound sources. In addition, the value of β can also describe the modal dispersion in the waveguide, which has an intrinsic relationship with the properties of the waveguide, making it also widely used in geoacoustic parameter inversion and array signal processing (modal filtering, noise suppression, etc.).

[0003] At present, most of the research conducted by domestic and foreign scholars believes that the waveguide invariant is a fixed scalar. The few studies on the change of waveguide invariant are all the influence of hydrological changes. In the case of non-uniform sound velocity profiles such as negative jump layers, the interference fringe structure of the sound field is complex, and the fringe slope and the corresponding waveguide invariant value have a certain distribution range, which is difficult to describe with a fixed constant.

[0004] However, there is no research on the changes of waveguide invariants caused by seafloor acoustic parameters. When considering the propagation of very low frequency sound in a stratified shallow sea environment, part of the energy is coupled into the seafloor to propagate as the geoacoustic mode captured by the sediment layer. The group velocity of the hydroacoustic mode is negatively dispersed while the geoacoustic mode is positively dispersed. Therefore, the interference structure of the two is no longer in the form of stripes, but changes nonlinearly with frequency. This special interference structure is sensitive to changes in seafloor parameters and can be used for the inversion of seafloor geoacoustic parameters. Summary of the invention

[0005] In order to solve the problems in the prior art, the present invention proposes a shallow sea seabed geoacoustic parameter inversion method, system, equipment and medium based on very low frequency water-ground modal interference to obtain effective seabed acoustic parameters in a layered shallow sea environment.

[0006] The present invention is realized by the following technical scheme. The present invention proposes a shallow seabed geoacoustic parameter inversion method based on very low frequency water-ground modal interference, and the method comprises the following steps:

[0007] Step 1: Multiple hydrophones or OBS are deployed in the water, the ship sails, and then throws explosion sound sources or launches very low frequency airgun sound sources into the sea at fixed time intervals. After traversing the surveyed sea area, it returns and retrieves the receiving equipment to obtain sound pressure data in the time-distance domain;

[0008] Step 2: Perform preliminary processing and analysis on the sound pressure data in the time-distance domain. First, obtain the prior information of the ocean environment from the experimental data, determine the base sound velocity range using the propagation velocity of the base lateral wave, and then use the frequency-wavenumber domain characteristics to perform modal filtering to retain only the first-order water acoustic mode and the first-order ground acoustic mode with strong energy. Perform Fourier transform on the retained data to obtain the water-ground mode sound intensity interference structure in the distance-frequency domain.

[0009] Step 3: Extract the water-ground modal interference fringe curve in the distance-frequency domain of the experimental data, and calculate the distribution of the waveguide invariant with frequency using the following formula:

[0010]

[0011] Where: β represents the waveguide invariant, r0 represents the center distance between the sound source and the receiving point, f0 represents the center frequency, f represents the frequency, and r represents the distance;

[0012] Step 4: Theoretically calculate the variation of intermodal interference fringes with frequency. The specific calculation method is as follows:

[0013] On the distance-frequency plane, for a specific interference fringe, the sound intensity at each point on it is a constant, then:

[0014]

[0015] Where I represents the sound intensity, ω = 2πf is the angular frequency;

[0016] From the sound intensity expression we get:

[0017]

[0018]

[0019] Among them, m and n represent the order of the simple normal wave, A m and A n is the simple normal wave modal intensity, * represents the complex conjugate, Δk mn is the wave number difference between modes;

[0020] Substitute equation (3) and equation (4) into equation (2):

[0021]

[0022] Then we have:

[0023]

[0024] The theoretical expression of the fringe slope, i.e. the waveguide invariant of the two-order modal interference structure, is obtained as follows:

[0025]

[0026] Among them, β mn represents the waveguide invariant of the mth and nth order interference; I0 is a constant, S pm , S pn are the phase slowness of the m-order and n-order modes, S gm , S gn are the group slownesses of the m-order and n-order modes respectively;

