Ultra-wide coverage method and system for deepwater near-bottom multi-beam sonar

Abstract

The invention provides an ultra-wide coverage method and system for deepwater near-bottom multi-beam sonar. The method comprises the following steps: performing low-pass filtering on data acquired by a receiving transducer to obtain an analytic signal; performing near-field focusing on the analytic signal; performing windowing conventional beam forming on all the array elements to obtain a water body image; the method comprises the following steps: dividing an array element into P sub-arrays which are overlapped in space, and performing windowing conventional beam forming on each sub-array; constructing an amplitude-phase method time window; adopting a weighted time averaging method to obtain a TOA value under an amplitude method; calculating an interference pattern after each sub-array beam is formed; calculating a linear phase interval of an interferogram between each sub-array; carrying out weighted average on the interferogram to find a corresponding amplitude value in the water body; obtaining a phase difference according to the interferogram after weighted smoothing; and calculating the horizontal distance and depth of each ping, and circularly executing the operation. The method has the advantages that the method can adapt to more complex terrains while ensuring ultra-wide coverage.

Description

Technical Field

[0001] The present application belongs to the field of sonar technology, and specifically relates to an ultra-wide coverage method and system for deep-water near-bottom multi-beam sonar. Background Art

[0002] Deepwater near-bottom multi-beam sonar can work in waters of thousands or even tens of thousands of meters deep, and can achieve ultra-wide water depth coverage of 5 to 5.5 times at altitudes ranging from 20 to 200 meters from the bottom. At present, deepwater near-bottom multi-beam sonars mostly use amplitude-phase joint detection methods for seafloor mapping. Since the seafloor backscattering contribution is large and the echo energy is strong near the area directly below, the amplitude method is generally used near the area directly below; while for the seafloor far from the area directly below, the propagation loss is large, the echo duration is long, and the energy is weak, so the phase method is generally considered. Among them, the amplitude method uses the weighted time average method, and the phase method generally refers to the split subarray method.

[0003] This amplitude-phase joint estimation method can obtain relatively satisfactory results when the seabed terrain is relatively flat. However, when the seabed terrain is rugged, the effect of this method is often unsatisfactory. This is because the phase method only uses two sub-arrays. When the seabed terrain becomes complex, the overall variance of the data is large, and the use of two sub-arrays cannot reduce the variance by averaging. At the same time, the time window of the amplitude-phase joint detection method is related to the central beam water depth. When facing complex terrain, the central beam water depth between adjacent pings has significant changes. If the central beam water depth is not accurately calculated, a large amount of depth measurement errors will also occur. Summary of the invention

[0004] The purpose of this application is to overcome the defect that the prior art cannot adapt to the complex seabed terrain.

[0005] In order to achieve the above objectives, the present application proposes an ultra-wide coverage method for deep-water near-bottom multi-beam sonar, comprising:

[0006] Step 1: low-pass filter the real and imaginary raw data collected by the receiving transducer to obtain the analytical signal;

[0007] Step 2: Perform near-field focusing on the analytical signal to compensate for the phase error when the sound wave diffuses as a spherical wave;

[0008] Step 3: Perform windowed conventional beamforming on all array elements on the analytical signal after near-field focusing to obtain a water body image;

[0009] Step 4: Divide all array elements into P spatially overlapping sub-arrays, with a spacing of half a wavelength between each sub-array, and perform windowed conventional beamforming on each sub-array;

[0010] Step 5: Construct the amplitude-phase method time window;

[0011] Step 6: In a given time window, use the weighted time average method within the set beam opening angle to obtain the TOA value under the amplitude method;

[0012] Step 7: Calculate the interference pattern after beamforming of each sub-array;

[0013] Step 8: Calculate the linear phase interval of each inter-subarray interference pattern;

[0014] Step 9: Use the amplitude information in the water body map to perform weighted averaging on the interference pattern, and find the corresponding amplitude value in the water body according to each index value;

[0015] Step 10: Obtain the phase difference according to the weighted smoothed interference pattern;

[0016] Step 11: Calculate the horizontal distance and depth of each ping; calculate the central beam water depth and input it into the next ping, and repeat the above operation in a loop.

