A method for obtaining seafloor geoacoustic parameters in continental slope areas based on the formation mechanism of sedimentary layers

Abstract

The invention discloses a method for acquiring seafloor geoacoustic parameters of a continental slope sea area based on a sedimentary layer formation mechanism, comprising: step 1) selecting an isobath from a continental slope sea area to be detected, and then determining a S1S3 survey line parallel to the isobath direction and a S2S4 survey line perpendicular to the isobath direction; the two survey lines intersect at a midpoint O1 of the survey lines; step 2) acquiring seafloor geoacoustic parameters on the S1S3 survey line according to the uniform distribution characteristics of the seafloor acoustic parameters on the S1S3 survey line, thereby obtaining seafloor geoacoustic parameters of the midpoint O1; step 3) calculating seafloor geoacoustic parameters on the S2S4 survey line in sections according to the seafloor geoacoustic parameters of the midpoint O1 and the section distribution characteristics of the seafloor geoacoustic parameters on the S2S4 survey line; step 4) expanding each section of seafloor geoacoustic parameters on the S2S4 survey line in a direction parallel to the isobath direction according to the uniform distribution characteristics of the seafloor geoacoustic parameters parallel to the isobath direction, and acquiring seafloor geoacoustic parameters of the continental slope sea area to be detected from sections to belts, and from belts to surfaces.

Description

Technical Field

[0001] The invention relates to the field of hydroacoustic physics, and in particular to a method for acquiring seabed geoacoustic parameters in a continental slope sea area based on a sedimentary layer formation mechanism. Background Art

[0002] Seabed acoustic parameters are extremely important in underwater target positioning, environmental monitoring, and other aspects. However, the continental slope transition area is an atypical deep-sea ocean environment, and the distribution of seabed sediment types varies. The direct on-site measurement method is difficult to meet the needs of quickly obtaining large-area seabed parameters in practical applications. Therefore, the use of acoustic inversion methods to obtain seabed geoacoustic parameters and conduct seabed geoacoustic modeling has attracted widespread attention from scholars at home and abroad. Currently, the commonly used geoacoustic inversion methods are the matching field inversion method and the least squares method of acoustic propagation loss, but they are all based on single points and single lines, and cannot quickly obtain large-area seabed geoacoustic parameters. Summary of the invention

[0003] The purpose of the present invention is to overcome the above-mentioned technical defects and propose a method for acquiring seabed geoacoustic parameters of a continental slope sea area based on the formation mechanism of a sedimentary layer. The method establishes a seabed geoacoustic model of a continental slope sea area based on the formation mechanism of a sedimentary layer, and ensures the interpretability and verifiability of the established seabed model with a clear physical meaning; firstly, through the traditional matching field and acoustic propagation loss least squares method, geoacoustic inversion is performed on the survey line parallel to the direction of the sea area isobath; secondly, based on the circum-continental distribution and annular belt distribution characteristics of the sedimentary layer, segmented geoacoustic inversion is performed on the survey line perpendicular to the direction of the sea area isobath; finally, based on the circum-continental distribution and annular belt distribution characteristics of the sedimentary layer, from segment to belt, from belt to surface, the acquisition of seabed geoacoustic parameters of a large area of ​​the continental slope sea area can be achieved.

[0004] To achieve the above purpose, the present invention proposes a method for acquiring seafloor geoacoustic parameters in a continental slope sea area based on the formation mechanism of a sedimentary layer, the method comprising:

[0005] Step 1) Select an isobath from the sea area of ​​the continental slope to be detected, and then determine the S1S3 survey line parallel to the isobath and the S2S4 survey line perpendicular to the isobath; the two survey lines intersect at the midpoint O1 of the survey lines;

[0006] Step 2) according to the uniform distribution characteristics of the seabed acoustic parameters on the S1S3 survey line, the seabed geoacoustic parameters on the S1S3 survey line are obtained, thereby obtaining the seabed geoacoustic parameters of the midpoint O1;

[0007] Step 3) according to the seabed geoacoustic parameters of the midpoint O1 and the segmented distribution characteristics of the seabed geoacoustic parameters on the S2S4 survey line, segmentally calculate the seabed geoacoustic parameters on the S2S4 survey line;

[0008] Step 4) According to the uniform distribution characteristics of the seabed geoacoustic parameters parallel to the isobaths, each section of the seabed geoacoustic parameters on the S2S4 survey line is expanded in the direction parallel to the isobaths, from section to belt, from belt to surface, so as to obtain the seabed geoacoustic parameters of the continental slope sea area to be detected.

[0009] As an improvement of the above method, the step 2) specifically includes:

[0010] The inversion of seabed geoacoustic parameters is to infer the seabed model parameters through the seabed information carried by the measurement data. Its cost function E1(m) is a broadband incoherent Bartlett matcher:

[0011]

[0012] Where m is the parameter vector to be inverted, including the thickness of the sedimentary layer, the acoustic velocity of the sedimentary layer and the acoustic velocity of the basement layer; N f represents the number of frequency points, H represents the complex conjugate transpose, and p n and q n (m) are the sound pressure field vector and copy field vector of the nth frequency point received by the vertical array;

[0013] When using broadband incoherent Bartlett matching, the empirical value of the seafloor attenuation coefficient is first used as the seafloor attenuation coefficient α; the search interval of m is given according to the empirical value of m, and the simulated annealing algorithm is used to search in the interval. When the cost function in formula (1) takes the minimum value, the value of m is the optimal solution of the parameter vector to be inverted;

[0014] Then the propagation loss least squares method is used to invert the seabed attenuation coefficient α: The optimal solution of m and the measured hydrological parameters are used as the input of the acoustic field model to obtain the propagation loss at different distances r and different frequencies of the numerical simulation. In addition, the propagation loss at different frequencies at distance r is calculated through offshore test data.

[0015] The cost function E2 is:

[0016]

[0017] in, and The average value of each frequency point on the 1 / 3 octave band respectively; N represents the total number of explosion sound sources on the survey line or survey section to be inverted, n represents the serial number of the explosion sound source, n = 1, 2...N; the initial value of the seabed attenuation coefficient α is an empirical value, and the traversal method is searched on the empirical interval of the α value. When the cost function E2 obtains the minimum value, the α value at this time is the optimal solution of the seabed attenuation coefficient;

[0018] The seabed acoustic parameters on the S1S3 survey line are the optimal solution of the parameter vector m to be inverted and the optimal solution of the seabed attenuation coefficient α, and the seabed acoustic parameters at point O1 are the seabed acoustic parameters on the S1S3 survey line.