[0027] From the above formula, we can know that the theoretical value of the waveguide invariant of the two-order modal interference structure is expressed as the ratio of the phase slowness difference between the modes to the group slowness difference. The phase velocity and group velocity dispersion curves can be obtained by using the acoustic field calculation software Kraken under the simple normal wave theory, that is, the distribution of the phase velocity and group velocity of each order of simple normal wave with frequency. Substituting into formula (7), we can obtain the distribution of the theoretical value of the waveguide invariant of the two-order modal interference structure with frequency β mn (f);

[0028] Step 5: Use the waveguide invariant β of water-ground modal interference mn Distribution with frequency as objective function in, The waveguide invariant representing the two-order modal interference structure extracted from the data is distributed over frequency, The theoretical calculated value is obtained by using Bayesian inversion optimization to calculate the cumulative minimum mean square error at multiple frequencies and obtain the minimum value of the objective function. At this time, the corresponding optimal value of the optimization parameter is the seabed parameter obtained by inversion.

[0029] The present invention proposes a shallow seabed geoacoustic parameter inversion system based on very low frequency water-ground modal interference, the system comprising:

[0030] Data acquisition module: multiple hydrophones or OBS are deployed in the water, the ship sails, and then throws explosion sound sources or launches very low frequency airgun sound sources into the sea at fixed time intervals, traverses the surveyed sea area and returns, and retrieves the receiving equipment to obtain sound pressure data in the time-distance domain;

[0031] Data processing module: Preliminary processing and analysis of the sound pressure data in the time-distance domain. First, the prior information of the ocean environment is obtained from the experimental data. The propagation speed of the base side wave is used to determine the base sound speed range. Then, the frequency wavenumber domain characteristics are used to perform modal filtering to retain only the first-order water acoustic mode and the first-order ground acoustic mode with strong energy. The retained data is Fourier transformed to obtain the water-ground mode sound intensity interference structure in the distance-frequency domain.

[0032] Waveguide invariant calculation module: extract the water-ground modal interference fringe curve in the distance-frequency domain of the experimental data, and calculate the distribution of the waveguide invariant with frequency using the following formula:

[0033]

[0034] Where: β represents the waveguide invariant, r0 represents the center distance between the sound source and the receiving point, f0 represents the center frequency, f represents the frequency, and r represents the distance;

[0035] Theoretical calculation module: Theoretically calculate the change of intermodal interference fringes with frequency. The specific calculation method is as follows:

[0036] On the distance-frequency plane, for a specific interference fringe, the sound intensity at each point on it is a constant, then:

[0037]

[0038] Where I represents the sound intensity, ω = 2πf is the angular frequency;

[0039] From the sound intensity expression we get:

[0040]

[0041]

[0042] Among them, m and n represent the order of the simple normal wave, A m and A n is the simple normal wave modal intensity, * represents the complex conjugate, Δk mn is the wave number difference between modes;

[0043] Substitute equation (3) and equation (4) into equation (2):

[0044]

[0045] Then we have:

[0046]

[0047] The theoretical expression of the fringe slope, i.e. the waveguide invariant of the two-order modal interference structure, is obtained as follows:

[0048]

[0049] Among them, β mn represents the waveguide invariant of the mth and nth order interference; I0 is a constant, S pm , S pn are the phase slowness of the m-order and n-order modes, S gm , S gn are the group slownesses of the m-order and n-order modes respectively;

[0050] From the above formula, we can know that the theoretical value of the waveguide invariant of the two-order modal interference structure is expressed as the ratio of the phase slowness difference between the modes to the group slowness difference. The phase velocity and group velocity dispersion curves can be obtained by using the acoustic field calculation software Kraken under the simple normal wave theory, that is, the distribution of the phase velocity and group velocity of each order of simple normal wave with frequency. Substituting into formula (7), we can obtain the distribution of the theoretical value of the waveguide invariant of the two-order modal interference structure with frequency β mn (f);

[0051] Inversion module: The waveguide invariant β of water-ground modal interferometry will be used mn Distribution with frequency as objective function in, The waveguide invariant representing the two-order modal interference structure extracted from the data is distributed over frequency, The theoretical calculated value is obtained by using Bayesian inversion optimization to calculate the cumulative minimum mean square error at multiple frequencies and obtain the minimum value of the objective function. At this time, the corresponding optimal value of the optimization parameter is the seabed parameter obtained by inversion.