[0017] As an improvement of the above method, step 2 comprises:

[0018] The analytical signal expression after near-field focusing is:

[0019] S Fresnel =S filter *exp(-jΔφ Fresnel )

[0020] Among them, S filter is the analytical signal after low-pass filtering; S Fresnel is the analytical signal after near-field focusing; Δφ Fresnel is the phase compensation factor for near-field focusing:

[0021]

[0022] Where r is the distance from the center element to the seabed; Δx n is the offset between other elements and the central element on the receiving array; λ is the signal wavelength.

[0023] As an improvement of the above method, step 3 comprises:

[0024] Beamforming is performed on the analytical signal after near-field focusing, and the side lobes are suppressed by adding a Hamming window. The beam pointing angle is set to 0°, and the expression of all array elements after beamforming is obtained as follows:

[0025] B a =∑S Fresnel*exp(-j2π(n-1)d sin(θ0) / λ).*hamming(M),n=0,1,2,...N-1

[0026] Where N is the number of array elements; d is the array element spacing; θ0 is the beamforming pointing angle; M is the number of sampling points; B a The full array beam output data of all array elements; E a is a water body diagram; (·). The subscript operator in the middle represents the multiplication of each element of the vector separately;

[0027] hamming(M) is the Hamming window, expressed as:

[0028]

[0029] The water body map is obtained by beamforming all array elements, and its expression is:

[0030] E a =|B a | 2 .

[0031] The step 4 comprises:

[0032] Divide all array elements into P equally spaced subarrays, with each subarray spaced at λ / 2, and obtain the beamforming data B for each subarray pi for:

[0033]

[0034] As an improvement of the above method, step 5 comprises:

[0035] The time window expression of the amplitude-phase method is:

[0036] W(k)=T+2H ref (k) / c*tan(|A0(k)|+α) / cos(|A0(k)|-α),k=1,2,3,...K

[0037] Where W(k) represents the time window of the kth ping; T is the signal pulse width; H ref (k) is the central beam water depth of the kth ping iteration; c is the sound speed; K is the number of pings; α is the time window margin; A0(k) is the kth ping beam angle.

[0038] As an improvement of the above method, step 6 includes:

[0039] TOA value under amplitude method a The expression is:

[0040]

[0041] Among them, E a,t is the water body energy range within the time window, t min is the minimum value of the time window W(k), t max is the maximum value of the time window W(k), and t is the sampling point value in the time window.

[0042] As an improvement of the above method, step 7 includes:

[0043] Interference pattern P after beamforming of each subarray ij for:

[0044]

[0045] Among them, B pi is the beam output data of the i-th subarray, (.) H is the complex conjugate operator.

[0046] As an improvement of the above method, step 9 includes:

[0047] The interference pattern P after amplitude weighted smoothing ij smooth The expression is:

[0048]

[0049] in, represents the linear phase interval of the interference pattern between each sub-array; w a It is the amplitude information of the corresponding index value in the water body map.

[0050] As an improvement of the above method, step 10 includes:

[0051] According to the interference pattern after weighted smoothing Get the phase difference

[0052]

[0053] The quadratic fitting coefficients a0, a1, and a2 are calculated based on the smoothed phase difference, where a0 is the quadratic term coefficient, a1 is the linear term coefficient, and a2 is the constant term; the TOA value of each subarray under the phase method is obtained. Pij :

[0054]

[0055] Compare the two roots obtained from the quadratic equation and select the real part of the root closest to the time window as the result; when considering P subarrays, P-1 different TOA values ​​need to be calculated, and the average value of the P-1 TOA values ​​is calculated as the final total TOA value under the phase method. p , whose expression is:

[0056]

[0057] As an improvement of the above method, step 11 includes:

[0058] The horizontal distance X(n) and depth H(n) of each ping are:

[0059]

[0060] Where A0(n) represents the angle of the nth beam in 1 ping; R represents the number of waves;

[0061] The boundary between the amplitude method and the phase method is:

[0062]

[0063] The present application also provides an ultra-wide coverage system for deep-water near-bottom multi-beam sonar, which is implemented based on the above method, and the system includes:

[0064] The analytical signal acquisition module is used to perform low-pass filtering on the real and imaginary original data collected by the receiving transducer to obtain the analytical signal;

[0065] The near-field focusing module is used to perform near-field focusing on the analytical signal to compensate for the phase error when the sound wave diffuses as a spherical wave;

[0066] A water body image acquisition module is used to perform windowed conventional beamforming on all array elements on the analytical signal after near-field focusing to obtain a water body image;

[0067] A subarray division module is used to divide all array elements into P subarrays that overlap in space, with a spacing of half a wavelength between each subarray, and perform windowed conventional beamforming on each subarray;

[0068] Construct a time window module, which is used to construct the amplitude-phase method time window;

[0069] A module for obtaining the TOA value under the amplitude method is used to obtain the TOA value under the amplitude method by using a weighted time average method within a set beam opening angle in a given time window;

[0070] The interference pattern acquisition module is used to calculate the interference pattern of each sub-array after beamforming;

[0071] A linear phase interval acquisition module is used to calculate the linear phase interval of each interferogram between sub-arrays;

[0072] The amplitude value acquisition module is used to perform weighted averaging on the interference pattern using the amplitude information in the water body map, and find the corresponding amplitude value in the water body according to each index value;

[0073] A phase difference acquisition module is used to obtain a phase difference according to the interference pattern after weighted smoothing;

[0074] Get the horizontal distance and depth module to calculate the horizontal distance and depth of each ping.

[0075] Compared with the prior art, the advantages of this application are:

[0076] This application accurately calculates the central beam water depth through each ping iteration, and uses the amplitude information in the water body image after beamforming to perform weighted smoothing on the interference pattern. The method proposed in this application can adapt to more complex terrain while ensuring ultra-wide coverage. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 Shown is a flow chart of an ultra-wide coverage method for deep-water near-bottom multi-beam sonar;

[0078] Figure 2 The diagram shows the sub-array division;

[0079] Figure 3 Shown is a flat seabed water map of a certain sea area;

[0080] Figure 4 The method of the present invention and Figure 3 The fusion result map of water body map;

[0081] Figure 5 Shown is a picture of the rugged seabed water body in a certain sea area;

[0082] Figure 6 The figure shows the result of using the weighted time average-split subarray method and merging it with the water body map under the rugged seabed of a certain sea area;

[0083] Figure 7 The figure shows the result of using the method of the present invention and merging it with a water body map under the rugged seabed of a certain sea area. DETAILED DESCRIPTION

[0084] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0085] At present, the improvement of the amplitude-phase joint detection method is mainly in three aspects: the first is to improve the beamforming algorithm, such as the MVDR beamforming algorithm, which reduces the side lobes to improve the accuracy of the subsequent amplitude method; the second is to divide multiple subarrays, and reduce the variance of the data by averaging multiple subarrays to improve the accuracy of the phase method; the third is to smooth the complex interference pattern between subarrays by adding windows, and by smoothing the phase difference, the depth measurement accuracy can also be improved to a certain extent. For the third method, the use of windowed smoothing does not utilize the amplitude information in the data. Since the window parameters are fixed, multi-beam sonar will not obtain the optimal results when working under various seabed terrains. At the same time, the central beam water depth needs to be accurately calculated so that the time window can be iteratively adjusted according to different central beam water depths.

[0086] The present invention discloses an ultra-wide coverage method and system for deep-water near-bottom multi-beam sonar, which accurately calculates the central beam water depth through each ping iteration, and uses the amplitude information in the water body image after beamforming to perform weighted smoothing on the interference pattern. Compared with the existing methods, the method proposed by the present invention can adapt to more complex terrain while ensuring ultra-wide coverage.

[0087] Example 1

[0088] like Figure 1 As shown, the present invention provides an ultra-wide coverage method for deep-water near-bottom multi-beam sonar, comprising:

[0089] Step 1: Receive the real and imaginary raw data collected by the transducer and perform low-pass filtering to obtain the required analytical signal. The analytical signal is expressed as:

[0090] data_I filter =lowpass(data_I)

[0091] data_Q filter =lowpass(data_Q)

[0092] S filter =data_I filter +jdata_Q filter

[0093] Among them, data_I and data_Q are the real and imaginary signals of the original data.