[0019] As an improvement of the above method, the step 3) specifically includes:

[0020] Step 3-1) The seabed acoustic parameters of point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r1:

[0021] When r1=0, it is considered that the number of seabed layers at point O1 is insufficient to describe the actual seabed layers on the O1S2 survey line, and it is necessary to increase the seabed layers. This is because in sea areas with steeper slopes, the sound propagation problem needs to consider the sound lines with large grazing angles, and it is generally necessary to increase the seabed layers. Therefore, within the distance where the steep slope is greater than the second threshold, the seabed layers are increased. This distance is recorded as r1′, the corresponding measuring point is T1, and segment 1 is the measuring segment between points O1 and T1. Each additional layer of seabed layer i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the basis of the original one: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update m to m′, and then re-search c on segment 1 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the value of m′ and the optimal solution of the α value at point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 1 less than the third threshold; the optimal solution of the value of m′ and the α value at point O1 is the seabed acoustic parameter on segment 1;

[0022] When r1>0, the measurement point corresponding to the distance r1 is T1, which means that the seabed acoustic parameters have changed at point T1. Segment 1 is the measurement segment between points O1 and T1, and the seabed acoustic parameters on segment 1 are the seabed acoustic parameters at point O1.

[0023] Segment 2 is the measurement segment between point T1 and point S2. In the area of ​​segment 2, step 2) is re-executed: the optimal solution of the m value on segment 2 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 2 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the optimal solutions of the m value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 less than the third threshold, then the optimal solution of the m value and the α value on segment 2 is the seabed acoustic parameter of segment 2; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 2, and it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and then re-execute step 2): re-search c on segment 1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the optimal solution of the m′ value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value of the offshore test make the cost function E2 on segment 2 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 2;

[0024] Step 3-2) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than the first threshold at a certain distance and greater than the distance, this distance is recorded as r2, and the corresponding measuring point is T2, indicating that the seabed acoustic parameters have changed at point T2, and segment 2 is updated to the measuring segment between points T1 and T2, and segment 3 is the measuring segment between points T2 and S2; then point T2 is the "connection transition point" between "segments 2 and 3":

[0025] In the area of ​​segment 3, step 2) is re-executed: that is, the optimal solution of the m value on segment 3 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 3 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m value and the α value on segment 3, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment 3 is the seabed acoustic parameter of segment 3; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 3. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute step 2): re-search c on segment 3 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m′ value and the α value on segment 3 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 3;

[0026] Step 3-3) Let the initial value of the number of iterations j be 3;

[0027] Step 3-4) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the seabed acoustic parameters of segment j and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r j , the corresponding measuring point is Tj, indicating that the seabed acoustic parameters have changed here, and segment j is updated to the measuring segment between Tj-1 and Tj, and segment j+1 is the measuring segment between Tj and S2, that is, Tj is the "connection transition point" between "segment j and segment j+1", and step 3-5) is entered; if the absolute value of the difference between all simulated propagation loss values ​​and the measured propagation loss values ​​of the offshore test is not greater than the first threshold, step 3-6) is entered;

[0028] Step 3-5) On segment j+1, re-execute step 2): that is, re-find the optimal solution of the m value on segment j+1 through the cost function E1(m), and re-find the optimal solution of the α value on segment j+1 through the cost function E2; input the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m value and the α value of segment j+1, and the measured hydrological parameters on the O1S2 survey line into the acoustic field calculation model at the same time. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment j+1 is the seabed acoustic parameter of segment j+1; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment j+1. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute step 2): re-search c on segment j+1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m' value and the α value on segment j+1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold; at this time, the optimal solution of the m' value and the α value at point O1 is the seabed acoustic parameter on segment j+1; after j+1, go to step 3-4);

[0029] Step 3-6) The iteration ends, and the step-by-step seafloor acoustic parameters perpendicular to the zonal distribution on O1S2 are obtained;

[0030] Step 3-7) Obtain the seabed acoustic parameters on the O1S4 survey line in sections; thereby obtain the seabed acoustic parameters on the S2S4 survey line.

[0031] The present invention proposes a system for acquiring seafloor geoacoustic parameters in a continental slope sea area based on the formation mechanism of a sedimentary layer. The system comprises: a survey line determination module, a seafloor geoacoustic parameter calculation module for the S1S3 survey line, a seafloor geoacoustic parameter calculation module for the S2S4 survey line, and a seafloor geoacoustic parameter expansion module for the area to be detected;

[0032] The survey line determination module is used to select an isobath from the continental slope sea area to be detected, and then determine the S1S3 survey line parallel to the isobath direction and the S2S4 survey line perpendicular to the isobath direction; the two survey lines intersect at the midpoint O1 of the survey lines;

[0033] The S1S3 survey line seabed geoacoustic parameter calculation module is used to obtain the seabed geoacoustic parameters on the S1S3 survey line according to the uniform distribution characteristics of the seabed acoustic parameters on the S1S3 survey line, thereby obtaining the seabed geoacoustic parameters of the midpoint O1;

[0034] The S2S4 survey line seabed geoacoustic parameter calculation module is used to calculate the seabed geoacoustic parameters on the S2S4 survey line in sections according to the seabed geoacoustic parameters of the midpoint O1 and the section distribution characteristics of the seabed geoacoustic parameters on the S2S4 survey line;

[0035] The seabed geoacoustic parameter expansion module of the area to be detected is used to expand the seabed geoacoustic parameters of each section on the S2S4 survey line in the direction parallel to the isobath according to the characteristic that the seabed geoacoustic parameters are evenly distributed, from section to belt, from belt to surface, so as to obtain the seabed geoacoustic parameters of the continental slope sea area to be detected.