[0052] The present invention also proposes an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and is characterized in that when the processor executes the computer program, it implements the steps of the shallow seabed geoacoustic parameter inversion method based on very low frequency water-ground modal interference.

[0053] The present invention also proposes a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the shallow seabed geoacoustic parameter inversion method based on very low frequency water-ground modal interference.

[0054] The technical effect of the present invention is that in the shallow seabed geoacoustic parameter inversion method based on very low frequency water-ground mode interference fringes proposed by the present invention, the interference structure used is the interference effect of the water acoustic mode and the geoacoustic mode in the sediment layer. Different from the light and dark stripe form used in the past, the slope of the interference structure in the present invention changes with frequency. The cause of this interference structure is studied by returning to the basic theory. The theoretical analysis results show that when considering the very low frequency sound propagation in a stratified shallow sea environment, part of the energy is coupled into the seabed to capture the geoacoustic mode propagation in the sediment layer. The water acoustic mode group velocity is negatively dispersed and the geoacoustic mode is positively dispersed. Therefore, the interference structure of the two is no longer in the form of stripes, but changes nonlinearly with frequency. This special interference structure is related to the mode propagation and dispersion characteristics in the sediment layer, and the dispersion characteristics are related to the acoustic parameters of the water body and the seabed. It is a new method for inverting environmental parameters with better inversion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The time-distance domain sound pressure data recorded by a single shot used in the implementation case of the present invention.

[0056] Figure 2 To transform Figure 1 The data in the time-distance domain are transformed into the frequency-wavenumber domain, and the data are modally filtered using the fk transform, retaining only the first-order hydroacoustic mode and the first-order geoacoustic mode.

[0057] Figure 3 It is the time-distance domain data after modal filtering and the corresponding interference structure.

[0058] Figure 4 Interference fringe curve extracted from experimental data and its slope change.

[0059] Figure 5 It is a posterior probability distribution diagram of the inversion result of the method of the present invention.

[0060] Figure 6 The interference structure calculated by the environmental model obtained by the method of the present invention and the interference fringe slope distribution law with frequency and data comparison diagram. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings 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.

[0062] Combination Figure 1-Figure 6 The present invention proposes a shallow seabed geoacoustic parameter inversion method based on very low frequency water-ground modal interference, the method comprising the following steps:

[0063] Step 1: Multiple hydrophones or OBS are deployed in the water, the ship sails, and then throws explosion sound sources or launches very low frequency airgun sound sources into the sea at fixed time intervals. After traversing the surveyed sea area, it returns and retrieves the receiving equipment to obtain sound pressure data in the time-distance domain;

[0064] Step 2: Perform preliminary processing and analysis on the sound pressure data in the time-distance domain. First, obtain the prior information of the ocean environment from the experimental data, determine the base sound velocity range using the propagation velocity of the base lateral wave, and then use the frequency-wavenumber domain characteristics to perform modal filtering to retain only the first-order water acoustic mode and the first-order ground acoustic mode with strong energy. Perform Fourier transform on the retained data to obtain the water-ground mode sound intensity interference structure in the distance-frequency domain.