[0094] Step 2: Perform near-field focusing on the analytical signal to compensate for the phase error when the sound wave diffuses as a spherical wave.

[0095] Due to the different heights of the deepwater near-bottom multi-beam sonar from the bottom, the distance each ping reaches the seabed is also different. When the sonar works in the near field, the sound waves spread in the form of spherical waves, resulting in different delays in the echo signals received by each element on the receiving array. Taking the center element of the receiving array as a reference (which can be considered to have the shortest echo delay), the distance from the center element to the seabed is r, and the offset between the other elements on the receiving array and the center element is recorded as Δx n , so the distance difference between different array elements and the seabed relative to the central array element is:

[0096]

[0097] Using Taylor's formula expansion, we can get:

[0098]

[0099] Therefore, the phase compensation factor for near-field focusing is:

[0100]

[0101] The analytical signal expression after near-field focusing is:

[0102] S Fresnel =S filter *exp(-jΔφ Fresnel )

[0103] Among them, S filter is the analytical signal after low-pass filtering, S Fresnel It is the analytical signal after near-field focusing.

[0104] Step 3: Perform windowed conventional beamforming on all array elements on the near-field focused analytical signal to obtain a water body image.

[0105] Beamforming is performed on the analytical signal after near-field focusing, and the side lobes are suppressed to a certain extent by adding a Hamming window. Assuming that the beam pointing angle is 0°, the expression of all array elements after beamforming is obtained as follows:

[0106] B a =∑S Fresnel *exp(-j2π(n-1)dsin(θ0) / λ).*hamming(M),n=0,1,2,...N-1

[0107] Where N is the number of array elements, d is the array element spacing, λ is the signal wavelength, θ0 is the beamforming pointing angle, M is the number of sampling points, and B a is the full array beam output data of all array elements, E a A water body map.

[0108] The Hamming window expression is:

[0109]

[0110] The water body map is obtained by beamforming all array elements, and its expression is:

[0111] E a =|B a | 2

[0112] Step 4: Divide all array elements into P sub-arrays that overlap in space, with a half-wavelength spacing between each sub-array, and perform windowed conventional beamforming on each sub-array. If the value of P is too small, the ideal effect cannot be achieved, and if it is too large, the amount of calculation will increase. The preferred value is 6.

[0113] like Figure 2 As shown, all array elements are divided into P equally spaced sub-arrays, each sub-array is spaced by λ / 2, and the beamforming data of each sub-array is obtained. Assuming there are N array elements, the beam data expression of each sub-array is:

[0114]

[0115] The subscript operator (·) indicates that each element of the vector is multiplied separately.

[0116] Step 5: Construct the amplitude-phase method time window, the expression is:

[0117] W(k)=T+2H ref (k) / c*tan(|A0(k)|+α) / cos(|A0(k)|-α),k=1,2,3,...K

[0118] Where W(k) represents the time window of the kth ping; T is the signal pulse width, H ref (k) is the water depth of the central beam of the k-th ping iteration, c is the sound speed, K is the number of pings, α is the time window margin, and the larger α is, the larger the window interval is. A0(k) is the beam angle of the k-th ping. Here, according to Figure 1 As shown, the first ping needs to input the a priori central beam water depth, that is, the current water depth information needs to be known in advance before the sonar starts working (of course, it does not need to be very accurate).

[0119] Step 6: In a given time window, use the weighted time average method within a certain beam angle to obtain the TOA value (signal arrival time) under the amplitude method. a .

[0120] According to the selected time window length and the full array beam data obtained after beamforming, the TOA value TOA under the amplitude method is obtained by weighted time averaging. a The expression is:

[0121]

[0122] Among them, E a,t is the water body energy range within the time window, t min is the minimum value of the time window W(k), t max is the maximum value of the time window W(k), and t is the sampling point value in the time window.

[0123] Step 7: Calculate the interference pattern of each sub-array after beamforming, and its expression is:

[0124]

[0125] Among them, B pi is the beam output data of the i-th subarray, (.) H is the complex conjugate operator.