[0036] As an improvement of the above system, the specific implementation process of the S1S3 survey line seabed geoacoustic parameter calculation module includes:

[0037] The inversion of seabed geoacoustic parameters is to infer the seabed model parameters through the seabed information carried by the measurement data. Its cost function E1(m) is a broadband incoherent Bartlett matcher:

[0038]

[0039] Where m is the parameter vector to be inverted, including the thickness of the sedimentary layer, the acoustic velocity of the sedimentary layer and the acoustic velocity of the basement layer; N f represents the number of frequency points, H represents the complex conjugate transpose, and p n and q n (m) are the sound pressure field vector and copy field vector of the nth frequency point received by the vertical array;

[0040] When using broadband incoherent Bartlett matching, the empirical value of the seafloor attenuation coefficient is first used as the seafloor attenuation coefficient α; the search interval of m is given according to the empirical value of m, and the simulated annealing algorithm is used to search in the interval. When the cost function in formula (1) takes the minimum value, the value of m is the optimal solution of the parameter vector to be inverted;

[0041] Then the propagation loss least squares method is used to invert the seabed attenuation coefficient α: The optimal solution of m and the measured hydrological parameters are used as the input of the acoustic field model to obtain the propagation loss at different distances r and different frequencies of the numerical simulation. In addition, the propagation loss at different frequencies at distance r is calculated through offshore test data.

[0042] The cost function E2 is:

[0043]

[0044] in, and The average value of each frequency point on the 1 / 3 octave band respectively; N represents the total number of explosion sound sources on the survey line or survey section to be inverted, n represents the serial number of the explosion sound source, n = 1, 2...N; the initial value of the seabed attenuation coefficient α is an empirical value, and the traversal method is searched on the empirical interval of the α value. When the cost function E2 obtains the minimum value, the α value at this time is the optimal solution of the seabed attenuation coefficient;

[0045] The seabed acoustic parameters on the S1S3 survey line are the optimal solution of the parameter vector m to be inverted and the optimal solution of the seabed attenuation coefficient α, and the seabed acoustic parameters at point O1 are the seabed acoustic parameters on the S1S3 survey line.

[0046] As an improvement of the above system, the specific implementation process of the S2S4 survey line seabed geoacoustic parameter calculation module includes:

[0047] Step 3-1) The seabed acoustic parameters of point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r1:

[0048] When r1=0, within the distance where the steep slope is greater than the second threshold, the seafloor layer is added; and this distance is recorded as r1′, the corresponding measuring point is T1, and segment 1 is the measuring segment between point O1 and point T1; each additional layer of seafloor layer i, i≥3, is equivalent to adding two new elements to the seafloor parameter vector m on the basis of the original one: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update m to m′, and then re-search c on segment 1 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the value of m′ and the optimal solution of the α value at point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 1 less than the third threshold; the optimal solution of the value of m′ and the α value at point O1 is the seabed acoustic parameter on segment 1;

[0049] When r1>0, the measurement point corresponding to the distance r1 is T1, which means that the seabed acoustic parameters have changed at point T1. Segment 1 is the measurement segment between points O1 and T1, and the seabed acoustic parameters on segment 1 are the seabed acoustic parameters at point O1.

[0050] Segment 2 is the measurement segment between point T1 and point S2. In the area of ​​segment 2, step 2) is re-executed: the optimal solution of the m value on segment 2 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 2 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the optimal solutions of the m value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 less than the third threshold, then the optimal solution of the m value and the α value on segment 2 is the seabed acoustic parameter of segment 2; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 2, and it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and then re-execute step 2): re-search c on segment 1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the optimal solution of the m′ value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value of the offshore test make the cost function E2 on segment 2 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 2;

[0051] Step 3-2) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than the first threshold at a certain distance and greater than the distance, this distance is recorded as r2, and the corresponding measuring point is T2, indicating that the seabed acoustic parameters have changed at point T2, and segment 2 is updated to the measuring segment between points T1 and T2, and segment 3 is the measuring segment between points T2 and S2; then point T2 is the "connection transition point" between "segments 2 and 3":

[0052] In the area of ​​segment 3, step 2) is re-executed: that is, the optimal solution of the m value on segment 3 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 3 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m value and the α value on segment 3, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment 3 is the seabed acoustic parameter of segment 3; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 3. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute step 2): re-search c on segment 3 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m′ value and the α value on segment 3 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 3;

[0053] Step 3-3) Let the initial value of the number of iterations j be 3;

[0054] Step 3-4) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the seabed acoustic parameters of segment j and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r j , the corresponding measuring point is Tj, indicating that the seabed acoustic parameters have changed here, and segment j is updated to the measuring segment between Tj-1 and Tj, and segment j+1 is the measuring segment between Tj and S2, that is, Tj is the "connection transition point" between "segment j and segment j+1", and step 3-5) is entered; if the absolute value of the difference between all simulated propagation loss values ​​and the measured propagation loss values ​​of the offshore test is not greater than the first threshold, step 3-6) is entered;

[0055] Step 3-5) On segment j+1, re-execute step 2): that is, re-find the optimal solution of the m value on segment j+1 through the cost function E1(m), and re-find the optimal solution of the α value on segment j+1 through the cost function E2; input the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m value and the α value of segment j+1, and the measured hydrological parameters on the O1S2 survey line into the acoustic field calculation model at the same time. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment j+1 is the seabed acoustic parameter of segment j+1; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment j+1. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute step 2): re-search c on segment j+1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m' value and the α value on segment j+1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold; at this time, the optimal solution of the m' value and the α value at point O1 is the seabed acoustic parameter on segment j+1; after j+1, go to step 3-4);

[0056] Step 3-6) The iteration ends, and the step-by-step seafloor acoustic parameters perpendicular to the zonal distribution on O1S2 are obtained;

[0057] Step 3-7) Obtain the seabed acoustic parameters on the O1S4 survey line in sections; thereby obtain the seabed acoustic parameters on the S2S4 survey line.

