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

Abstract

The present application provides an ultra-wide coverage method and system for a deep-water near-bottom multi-beam sonar. The method includes: performing low-pass filtering on the data collected by the receiving transducer to obtain an analytical signal; performing near-field focusing on the analytical signal; performing windowed conventional beamforming on all array elements to obtain a water body image; dividing the array elements into P sub-arrays that overlap spatially, and performing windowed conventional beamforming on each sub-array respectively; constructing an amplitude-phase method time window; using a weighted time averaging method to obtain the TOA value under the amplitude method; calculating the interferogram after beamforming for each sub-array; calculating the linear phase interval of the interferogram between each sub-array; performing weighted averaging on the interferogram to find the corresponding amplitude value in the water body; obtaining the phase difference according to the weighted and smoothed interferogram; calculating the horizontal distance and depth for each ping, and repeatedly executing the above operations. The advantages of the present application are: it can ensure ultra-wide coverage while adapting to more complex terrains.

Description

Technical Field

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

[0002] Deep-water near-bottom multi-beam sonars can operate in deep waters of kilometers or even tens of thousands of meters, and achieve an ultra-wide water depth coverage of 5 - 5.5 times at heights ranging from 20 to 200 meters above the seabed. Currently, most deep-water near-bottom multi-beam sonars use the amplitude-phase joint detection method for seabed mapping. Since the seabed backscattering contribution is large and the echo energy is strong in the area directly below, the amplitude method is generally used in the area directly below; while for the seabed 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 a weighted time averaging 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 topography is relatively flat. However, when the seabed topography is rough, the effect of this method is often not satisfactory. This is because the phase method only uses two subarrays. When the seabed topography becomes complex, the overall variance of the data is large, and using two subarrays cannot reduce the variance through averaging or other means. At the same time, the time window of the amplitude-phase joint detection method is related to the water depth of the central beam. When facing complex terrain, the water depth of the central beam varies significantly between adjacent pings. If the water depth of the central beam is not accurately calculated, a large number of sounding 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 complex seabed terrain conditions.

[0005] To achieve the above purpose, this application proposes an ultra-wide coverage method for a deep-water near-bottom multi-beam sonar, including:

[0006] Step 1: Perform low-pass filtering on the real and imaginary original data collected by the receiving transducer to obtain an analytic signal;

[0007] Step 2: Perform near-field focusing on the analytic 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 of the analytic signal after near-field focusing to obtain a water body image;

[0009] Step 4: Divide all array elements into P subarrays that overlap in space, with each subarray spacing being half a wavelength, and perform windowed conventional beamforming on each subarray respectively;

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

[0011] Step 6: Under the given time window, adopt the weighted time averaging 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 for each subarray;

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

[0014] Step 12: 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 15: Obtain the phase difference according to the weighted and smoothed interference pattern;

[0016] Step 11: Calculate the horizontal distance and depth for each ping; Calculate the water depth of the central beam and input it to the next ping, and loop to execute the above operations.

[0017] As an improvement of the above method, the said Step 2 includes:

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

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

[0020] Wherein, 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] Wherein, r is the distance from the central array element to the seabed; Δx n is the offset between other array elements on the receiving array and the central array element; λ is the signal wavelength.

[0023] As an improvement of the above method, the said Step 3 includes:

[0024] Perform beamforming on the analytical signal after near-field focusing, suppress the sidelobes by adding a Hamming window, and set the beam pointing angle to 0°, and the expression after beamforming for all array elements is:

[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 element spacing; θ0 is the beamforming steering angle; M is the number of sampling points; B a is the full array beam output data of all array element outputs; E a is the water body map; the dot operator in (·) means that each element of the vector is multiplied separately;

[0027] hamming(M) is the Hamming window, and the expression is:

[0028]

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

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

[0031] The said step 4 includes:

[0032] Divide all array elements into P sub - arrays with equal intervals, and the interval of each sub - array is λ / 2, and the beamforming data B of each sub - array pi is:

[0033]

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

[0035] The amplitude - phase method time window expression 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 k - th ping; T is the signal pulse width; H ref (k) is the central beam water depth of the k - th ping iteration; c is the sound speed; K is the number of pings; α is the time window margin; A0(k) is the beam angle of the k - th ping.

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

[0039] The TOA value TOA a under the amplitude method is expressed as:

[0040]

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

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

[0043] The interference pattern P after beamforming of each subarray ij is:

[0044]

[0045] Among them, B pi is the beam output data of the i-th subarray, and (.) 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] Among them, represents the linear phase interval of the interference pattern between each subarray; w a 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 obtain the phase difference

[0052]

[0053] Calculate the quadratic fitting coefficients a0, a1, a2 according to the smoothed phase difference, a0 is the quadratic term coefficient, a1 is the linear term coefficient, and a2 is the constant term; obtain the TOA value TOA of each subarray under the phase method 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 sub-arrays, it is necessary to calculate P - 1 different TOA values, and calculate the average value of these P - 1 TOAs as the final total TOA value TOA under the phase method p , and its 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 one ping; R represents the number of wave numbers;