[0065] Step 3: Extract the water-ground modal interference fringe curve in the distance-frequency domain of the experimental data, and calculate the distribution of the waveguide invariant with frequency using the following formula:

[0066]

[0067] Where: β represents the waveguide invariant, r0 represents the center distance between the sound source and the receiving point, f0 represents the center frequency, f represents the frequency, and r represents the distance;

[0068] Step 4: Theoretically calculate the variation of intermodal interference fringes with frequency. The specific calculation method is as follows:

[0069] On the distance-frequency plane, for a specific interference fringe, the sound intensity at each point on it is a constant, then:

[0070]

[0071] Where I represents the sound intensity, ω = 2πf is the angular frequency;

[0072] From the sound intensity expression we get:

[0073]

[0074]

[0075] Among them, m and n represent the order of the simple normal wave, A m and A n is the simple normal wave modal intensity, * represents the complex conjugate, Δk mn is the wave number difference between modes;

[0076] Substitute equation (3) and equation (4) into equation (2):

[0077]

[0078] Then we have:

[0079]

[0080] The theoretical expression of the fringe slope, i.e. the waveguide invariant of the two-order modal interference structure, is obtained as follows:

[0081]

[0082] Among them, β mn represents the waveguide invariant of the mth and nth order interference; I0 is a constant, S pm , S pn are the phase slowness of the m-order and n-order modes, S gm , S gn are the group slownesses of the m-order and n-order modes respectively;

[0083] From the above formula, we can know that the theoretical value of the waveguide invariant of the two-order modal interference structure is expressed as the ratio of the phase slowness difference between the modes to the group slowness difference. The phase velocity and group velocity dispersion curves can be obtained by using the acoustic field calculation software Kraken under the simple normal wave theory, that is, the distribution of the phase velocity and group velocity of each order of simple normal wave with frequency. Substituting into formula (7), we can obtain the distribution of the theoretical value of the waveguide invariant of the two-order modal interference structure with frequency β mn (f);

[0084] Step 5: Use the waveguide invariant β of water-ground modal interference mn Distribution with frequency as objective function in, The waveguide invariant representing the two-order modal interference structure extracted from the data is distributed over frequency, The theoretical calculated value is obtained by using Bayesian inversion optimization to calculate the cumulative minimum mean square error at multiple frequencies and obtain the minimum value of the objective function. At this time, the corresponding optimal value of the optimization parameter is the seabed parameter obtained by inversion.

[0085] The present invention also proposes a shallow sea bottom geoacoustic parameter inversion system based on very low frequency water-ground modal interference, the system comprising:

[0086] Data acquisition module: multiple hydrophones or OBS are deployed in the water, the ship sails, and then throws explosion sound sources or launches very low frequency airgun sound sources into the sea at fixed time intervals, traverses the surveyed sea area and returns, and retrieves the receiving equipment to obtain sound pressure data in the time-distance domain;

[0087] Data processing module: Preliminary processing and analysis of the sound pressure data in the time-distance domain. First, the prior information of the ocean environment is obtained from the experimental data. The propagation speed of the base side wave is used to determine the base sound speed range. Then, the frequency wavenumber domain characteristics are used to perform modal filtering to retain only the first-order water acoustic mode and the first-order ground acoustic mode with strong energy. The retained data is Fourier transformed to obtain the water-ground mode sound intensity interference structure in the distance-frequency domain.

[0088] Waveguide invariant calculation module: extract the water-ground modal interference fringe curve in the distance-frequency domain of the experimental data, and calculate the distribution of the waveguide invariant with frequency using the following formula:

[0089]

[0090] Where: β represents the waveguide invariant, r0 represents the center distance between the sound source and the receiving point, f0 represents the center frequency, f represents the frequency, and r represents the distance;

[0091] Theoretical calculation module: Theoretically calculate the change of intermodal interference fringes with frequency. The specific calculation method is as follows:

[0092] On the distance-frequency plane, for a specific interference fringe, the sound intensity at each point on it is a constant, then:

[0093]

[0094] Where I represents the sound intensity, ω = 2πf is the angular frequency;

[0095] From the sound intensity expression we get:

[0096]

[0097]

[0098] Among them, m and n represent the order of the simple normal wave, A m and A n is the simple normal wave modal intensity, * represents the complex conjugate, Δk mn is the wave number difference between modes;

[0099] Substitute equation (3) and equation (4) into equation (2):

[0100]

[0101] Then we have:

[0102]