[0058] The advantages of the present invention are:

[0059] 1. The method of the present invention starts from the formation mechanism of the sedimentary layer and ensures the interpretability and verifiability of the established seabed model with clear physical meaning;

[0060] 2. The method of the present invention combines the traditional geoacoustic inversion method with the formation mechanism of the sedimentary layer, which can ensure the accuracy of the established seabed model;

[0061] 3. The method of the present invention is based on the loop distribution and ring belt distribution characteristics of the sedimentary layer, combining lines and belts, and from belts to surfaces, it can realize the rapid acquisition of seabed geoacoustic parameters in a large area of ​​the continental slope sea area, reducing the time consumption and operation difficulties in actual experiments;

[0062] 4. The method of the present invention can quickly obtain seafloor acoustic parameters in a large range of continental slope sea areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is the experimental measurement line design diagram of the present invention;

[0064] Figure 2(a) is a seafloor topography map of the O1S1 survey line parallel to the isobath;

[0065] Figure 2(b) is a seafloor topography map of the O1S3 survey line parallel to the isobath;

[0066] Figure 3 It is a schematic diagram of the geoacoustic model on the survey line parallel to the isobath;

[0067] Figure 4 This is a schematic diagram of the seafloor geoacoustic model on the S1S3 survey line;

[0068] Figure 5 This is a schematic diagram of the attenuation coefficient on the S1S3 survey line;

[0069] Figure 6(a) is a seafloor topography map of the O1S2 survey line perpendicular to the isobath;

[0070] Figure 6(b) is a seafloor topography map of the O1S4 survey line perpendicular to the isobath;

[0071] Figure 7(a) is a schematic diagram of the seafloor inversion results of the O1S2 survey line;

[0072] Figure 7(b) is a schematic diagram of the seafloor inversion results of the O1S4 survey line;

[0073] Figure 8 A schematic diagram for quickly obtaining large-area seabed geoacoustic parameters by belt and surface;

[0074] Fig. 9 Schematic diagram of the comparison between the measured and simulated values ​​of propagation loss (TL) on the circular measurement line. DETAILED DESCRIPTION

[0075] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0076] The present invention proposes a method for acquiring seabed geoacoustic parameters in continental slope sea areas based on the formation mechanism of sedimentary layers. The method consists of three parts: experimental scheme design, geoacoustic inversion on the survey line, and rapid acquisition of large-area seabed geoacoustic parameters by belts and surfaces.

[0077] (1) Experimental design

[0078] ①Signal form:

[0079] 50m-1kg fixed depth explosion sound source signal

[0080] ② Experimental measurement line design

[0081] From geology, we know that the sedimentary layers in the continental slope sea area have a certain formation mechanism: the distribution of marine sediments is controlled by factors such as depth and distance from the land, thus showing the phenomenon of circumcontinental zoning and equal zoning. The zonation of marine sediments is a macroscopic phenomenon on a global scale. In the shallow sea at the continental margin, terrigenous clastic deposits are the main type; in the semi-deep sea area, there are both terrigenous materials and sediments formed by biological and chemical effects; in the deep sea area, it is mainly deep-sea deposits formed by biological and chemical effects. It can be seen from this that the sedimentary layers in the continental slope sea area will appear in a zonal distribution, and this zoning can be roughly considered to be circumcontinental distribution or parallel to the isobaths of the sea area. Based on this, the present invention designs the two main S1S3 survey lines and S2S4 survey lines in the experiment as survey lines parallel to the isobaths of the sea area and survey lines perpendicular to the isobaths of the sea area, respectively, such as Figure 1 As shown by the black line in the middle, the two lines intersect each other perpendicularly at the midpoint O1 of the line. In order to verify the ability of this method to quickly obtain large-area geoacoustic parameters and the accuracy of this method, a circular line in the area spanned by the two lines is finally designed, as shown in Figure 1 In addition, Figure 1 The depth contours of the sea areas are also marked.

[0082] ③ Experimental implementation process

[0083] A 32-element vertical receiving array was deployed at point O1. A 50m-1kg fixed-depth explosion sound source was placed along the survey line in the experimental design. During the experiment, hydrological environmental parameters such as CTD and XBT and seabed topography were measured simultaneously.

[0084] (2) Inversion of geoacoustic parameters along the survey line

[0085] ① Obtaining seafloor acoustic parameters on the S1S3 survey line parallel to the isobath

[0086] As shown in Figure 2(a) and Figure 2(b), the seafloor of the S1S3 survey line parallel to the isobath is relatively flat, and the sea depth is almost constant at 206m. Based on the circum-continental distribution of sedimentary layers in the continental slope sea area or the uniform distribution characteristics parallel to the isobaths in the sea area, it can be considered that in the direction parallel to the isobaths, the geoacoustic model is a uniform sedimentary layer (layer 1) covering a semi-infinite basement layer (layer 2), as shown in Figure 2(a). Figure 3As shown. The inversion of seabed geoacoustic parameters is to infer the seabed model parameters through the seabed information carried by the measurement data, and its cost function is a broadband incoherent Bartlett matcher:

[0087]

[0088] Where m is the parameter vector to be inverted, including the thickness of the sedimentary layer, the acoustic velocity of the sedimentary layer and the acoustic velocity of the basement layer; N f represents the number of frequency points, H represents the complex conjugate transpose, and p n and q n (m) are the sound pressure field vector and copy field vector of the nth frequency point received by the vertical array; the copy field can be obtained through sound field simulation calculation.

[0089] The inversion of seabed geoacoustic parameters generally includes four quantities: sediment thickness, sediment velocity, basement velocity and seabed attenuation coefficient α. Since the matching field processor is less sensitive to the attenuation coefficient α of the seabed, the propagation loss least square method is used to obtain the attenuation coefficient of the seabed. Therefore, m here includes three quantities: sediment thickness, sediment velocity and basement velocity. In addition, when using broadband incoherent Bartlett matching processing, the empirical value is first used as the seabed attenuation coefficient α; in addition, the search interval of m is given according to the empirical value, and the simulated annealing algorithm is used to search in the interval. When the cost function E1 in (1) takes the minimum value, the m value is the optimal solution for the parameters to be inverted (sediment thickness, sediment velocity and basement velocity).

[0090] Next, the propagation loss least squares method will be used to invert the seabed attenuation coefficient α: Taking the optimal solution of m and the measured hydrological parameters as the input of the acoustic field model, the propagation loss at different distances r and different frequencies of the numerical simulation can be obtained. In addition, the propagation loss at different frequencies at the same distance r can be calculated by calculating the offshore test data.