[0126] Step 8: Calculate the linear phase interval of each interferogram between sub-arrays and record the linear phase starting index as s idx , the end index is recorded as e idx , the linear phase interval expression of each interferogram between sub-arrays is:

[0127]

[0128] Step 9: Use the amplitude information in the water body map to perform weighted averaging on the interference map, and find the corresponding amplitude value in the water body according to each index value. Therefore, the expression of the interference map after amplitude weighted smoothing is:

[0129]

[0130] Among them, w a The amplitude information of the corresponding index value in the water body map:

[0131] w a =E a (s idx :e idx )

[0132] Step 10: Obtain the phase difference based on the weighted smoothed interference pattern, which is expressed as:

[0133]

[0134] The quadratic fitting coefficients a0, a1, a2 are calculated based on the smoothed phase difference:

[0135] φ(t)=a0t 2 +a1t+a2

[0136] Get the TOA value of each subarray under the phase method Pij , whose expression is:

[0137]

[0138] The two roots obtained by the quadratic equation are compared, and the real part of the root closest to the time window is selected as the result. When considering P subarrays, P-1 different TOA values ​​need to be calculated, and the average value of the P-1 TOA values ​​is calculated as the final total TOA value under the phase method. p , whose expression is:

[0139]

[0140] Step 11: Assuming that each ping has a total of R beams (R is preferably 512), according to the TOA obtained above a with TOA p Calculate the horizontal distance and depth of each ping, the expression is:

[0141]

[0142] Where A0(n) represents the angle of the nth beam in 1 ping.

[0143] The boundary between the amplitude method and the phase method is:

[0144]

[0145] At the same time, the calculated central beam water depth H ref =H(R / 2) is input to the next ping, and the above operation is repeated.

[0146] By iteratively and accurately calculating the central beam water depth of each ping and using the amplitude information in the water body map to perform weighted smoothing of the interference pattern, it is possible to ensure ultra-wide coverage of deep-water near-bottom multi-beam sonar while adapting to more complex terrain.

[0147] The effectiveness of the algorithm of the present invention is verified by combining with actual sonar equipment. The deep-water near-bottom multi-beam sonar currently developed has been used in related projects. Through a series of pressure tests, it has been proved that the sonar can work in deep waters below 4500 meters or even 6000 meters. The sonar transmits CW signals with a signal pulse width T of 200us, an operating frequency f0 of 200kHz, and a sampling frequency f sThe frequency is 62.5kHz, the number of array elements N is 240, the number of beams is 512, the sound speed c is 1500m / s, the time window margin α is 10, the beam opening angle A0 is 140°, and the working distance is 200 meters.

[0148] like Figure 3 As shown, the water body map shows that the seabed is flat. Figure 4 , in order to merge the bottom map with the water map, the central beam water depth H ref It is about 46 meters. Figure 4 The maximum horizontal distances at the two ends are -112 meters and 133 meters respectively, which can be used to derive the maximum coverage width X of the sonar. max is 245 meters, so the coverage range expression is:

[0149]

[0150] The calculated Q is 5.3, which verifies the effectiveness of the ultra-wide coverage of the method of the present invention. Figure 5 As shown in the figure, the water body map shows a rugged seabed, which can be considered to be a complex seabed terrain. Figure 6 and Figure 7 By comparison, it can be seen that compared with the traditional weighted time average-split subarray method, the method of the present invention can effectively improve the accuracy of bathymetry. When the method of the present invention performs multi-subarray weighted smoothing, the smoothing window length L is 25. By using multiple subarrays and using the amplitude information in the water body map for weighted smoothing, the accuracy of bathymetry can be improved. Figure 6 , Figure 7 The red marked parts at both ends of Figure 6 The data points in become discrete, and Figure 7 After the method of the present invention is adopted, it is more consistent with the actual seabed topography and the continuity of data points is improved.