[0103] The theoretical expression of the fringe slope, i.e. the waveguide invariant of the two-order modal interference structure, is obtained as follows:

[0104]

[0105] Among them, β mn represents the waveguide invariant of the mth and nth order interference; I0 is a constant, S pm , S pn are the phase slowness of the m-order and n-order modes, S gm , S gn are the group slownesses of the m-order and n-order modes respectively;

[0106] From the above formula, we can know that the theoretical value of the waveguide invariant of the two-order modal interference structure is expressed as the ratio of the phase slowness difference between the modes to the group slowness difference. The phase velocity and group velocity dispersion curves can be obtained by using the acoustic field calculation software Kraken under the simple normal wave theory, that is, the distribution of the phase velocity and group velocity of each order of simple normal wave with frequency. Substituting into formula (7), we can obtain the distribution of the theoretical value of the waveguide invariant of the two-order modal interference structure with frequency β mn (f);

[0107] Inversion Module: Waveguide Invariant β Using Water-Ground Modal Interference mn Distribution with frequency as objective function in, The waveguide invariant representing the two-order modal interference structure extracted from the data is distributed over frequency, The theoretical calculated value is obtained by using Bayesian inversion optimization to calculate the cumulative minimum mean square error at multiple frequencies and obtain the minimum value of the objective function. At this time, the corresponding optimal value of the optimization parameter is the seabed parameter obtained by inversion.

[0108] The present invention also proposes an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and is characterized in that when the processor executes the computer program, it implements the steps of the shallow seabed geoacoustic parameter inversion method based on very low frequency water-ground modal interference.

[0109] The present invention also proposes a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the shallow seabed geoacoustic parameter inversion method based on very low frequency water-ground modal interference.

[0110] The data for this implementation case comes from a multi-channel seismic exploration experiment (DL10-9) obtained in 2010 with a survey line of more than 100 kilometers from the Jiaolai Basin to the northern basin of the South Yellow Sea. The survey was conducted from east to west, with a water depth of 20-40m. The data was received by a towed array of 336 array elements, with a tow depth of 12m. The sound source has a total capacity of 2940in 3 The air gun array consists of 18 air guns, with a sound source depth of 8m and a firing interval of 37.5 meters.

[0111] The single shot data obtained is as follows: Figure 1 As shown in the figure, the water depth of the shot point is 30m. According to the above steps, the data is first analyzed to obtain the prior information of the experimental sea environment. Figure 1 As shown by the white dotted line in the middle, the propagation speed of the base side wave is about 4500m / s, and the optimal range of the base sound speed is determined to be 3000-6000m / s.

[0112] Then the data is transformed into the frequency wavenumber domain through fk transformation. Figure 2 As shown in the figure, the frequency wavenumber domain features are modally filtered. Under the condition of very low frequency at a depth of 30m, only the first-order hydroacoustic mode can be excited, and the other energy is coupled into the seabed and propagated as the ground acoustic mode. A filter is set in the wavenumber-frequency domain to retain only the hydroacoustic mode and ground acoustic mode with stronger energy. The filtered data is Fourier transformed to obtain the water-ground mode sound intensity interference structure in the distance-frequency domain. The filtered data and interference structure are shown in the figure. Figure 3 The extracted interference fringe curve and its slope change are shown in Figure 4 As shown. The maximum a posteriori probability model is solved by using the nonlinear global optimization algorithm - adaptive simplex simulated annealing (ASSA). The posterior probability density of some parameters is shown as follows Figure 5The inversion parameter prior interval and inversion results are shown in the following table:

[0113]

[0114]

[0115] The interference structure calculated by the environmental model obtained by the method of the present invention and the interference fringe slope distribution law with frequency are compared with the data. Figure 6 shown.

[0116] The present invention has achieved obvious results in typical implementation cases, and its advantages compared with the prior art are:

[0117] (1) By utilizing the special interference structure of the hydroacoustic mode and the geoacoustic mode, the shallow seabed geoacoustic parameters are inverted through experimental data processing and seabed modeling simulation. This interference characteristic is closely related to the dispersion of the seabed propagation mode and is a more sensitive physical quantity for inverting geoacoustic parameters.