[0091] The cost function is:

[0092]

[0093] The propagation loss obtained by numerical simulation and test data is averaged over the 1 / 3 octave of each frequency point. N represents the total number of explosion sound sources on the survey line, n represents the nth explosion sound source on the survey line, and n = 1, 2…N. The initial value of α is an empirical value, and the traversal method can be searched on the empirical interval of α. When the cost function E2 obtains the minimum value, the α value at this time is the optimal solution for the seabed attenuation coefficient.

[0094] The thickness of the sediment layer, the acoustic velocity of the sediment layer and the acoustic velocity of the basement layer are inverted by the above matching field method; the seafloor attenuation coefficient is then inverted by the least squares method of propagation loss, and the seafloor acoustic parameters on the S1S3 survey line parallel to the isobath can be obtained. The results are as follows: Figure 4 and Figure 5 shown.

[0095] ② Obtaining seafloor acoustic parameters on the S2S4 survey line perpendicular to the depth contour

[0096] As shown in Figure 6(a) and Figure 6(b), the sea depth on the O1S2 and O1S4 lines perpendicular to the isobaths varies greatly. Since the distribution of marine sediments is controlled by factors such as depth and distance from land, the seabed acoustic parameters will change step by step on the S2S4 lines perpendicular to the isobaths. Figure 4 The inversion results in S2S4 and other measured hydrological parameters on the S2S4 survey line are simultaneously input into the acoustic field calculation model. When the propagation loss curve obtained by simulation is consistent with the measured propagation loss curve of the offshore test at a certain distance r j When there is a large difference in the distance r j The point is the "connection transition point" between "zone j and zone j+1" of the zonal distribution of sediments. Then, it is necessary to j Then, re-execute the steps in (2)① to obtain the seafloor acoustic parameters on the band j+1, j = 1, 2, 3, etc., and the seafloor acoustic parameters perpendicular to the zonal distribution on the O1S2 and O1S4 survey lines can be obtained. The results are as follows: Figure 7(a) and 7(b) shown.

[0097] The specific implementation process is:

[0098] Step 101) The seabed acoustic parameters of point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r1:

[0099] When r1=0, it is considered that the number of seabed layers at point O1 is insufficient to describe the actual seabed layers on the O1S2 survey line, and it is necessary to increase the seabed layers. This is because in sea areas with steeper slopes, the sound propagation problem needs to consider the sound lines with large grazing angles, and it is generally necessary to increase the seabed layers. Therefore, within the distance where the steep slope is greater than the second threshold, the seabed layers are increased. This distance is recorded as r1′, the corresponding measuring point is T1, and segment 1 is the measuring segment between points O1 and T1. Each additional layer of seabed layer i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the basis of the original one: the sound speed c in layer i iand the thickness h of layer i-1 i-1 , update m to m′, and then re-search c on segment 1 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the value of m′ and the optimal solution of the α value at point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 1 less than the third threshold; the optimal solution of the value of m′ and the α value at point O1 is the seabed acoustic parameter on segment 1;

[0100] When r1>0, the measurement point corresponding to the distance r1 is T1, which means that the seabed acoustic parameters have changed at point T1. Segment 1 is the measurement segment between points O1 and T1, and the seabed acoustic parameters on segment 1 are the seabed acoustic parameters at point O1.

[0101] Segment 2 is the measurement segment between point T1 and point S2. In the area of ​​segment 2, the steps in (2)① are re-executed: the optimal solution of the m value on segment 2 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 2 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the optimal solutions of the m value and α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 less than the third threshold, the optimal solution of the m value and α value on segment 2 is the seabed acoustic parameter of segment 2; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 2, and it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i ≥ 3, is equivalent to adding two new elements to the seabed parameter vector m on the basis of the original one: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and then re-execute the steps in (2)①: re-search for c on segment 1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the optimal solution of the m′ value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value of the offshore test make the cost function E2 on segment 2 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 2;

[0102] Step 102) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r2, and the corresponding measuring point is T2, indicating that the seabed acoustic parameters have changed at point T2, and segment 2 is updated to the measuring section between point T1 and point T2, and segment 3 is the measuring section between point T2 and point S2; then point T2 is the "connection transition point" between "segment 2 and segment 3":

[0103] In the area of ​​segment 3, the steps in (2)① are re-executed: that is, the optimal solution of the m value on segment 3 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 3 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solutions of the m value and the α value on segment 3, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment 3 is the seabed acoustic parameter of segment 3; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 3. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i ≥ 3, is equivalent to adding two new elements to the seabed parameter vector m on the basis of the original one: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute the step in (2)①: re-search for c on segment 3 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m′ value and the α value on segment 3 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 3;

[0104] Step 103) Let the initial value of the number of iterations j be 3;

[0105] Step 104) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the seabed acoustic parameters of segment j and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as rj , the corresponding measuring point is Tj, indicating that the seabed acoustic parameters have changed here, and segment j is updated to the measuring segment between Tj-1 and Tj, and segment j+1 is the measuring segment between Tj and S2, that is, Tj is the "connection transition point" between "segment j and segment j+1", and the process goes to step 105); if the absolute value of the difference between all simulated propagation loss values ​​and the measured propagation loss values ​​of the offshore test is not greater than the first threshold, the process goes to step 106);

[0106] Step 105) On segment j+1, re-execute the steps in (2)①: that is, re-find the optimal solution of the m value on segment j+1 through the cost function E1(m), and re-find the optimal solution of the α value on segment j+1 through the cost function E2; input the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m value and the α value of segment j+1, and the measured hydrological parameters on the O1S2 survey line into the acoustic field calculation model at the same time; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold value, it is considered that the optimal solution of the m value and the α value on segment j+1 is the seabed acoustic parameter of segment j+1; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 not less than the third threshold value, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment j+1, and it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the basis of the original one: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute the step in (2)①: re-search for c on segment j+1 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m' value and the α value on segment j+1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold value; at this time, the optimal solution of the m' value and the α value on point O1 is the seabed acoustic parameter on segment j+1; after j+1, go to step 104);

[0107] Step 106) The iteration ends, and the step-by-step seafloor acoustic parameters perpendicular to the zonal distribution on O1S2 are obtained;

[0108] Step 107) Acquire the seabed acoustic parameters on the O1S4 survey line in sections; thereby obtain the seabed acoustic parameters on the S2S4 survey line.