[0151] Example 2

[0152] The present application also provides an ultra-wide coverage system for deep-water near-bottom multi-beam sonar, which is implemented based on the above method, and the system includes:

[0153] The analytical signal acquisition module is used to perform low-pass filtering on the real and imaginary original data collected by the receiving transducer to obtain the analytical signal;

[0154] The near-field focusing module is used to perform near-field focusing on the analytical signal to compensate for the phase error when the sound wave diffuses as a spherical wave;

[0155] A water body image acquisition module is used to perform windowed conventional beamforming on all array elements on the analytical signal after near-field focusing to obtain a water body image;

[0156] A subarray division module is used to divide all array elements into P subarrays that overlap in space, with a spacing of half a wavelength between each subarray, and perform windowed conventional beamforming on each subarray;

[0157] Construct a time window module, which is used to construct the amplitude-phase method time window;

[0158] A module for obtaining the TOA value under the amplitude method is used to obtain the TOA value under the amplitude method by using a weighted time average method within a set beam opening angle in a given time window;

[0159] The interference pattern acquisition module is used to calculate the interference pattern of each sub-array after beamforming;

[0160] A linear phase interval acquisition module is used to calculate the linear phase interval of each interferogram between sub-arrays;

[0161] The amplitude value acquisition module is used to perform weighted averaging on the interference pattern using the amplitude information in the water body map, and find the corresponding amplitude value in the water body according to each index value;

[0162] A phase difference acquisition module is used to obtain a phase difference according to the interference pattern after weighted smoothing;

[0163] Get the horizontal distance and depth module to calculate the horizontal distance and depth of each ping.

[0164] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application is described in detail with reference to the embodiments, a person skilled in the art should understand that any modification or equivalent replacement of the technical solution of the present application does not depart from the spirit and scope of the technical solution of the present application and should be included in the scope of the claims of the present application.

Claims

1. An ultra-wide coverage method for deep-water near-bottom multi-beam sonar, comprising: Step 1: low-pass filter the real and imaginary raw data collected by the receiving transducer to obtain the analytical signal; Step 2: Perform near-field focusing on the analytical signal to compensate for the phase error when the sound wave diffuses as a spherical wave; Step 3: Perform windowed conventional beamforming on all array elements on the analytical signal after near-field focusing to obtain a water body image; Step 4: Divide all array elements into P spatially overlapping sub-arrays, with a spacing of half a wavelength between each sub-array, and perform windowed conventional beamforming on each sub-array; Step 5: Construct the amplitude-phase method time window; Step 6: In a given time window, use the weighted time average method within the set beam opening angle to obtain the TOA value under the amplitude method; Step 7: Calculate the interference pattern after beamforming of each sub-array; Step 8: Calculate the linear phase interval of each inter-subarray interference pattern; Step 9: Use the amplitude information in the water body map to perform weighted averaging on the interference pattern, and find the corresponding amplitude value in the water body according to each index value; Step 10: Obtain the phase difference according to the weighted smoothed interference pattern; Step 11: Calculate the horizontal distance and depth of each ping; calculate the central beam water depth and input it into the next ping, and repeat the above operation in a loop.

2. The ultra-wide coverage method for deep-water near-bottom multi-beam sonar according to claim 1, characterized in that: The step 2 comprises: The analytical signal expression after near-field focusing is: S Fresnel =S filter *exp(-jΔφ Fresnel ) Among them, S filter is the analytical signal after low-pass filtering; S Fresnel is the analytical signal after near-field focusing; Δφ Fresnel is the phase compensation factor for near-field focusing: Where r is the distance from the center element to the seabed; Δx n is the offset between other elements and the central element on the receiving array; λ is the signal wavelength.

3. The ultra-wide coverage method for deep-water near-bottom multi-beam sonar according to claim 2, characterized in that: The step 3 comprises: Beamforming is performed on the analytical signal after near-field focusing, and the side lobes are suppressed by adding a Hamming window. The beam pointing angle is set to 0°, and the expression of all array elements after beamforming is obtained as follows: B a =∑S Fresnel *exp(-j2π(n-1)dsin(θ0) / λ).*hamming(M),n=0,1,2,...N-1 Where N is the number of array elements; d is the array element spacing; θ0 is the beamforming pointing angle; M is the number of sampling points; B a The full array beam output data of all array elements; E a is a water body diagram; (·). The subscript operator in the middle represents the multiplication of each element of the vector separately; hamming(M) is the Hamming window, expressed as: The water body map is obtained by beamforming all array elements, and its expression is: E a =|B a | 2 The step 4 comprises: Divide all array elements into P equally spaced subarrays, with each subarray spaced at λ / 2, and obtain the beamforming data B for each subarray pi for:

4. The ultra-wide coverage method for deep-water near-bottom multi-beam sonar according to claim 3, characterized in that: The step 5 comprises: The time window expression of the amplitude-phase method is: W(k)=T+2H ref (k) / c*tan(|A0(k)|+α) / cos(|A0(k)|-α),k=1,2,3,...K Where W(k) represents the time window of the kth ping; T is the signal pulse width; H ref (k) is the central beam water depth of the kth ping iteration; c is the sound speed; K is the number of pings; α is the time window margin; A0(k) is the kth ping beam angle.

5. The ultra-wide coverage method for deep-water near-bottom multi-beam sonar according to claim 4, characterized in that: The step 6 comprises: TOA value under amplitude method a The expression is: Among them, E a,t is the water body energy range within the time window, t min is the minimum value of the time window W(k), t max is the maximum value of the time window W(k), and t is the sampling point value in the time window.

6. The ultra-wide coverage method for deep-water near-bottom multi-beam sonar according to claim 5, characterized in that: The step 7 comprises: Interference pattern P after beamforming of each subarray ij for: Among them, B pi is the beam output data of the i-th subarray, (.) H is the complex conjugate operator.

7. The ultra-wide coverage method for deep-water near-bottom multi-beam sonar according to claim 6, characterized in that: The step 9 comprises: Interference pattern after amplitude weighted smoothing The expression is: in, represents the linear phase interval of the interference pattern between each sub-array; w a It is the amplitude information of the corresponding index value in the water body map.

8. The ultra-wide coverage method for deep-water near-bottom multi-beam sonar according to claim 7, characterized in that: The step 10 comprises: According to the interference pattern after weighted smoothing Get the phase difference The quadratic fitting coefficients a0, a1, and a2 are calculated based on the smoothed phase difference, where a0 is the quadratic term coefficient, a1 is the linear term coefficient, and a2 is the constant term; the TOA value of each subarray under the phase method is obtained. Pij : Compare the two roots obtained from the quadratic equation and select the real part of the root closest to the time window as the result; when considering P subarrays, P-1 different TOA values ​​need to be calculated, and the average value of the P-1 TOA values ​​is calculated as the final total TOA value under the phase method. p , whose expression is:

9. The ultra-wide coverage method for deep-water near-bottom multi-beam sonar according to claim 8, characterized in that: The step 11 comprises: The horizontal distance X(n) and depth H(n) of each ping are: Where A0(n) represents the angle of the nth beam in 1 ping; R represents the number of waves; The boundary between the amplitude method and the phase method is:

10. An ultra-wide coverage system for deep-water near-bottom multi-beam sonar, implemented based on any of the methods described in claims 1-9, characterized in that: The system comprises: The analytical signal acquisition module is used to perform low-pass filtering on the real and imaginary original data collected by the receiving transducer to obtain the analytical signal; The near-field focusing module is used to perform near-field focusing on the analytical signal to compensate for the phase error when the sound wave diffuses as a spherical wave; A water body image acquisition module is used to perform windowed conventional beamforming on all array elements on the analytical signal after near-field focusing to obtain a water body image; A subarray division module is used to divide all array elements into P subarrays that overlap in space, with a spacing of half a wavelength between each subarray, and perform windowed conventional beamforming on each subarray; Construct a time window module, which is used to construct the amplitude-phase method time window; A module for obtaining the TOA value under the amplitude method is used to obtain the TOA value under the amplitude method by using a weighted time average method within a set beam opening angle in a given time window; The interference pattern acquisition module is used to calculate the interference pattern of each sub-array after beamforming; A linear phase interval acquisition module is used to calculate the linear phase interval of each interferogram between sub-arrays; The amplitude value acquisition module is used to perform weighted averaging on the interference pattern using the amplitude information in the water body map, and find the corresponding amplitude value in the water body according to each index value; A phase difference acquisition module is used to obtain a phase difference according to the weighted smoothed interference pattern; and Get the horizontal distance and depth module to calculate the horizontal distance and depth of each ping.

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