[0118] (2) The experimental data obtained in the present invention has a high signal-to-noise ratio, and the cost function is more sensitive to changes in geoacoustic parameters. Therefore, the inversion is more efficient and the inverted geoacoustic parameters are more accurate.

[0119] When considering the propagation of very low frequency sound in a stratified shallow sea environment, part of the energy is coupled into the seabed to capture the geoacoustic mode propagation in the sediment layer. The water acoustic mode group velocity is negatively dispersed and the geoacoustic mode is positively dispersed. Therefore, the interference structure of the two is no longer in the form of stripes, but changes nonlinearly with frequency. This special interference structure is related to the modal propagation and dispersion characteristics in the sediment layer, and the dispersion characteristics are related to the acoustic parameters of the water body and the seabed. Therefore, it is a new method for inverting environmental parameters with better inversion effect. The present invention provides a specific process for inverting geoacoustic parameters using the interference characteristics of water and earth modes, and illustrates the effectiveness of the method with an implementation case. Compared with the prior art, its superiority lies in: because the cost function selected by the present invention is more sensitive to changes in geoacoustic parameters, the inversion is more efficient and the inverted geoacoustic parameters are more accurate.

[0120] The above is a detailed introduction to the shallow seabed geoacoustic parameter inversion method, system, equipment and medium based on very low frequency water-ground modal interference proposed in the present invention. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for general technical personnel in this field, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A shallow seabed geoacoustic parameter inversion method based on very low frequency water-ground modal interferometry, characterized in that: The method comprises the following steps: Step 1: Multiple hydrophones or OBS are deployed in the water, the ship sails, and then throws explosion sound sources or launches very low frequency airgun sound sources into the sea at fixed time intervals. After traversing the surveyed sea area, it returns and retrieves the receiving equipment to obtain sound pressure data in the time-distance domain; Step 2: Perform preliminary processing and analysis on the sound pressure data in the time-distance domain. First, obtain the prior information of the ocean environment from the experimental data, determine the base sound velocity range using the propagation velocity of the base lateral wave, and then use the frequency-wavenumber domain characteristics to perform modal filtering to retain only the first-order water acoustic mode and the first-order ground acoustic mode with strong energy. Perform Fourier transform on the retained data to obtain the water-ground mode sound intensity interference structure in the distance-frequency domain. Step 3: Extract the water-ground modal interference fringe curve in the distance-frequency domain of the experimental data, and calculate the distribution of the waveguide invariant with frequency using the following formula: Where: β represents the waveguide invariant, r0 represents the center distance between the sound source and the receiving point, f0 represents the center frequency, f represents the frequency, and r represents the distance; Step 4: Theoretically calculate the variation of intermodal interference fringes with frequency. The specific calculation method is as follows: On the distance-frequency plane, for a specific interference fringe, the sound intensity at each point on it is a constant, then: Where I represents the sound intensity, ω = 2πf is the angular frequency; From the sound intensity expression we get: Among them, m and n represent the order of the simple normal wave, A m and A n is the simple normal wave modal intensity, * represents the complex conjugate, Δk mn is the wave number difference between modes; Substitute equation (3) and equation (4) into equation (2): Then we have: The theoretical expression of the fringe slope, i.e. the waveguide invariant of the two-order modal interference structure, is obtained as follows: Among them, β mn represents the waveguide invariant of the mth and nth order interference; I0 is a constant, S pm , S pn are the phase slowness of the m-order and n-order modes, S gm , S gn are the group slownesses of the m-order and n-order modes respectively; From the above formula, we can know that the theoretical value of the waveguide invariant of the two-order modal interference structure is expressed as the ratio of the phase slowness difference between the modes to the group slowness difference. The phase velocity and group velocity dispersion curves can be obtained by using the acoustic field calculation software Kraken under the simple normal wave theory, that is, the distribution of the phase velocity and group velocity of each order of simple normal wave with frequency. Substituting into formula (7), we can obtain the distribution of the theoretical value of the waveguide invariant of the two-order modal interference structure with frequency β mn (f); Step 5: Use the waveguide invariant β of water-ground modal interference mn Distribution with frequency as objective function in, The waveguide invariant representing the two-order modal interference structure extracted from the data is distributed over frequency, The theoretical calculated value is obtained by using Bayesian inversion optimization to calculate the cumulative minimum mean square error at multiple frequencies and obtain the minimum value of the objective function. At this time, the corresponding optimal value of the optimization parameter is the seabed parameter obtained by inversion.