[0109] (3) Rapidly obtain large-area seabed geoacoustic parameters by segment and belt, and by belt and surface

[0110] Based on the circum-continental distribution of sedimentary layers in the continental slope sea area or the uniform distribution characteristics parallel to the depth contours of the sea area, it can be considered that in the direction parallel to the depth contours, the geoacoustic model is a uniform sedimentary layer covering a semi-infinite basement layer; while in the direction perpendicular to the depth contours, the geoacoustic parameters show a step-by-step change. Therefore, in the area covered by the two survey lines, the seabed geoacoustic parameters on the survey lines S2S4 perpendicular to the depth contours can be expanded in the direction of the depth contours, and the seabed geoacoustic parameters over a large range and area can be obtained from the belt to the surface. Figure 8 shown.

[0111] A circular survey line was specially designed in the experimental design to verify the accuracy of the method of the present invention and its ability to quickly obtain large-area geoacoustic parameters. The explosion sound source Exp on the circular survey line was obtained from the constructed annular distribution seabed geoacoustic model. k The geoacoustic parameters on the line connecting (k=1,2,3…) and the receiving array O1 point are used as the geoacoustic parameter input in the sound field model to simulate the propagation loss value on the circular survey line, which is consistent with the propagation loss value of the measured data. Fig. 9 The accuracy of the method of the present invention and its ability to quickly obtain large-area geoacoustic parameters have been verified.

[0112] Example 2

[0113] Embodiment 2 of the present invention proposes a system for acquiring seafloor geoacoustic parameters in a continental slope sea area based on the formation mechanism of a sedimentary layer, the system comprising: a survey line determination module, a seafloor geoacoustic parameter calculation module for the S1S3 survey line, a seafloor geoacoustic parameter calculation module for the S2S4 survey line, and a seafloor geoacoustic parameter expansion module for the area to be detected;

[0114] The survey line determination module is used to select an isobath from the continental slope sea area to be detected, and then determine the S1S3 survey line parallel to the isobath direction and the S2S4 survey line perpendicular to the isobath direction; the two survey lines intersect at the midpoint O1 of the survey lines;

[0115] The S1S3 survey line seabed geoacoustic parameter calculation module is used to obtain the seabed geoacoustic parameters on the S1S3 survey line according to the uniform distribution characteristics of the seabed acoustic parameters on the S1S3 survey line, thereby obtaining the seabed geoacoustic parameters of the midpoint O1;

[0116] The S2S4 survey line seabed geoacoustic parameter calculation module is used to calculate the seabed geoacoustic parameters on the S2S4 survey line in sections according to the seabed geoacoustic parameters of the midpoint O1 and the section distribution characteristics of the seabed geoacoustic parameters on the S2S4 survey line;

[0117] The seabed geoacoustic parameter expansion module of the area to be detected is used to expand the seabed geoacoustic parameters of each section on the S2S4 survey line in the direction parallel to the isobath according to the characteristic that the seabed geoacoustic parameters are evenly distributed, from section to belt, from belt to surface, so as to obtain the seabed geoacoustic parameters of the continental slope sea area to be detected.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A method for acquiring seafloor geoacoustic parameters in a continental slope sea area based on the formation mechanism of a sedimentary layer, the method comprising: Step 1) Select an isobath from the sea area of ​​the continental slope to be detected, and then determine the S1S3 survey line parallel to the isobath and the S2S4 survey line perpendicular to the isobath; the two survey lines intersect at the midpoint O1 of the survey lines; Step 2) according to the uniform distribution characteristics of the seabed acoustic parameters on the S1S3 survey line, the seabed geoacoustic parameters on the S1S3 survey line are obtained, thereby obtaining the seabed geoacoustic parameters of the midpoint O1; Step 3) according to the seabed geoacoustic parameters of the midpoint O1 and the segmented distribution characteristics of the seabed geoacoustic parameters on the S2S4 survey line, segmentally calculate the seabed geoacoustic parameters on the S2S4 survey line; Step 4) according to the uniform distribution characteristics of the seabed geoacoustic parameters parallel to the isobath direction, each section of the seabed geoacoustic parameters on the S2S4 survey line is expanded in the direction parallel to the isobath direction, from section to belt, from belt to surface, so as to obtain the seabed geoacoustic parameters of the continental slope sea area to be detected; The step 2) specifically includes: The inversion of seabed geoacoustic parameters is to infer the seabed model parameters through the seabed information carried by the measurement data. Its cost function E1(m) is a broadband incoherent Bartlett matcher: Where m is the parameter vector to be inverted, including the thickness of the sedimentary layer, the acoustic velocity of the sedimentary layer and the acoustic velocity of the basement layer; N f represents the number of frequency points, H represents the complex conjugate transpose, and p n and q n (m) are the sound pressure field vector and copy field vector of the nth frequency point received by the vertical array; When using broadband incoherent Bartlett matching, the empirical value of the seafloor attenuation coefficient is first used as the seafloor attenuation coefficient α; the search interval of m is given according to the empirical value of m, and the simulated annealing algorithm is used to search in the interval. When the cost function in formula (1) takes the minimum value, the value of m is the optimal solution of the parameter vector to be inverted; Then the propagation loss least squares method is used to invert the seabed attenuation coefficient α: The optimal solution of m and the measured hydrological parameters are used as the input of the acoustic field model to obtain the propagation loss at different distances r and different frequencies of the numerical simulation. In addition, the propagation loss at different frequencies at distance r is calculated through offshore test data. The cost function E2 is: in, and The average value of each frequency point on the 1 / 3 octave band respectively; N represents the total number of explosion sound sources on the survey line or survey section to be inverted, n represents the serial number of the explosion sound source, n = 1, 2...N; the initial value of the seabed attenuation coefficient α is an empirical value, and the traversal method is searched on the empirical interval of the α value. When the cost function E2 obtains the minimum value, the α value at this time is the optimal solution of the seabed attenuation coefficient; The seabed acoustic parameters on the S1S3 survey line are the optimal solution of the parameter vector m to be inverted and the optimal solution of the seabed attenuation coefficient α, and the seabed acoustic parameters at point O1 are the seabed acoustic parameters on the S1S3 survey line.