2. A shallow seabed geoacoustic parameter inversion system based on very low frequency water-ground modal interferometry, characterized in that: The system comprises: Data acquisition module: multiple hydrophones or OBS are deployed in the water, the ship sails, and then throws explosion sound sources or launches very low frequency airgun sound sources into the sea at fixed time intervals, traverses the surveyed sea area and returns, and retrieves the receiving equipment to obtain sound pressure data in the time-distance domain; Data processing module: Preliminary processing and analysis of the sound pressure data in the time-distance domain. First, the prior information of the ocean environment is obtained from the experimental data. The propagation speed of the base side wave is used to determine the base sound speed range. Then, the frequency wavenumber domain characteristics are used to perform modal filtering to retain only the first-order water acoustic mode and the first-order ground acoustic mode with strong energy. The retained data is Fourier transformed to obtain the water-ground mode sound intensity interference structure in the distance-frequency domain. Waveguide invariant calculation module: extract the water-ground modal interference fringe curve in the distance-frequency domain of the experimental data, and calculate the distribution of the waveguide invariant with frequency using the following formula: Where: β represents the waveguide invariant, r0 represents the center distance between the sound source and the receiving point, f0 represents the center frequency, f represents the frequency, and r represents the distance; Theoretical calculation module: Theoretically calculate the change of intermodal interference fringes with frequency. The specific calculation method is as follows: On the distance-frequency plane, for a specific interference fringe, the sound intensity at each point on it is a constant, then: Where I represents the sound intensity, ω = 2πf is the angular frequency; From the sound intensity expression we get: Among them, m and n represent the order of the simple normal wave, A m and A n is the simple normal wave modal intensity, * represents the complex conjugate, Δk mn is the wave number difference between modes; Substitute equation (3) and equation (4) into equation (2): Then we have: The theoretical expression of the fringe slope, i.e. the waveguide invariant of the two-order modal interference structure, is obtained as follows: Among them, β mn represents the waveguide invariant of the mth and nth order interference; I0 is a constant, S pm , S pn are the phase slowness of the m-order and n-order modes, S gm , S gn are the group slownesses of the m-order and n-order modes respectively; From the above formula, we can know that the theoretical value of the waveguide invariant of the two-order modal interference structure is expressed as the ratio of the phase slowness difference between the modes to the group slowness difference. The phase velocity and group velocity dispersion curves can be obtained by using the acoustic field calculation software Kraken under the simple normal wave theory, that is, the distribution of the phase velocity and group velocity of each order of simple normal wave with frequency. Substituting into formula (7), we can obtain the distribution of the theoretical value of the waveguide invariant of the two-order modal interference structure with frequency β mn (f); Inversion module: The waveguide invariant β of water-ground modal interferometry will be used mn Distribution with frequency as objective function in, The waveguide invariant representing the two-order modal interference structure extracted from the data is distributed over frequency, The theoretical calculated value is obtained by using Bayesian inversion optimization to calculate the cumulative minimum mean square error at multiple frequencies and obtain the minimum value of the objective function. At this time, the corresponding optimal value of the optimization parameter is the seabed parameter obtained by inversion.

3. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to claim 1 are implemented.

4. A computer-readable storage medium for storing computer instructions, characterized in that: When the computer instructions are executed by a processor, the steps of the method of claim 1 are implemented.

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