2. The method for acquiring seafloor geoacoustic parameters in a continental slope sea area based on the formation mechanism of a sedimentary layer according to claim 1, characterized in that: The step 3) specifically includes: Step 3-1) The seabed acoustic parameters of point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r1: When r1=0, within the distance where the steep slope is greater than the second threshold, the seafloor layer is added; and this distance is recorded as r1′, the corresponding measuring point is T1, and segment 1 is the measuring segment between point O1 and point T1; each additional layer of seafloor layer i, i≥3, is equivalent to adding two new elements to the seafloor parameter vector m on the basis of the original one: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update m to m′, and then re-search c on segment 1 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the value of m′ and the optimal solution of the α value at point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 1 less than the third threshold; the optimal solution of the value of m′ and the α value at point O1 is the seabed acoustic parameter on segment 1; When r1>0, the measurement point corresponding to the distance r1 is T1, which means that the seabed acoustic parameters have changed at point T1. Segment 1 is the measurement segment between points O1 and T1, and the seabed acoustic parameters on segment 1 are the seabed acoustic parameters at point O1. Segment 2 is the measurement segment between point T1 and point S2. In the area of ​​segment 2, step 2) is re-executed: the optimal solution of the m value on segment 2 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 2 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the optimal solutions of the m value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 less than the third threshold, then the optimal solution of the m value and the α value on segment 2 is the seabed acoustic parameter of segment 2; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 2, and it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and then re-execute step 2): re-search c on segment 1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the optimal solution of the m′ value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value of the offshore test make the cost function E2 on segment 2 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 2; Step 3-2) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than the first threshold at a certain distance and greater than the distance, this distance is recorded as r2, and the corresponding measuring point is T2, indicating that the seabed acoustic parameters have changed at point T2, and segment 2 is updated to the measuring segment between points T1 and T2, and segment 3 is the measuring segment between points T2 and S2; then point T2 is the "connection transition point" between "segment 2 and segment 3": In the area of ​​segment 3, step 2) is re-executed: that is, the optimal solution of the m value on segment 3 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 3 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m value and the α value on segment 3, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment 3 is the seabed acoustic parameter of segment 3; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 3. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute step 2): re-search c on segment 3 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m′ value and the α value on segment 3 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 3; Step 3-3) Let the initial value of the number of iterations j be 3; Step 3-4) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the seabed acoustic parameters of segment j and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r j , the corresponding measuring point is Tj, indicating that the seabed acoustic parameters have changed here, and segment j is updated to the measuring segment between Tj-1 and Tj, and segment j+1 is the measuring segment between Tj and S2, that is, Tj is the "connection transition point" between "segment j and segment j+1", and step 3-5) is entered; if the absolute value of the difference between all simulated propagation loss values ​​and the measured propagation loss values ​​of the offshore test is not greater than the first threshold, step 3-6) is entered; Step 3-5) On segment j+1, re-execute step 2): that is, re-find the optimal solution of the m value on segment j+1 through the cost function E1(m), and re-find the optimal solution of the α value on segment j+1 through the cost function E2; input the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m value and the α value of segment j+1, and the measured hydrological parameters on the O1S2 survey line into the acoustic field calculation model at the same time. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment j+1 is the seabed acoustic parameter of segment j+1; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment j+1. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute step 2): re-search c on segment j+1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m' value and the α value on segment j+1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold; at this time, the optimal solution of the m' value and the α value at point O1 is the seabed acoustic parameter on segment j+1; after j+1, go to step 3-4); Step 3-6) The iteration ends, and the step-by-step seafloor acoustic parameters perpendicular to the zonal distribution on O1S2 are obtained; Step 3-7) Obtain the seabed acoustic parameters on the O1S4 survey line in sections; thereby obtain the seabed acoustic parameters on the S2S4 survey line.

3. A system for acquiring seafloor geoacoustic parameters in the continental slope sea area based on the formation mechanism of sedimentary layers, characterized in that: The system comprises: a survey line determination module, a seabed geoacoustic parameter calculation module for the S1S3 survey line, a seabed geoacoustic parameter calculation module for the S2S4 survey line and a seabed geoacoustic parameter expansion module for the area to be detected; The survey line determination module is used to select an isobath from the continental slope sea area to be detected, and then determine the S1S3 survey line parallel to the isobath direction and the S2S4 survey line perpendicular to the isobath direction; the two survey lines intersect at the midpoint O1 of the survey lines; The S1S3 survey line seabed geoacoustic parameter calculation module is used to obtain the seabed geoacoustic parameters on the S1S3 survey line according to the uniform distribution characteristics of the seabed acoustic parameters on the S1S3 survey line, thereby obtaining the seabed geoacoustic parameters of the midpoint O1; The S2S4 survey line seabed geoacoustic parameter calculation module is used to calculate the seabed geoacoustic parameters on the S2S4 survey line in sections according to the seabed geoacoustic parameters of the midpoint O1 and the section distribution characteristics of the seabed geoacoustic parameters on the S2S4 survey line; The seabed geoacoustic parameter expansion module of the area to be detected is used to expand the seabed geoacoustic parameters of each section on the S2S4 survey line in the direction parallel to the isobath according to the characteristic that the seabed geoacoustic parameters are evenly distributed, from section to belt, from belt to surface, so as to obtain the seabed geoacoustic parameters of the continental slope sea area to be detected; The specific implementation process of the S1S3 survey line seabed geoacoustic parameter calculation module includes: The inversion of seabed geoacoustic parameters is to infer the seabed model parameters through the seabed information carried by the measurement data. Its cost function E1(m) is a broadband incoherent Bartlett matcher: Where m is the parameter vector to be inverted, including the thickness of the sedimentary layer, the acoustic velocity of the sedimentary layer and the acoustic velocity of the basement layer; N f represents the number of frequency points, H represents the complex conjugate transpose, and p n and q n (m) are the sound pressure field vector and copy field vector of the nth frequency point received by the vertical array; When using broadband incoherent Bartlett matching, the empirical value of the seafloor attenuation coefficient is first used as the seafloor attenuation coefficient α; the search interval of m is given according to the empirical value of m, and the simulated annealing algorithm is used to search in the interval. When the cost function in formula (1) takes the minimum value, the value of m is the optimal solution of the parameter vector to be inverted; Then the propagation loss least squares method is used to invert the seabed attenuation coefficient α: The optimal solution of m and the measured hydrological parameters are used as the input of the acoustic field model to obtain the propagation loss at different distances r and different frequencies of the numerical simulation. In addition, the propagation loss at different frequencies at distance r is calculated through offshore test data. The cost function E2 is: in, and The average value of each frequency point on the 1 / 3 octave band respectively; N represents the total number of explosion sound sources on the survey line or survey section to be inverted, n represents the serial number of the explosion sound source, n = 1, 2...N; the initial value of the seabed attenuation coefficient α is an empirical value, and the traversal method is searched on the empirical interval of the α value. When the cost function E2 obtains the minimum value, the α value at this time is the optimal solution of the seabed attenuation coefficient; The seabed acoustic parameters on the S1S3 survey line are the optimal solution of the parameter vector m to be inverted and the optimal solution of the seabed attenuation coefficient α, and the seabed acoustic parameters at point O1 are the seabed acoustic parameters on the S1S3 survey line.

4. The system for acquiring seafloor geoacoustic parameters in a continental slope sea area based on the formation mechanism of sedimentary layers according to claim 3 is characterized in that: The specific implementation process of the S2S4 survey line seabed geoacoustic parameter calculation module includes: Step 3-1) The seabed acoustic parameters of point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r1: When r1=0, within the distance where the steep slope is greater than the second threshold, the seafloor layer is added; and this distance is recorded as r1′, the corresponding measuring point is T1, and segment 1 is the measuring segment between point O1 and point T1; each additional layer of seafloor layer i, i≥3, is equivalent to adding two new elements to the seafloor parameter vector m on the basis of the original one: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update m to m′, and then re-search c on segment 1 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the value of m′ and the optimal solution of the α value at point O1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 1 less than the third threshold; the optimal solution of the value of m′ and the α value at point O1 is the seabed acoustic parameter on segment 1; When r1>0, the measurement point corresponding to the distance r1 is T1, which means that the seabed acoustic parameters have changed at point T1. Segment 1 is the measurement segment between points O1 and T1, and the seabed acoustic parameters on segment 1 are the seabed acoustic parameters at point O1. Segment 2 is the measurement segment between point T1 and point S2. In the area of ​​segment 2, step 2) is re-executed: the optimal solution of the m value on segment 2 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 2 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the optimal solutions of the m value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 less than the third threshold, then the optimal solution of the m value and the α value on segment 2 is the seabed acoustic parameter of segment 2; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 2 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 2, and it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and then re-execute step 2): re-search c on segment 1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the optimal solution of the m′ value and the α value on segment 2, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value of the offshore test make the cost function E2 on segment 2 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 2; Step 3-2) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than the first threshold at a certain distance and greater than the distance, this distance is recorded as r2, and the corresponding measuring point is T2, indicating that the seabed acoustic parameters have changed at point T2, and segment 2 is updated to the measuring segment between points T1 and T2, and segment 3 is the measuring segment between points T2 and S2; then point T2 is the "connection transition point" between "segment 2 and segment 3": In the area of ​​segment 3, step 2) is re-executed: that is, the optimal solution of the m value on segment 3 is re-searched through the cost function E1(m), and the optimal solution of the α value on segment 3 is re-searched through the cost function E2; the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m value and the α value on segment 3, and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment 3 is the seabed acoustic parameter of segment 3; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment 3. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute step 2): re-search c on segment 3 using the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, the optimal solution of the m′ value and the α value on segment 3 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment 3 less than the third threshold; at this time, the optimal solution of the m′ value and the α value on point O1 is the seabed acoustic parameter on segment 3; Step 3-3) Let the initial value of the number of iterations j be 3; Step 3-4) The seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the seabed acoustic parameters of segment j and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model to obtain a simulated propagation loss curve; when the absolute value of the difference between the simulated propagation loss value and the measured propagation loss value is greater than a first threshold at a certain distance and greater than the distance, this distance is recorded as r j , the corresponding measuring point is Tj, indicating that the seabed acoustic parameters have changed here, and segment j is updated to the measuring segment between Tj-1 and Tj, and segment j+1 is the measuring segment between Tj and S2, that is, Tj is the "connection transition point" between "segment j and segment j+1", and step 3-5) is entered; if the absolute value of the difference between all simulated propagation loss values ​​and the measured propagation loss values ​​of the offshore test is not greater than the first threshold, step 3-6) is entered; Step 3-5) On segment j+1, re-execute step 2): that is, re-find the optimal solution of the m value on segment j+1 through the cost function E1(m), and re-find the optimal solution of the α value on segment j+1 through the cost function E2; input the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m value and the α value of segment j+1, and the measured hydrological parameters on the O1S2 survey line into the acoustic field calculation model at the same time. When the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold, it is considered that the optimal solution of the m value and the α value on segment j+1 is the seabed acoustic parameter of segment j+1; when the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 not less than the third threshold, it is considered that the seabed stratification at this time is insufficient to describe the actual seabed stratification on segment j+1. At this time, it is necessary to increase the seabed stratification. Each additional layer of seabed stratification i, i≥3, is equivalent to adding two new elements to the seabed parameter vector m on the original basis: the sound speed c in layer i i and the thickness h of layer i-1 i-1 , update the value of m to m′, and re-execute step 2): re-search c on segment j+1 through the cost function E1(m′) i Value and h i-1 The optimal solution of the value is continuously iterated until the seabed acoustic parameters of segment 1, the seabed acoustic parameters of segment 2, ..., the optimal solution of the m' value and the α value on segment j+1 and the measured hydrological parameters on the O1S2 survey line are simultaneously input into the acoustic field calculation model, and the obtained simulated propagation loss value and the measured propagation loss value make the cost function E2 on segment j+1 less than the third threshold; at this time, the optimal solution of the m' value and the α value at point O1 is the seabed acoustic parameter on segment j+1; after j+1, go to step 3-4); Step 3-6) The iteration ends, and the step-by-step seafloor acoustic parameters perpendicular to the zonal distribution on O1S2 are obtained; Step 3-7) Obtain the seabed acoustic parameters on the O1S4 survey line in sections; thereby obtain the seabed acoustic parameters on the S2S4 survey line.

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