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

[0062]

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

[0064] An acquisition of analytic signal module, which is used to perform low-pass filtering on the real and imaginary part raw data collected by the receiving transducer to obtain an analytic signal;

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

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

[0067] A sub-array division module, which is used to 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 respectively;

[0068] A construction of time window module, which is used to construct an amplitude-phase method time window;

[0069] An acquisition of TOA value under amplitude method module, which is used to obtain the TOA value under the amplitude method by using a weighted time averaging method within a given time window and within a set beam opening angle;

[0070] An acquisition of interferogram module, which is used to calculate the interferogram after beamforming of each sub-array;

[0071] A linear phase interval obtaining module, which is used to calculate the linear phase interval of each sub-array interference pattern;

[0072] An amplitude value obtaining module, which is used to perform weighted averaging on the interference pattern by 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 obtaining module, which is used to obtain the phase difference according to the interference pattern after weighted smoothing;

[0074] A horizontal distance and depth obtaining module, which is used to calculate the horizontal distance and depth of each ping.

[0075] Compared with the prior art, the advantages of the present application are as follows:

[0076] The present application accurately calculates the water depth of the central beam through the iterative method of each ping, and uses the amplitude information in the water body image after beamforming to perform weighted smoothing on the interference pattern. By adopting the method proposed in the present application, it is possible to ensure ultra-wide coverage while adapting to more complex terrains. Description of the Drawings

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

[0078] Figure 2 Shown is a schematic diagram of sub-array division;

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

[0080] Figure 4 Shown is after the method of the present invention and Figure 3 The fusion result map with the water body map in;

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

[0082] Figure 6 Shown is the fusion result map with the water body map after adopting the weighted time averaging - split sub-array method under a rugged seabed in a certain sea area;

[0083] Figure 7 Shown is the fusion result map with the water body map after adopting the method of the present invention under a rugged seabed in a certain sea area. Detailed Embodiments

[0084] The technical solution of the present application will be described in detail below with reference to the 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, to reduce the sidelobe in this way and improve the accuracy of the subsequent amplitude method; the second is to divide multiple sub-arrays, and reduce the variance of the data by averaging multiple sub-arrays to improve the accuracy of the phase method; the third is to window and smooth the complex interferogram between sub-arrays. By smoothing the phase difference, the bathymetric accuracy can also be improved to a certain extent. For the third method, using window smoothing does not utilize the amplitude information in the data. Since the window parameters are fixed, the multi-beam sonar will not obtain the optimal result when working under various different seabed topographies. At the same time, it is necessary to accurately calculate the water depth of the central beam so that the time window can be iteratively adjusted according to different water depths of the central beam.

[0086] The present invention discloses an ultra-wide coverage method and system for a deep-water near-bottom multi-beam sonar, accurately calculates the water depth of the central beam by means of each ping iteration, and uses the amplitude information in the water body image after beamforming to weight and smooth the interferogram. Compared with the existing methods, the method proposed by the present invention can adapt to more complex terrains while ensuring ultra-wide coverage.

[0087] Embodiment 1

[0088] As Figure 1 shown, an ultra-wide coverage method for a deep-water near-bottom multi-beam sonar provided by the present invention includes:

[0089] Step 1: Receive the real part and imaginary part of the original 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] where data_I and data_Q are the real part and imaginary part signals of the original data.

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

[0095] Due to the different heights of the deep - water near - bottom multibeam sonar from the seabed, the distance each ping reaches the seabed is also different. When the sonar operates in the near - field, since the sound wave propagates in a spherical - wave form, there are differences in the echo signal delays received by each element on the receiving array. Taking the central element of the receiving array as a reference (which can be considered to have the shortest echo delay), the distance from the central element to the seabed is r, and the offset between other elements on the receiving array and the central element is denoted as Δx n , so the path - difference of different elements relative to the central element to the seabed is obtained as:

[0096]

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

[0098]

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

[0100]

[0101] The expression of the analytic signal after near - field focusing is:

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

[0103] where S filter is the analytic signal after low - pass filtering, and S Fresnel is the analytic signal after near - field focusing.

[0104] Step 3: Perform windowed conventional beamforming on all elements of the analytic signal after near - field focusing to obtain the water - body image.

[0105] Perform beamforming on the analytic signal after near - field focusing and suppress the sidelobes to a certain extent by applying a Hamming window. Assuming the beam - pointing angle is 0°, the expression after beamforming for all elements is:

[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 elements, d is the element spacing, λ is the signal wavelength, θ0 is the beam - forming pointing angle, M is the number of sampling points, B a is the full - array beam output data output by all elements, and E a is the water - body map.

[0108] The Hamming window expression is as follows:

[0109]

[0110] The water body map is obtained by beamforming of 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. The spacing between each sub-array is half a wavelength, and windowed conventional beamforming is performed on each sub-array separately. If the value of P is too small, the ideal effect cannot be achieved; if the value is too large, the computational complexity will increase. Preferably, P is 6.

[0113] As Figure 2 shown, divide all array elements into P equally spaced sub-arrays, with the interval between each sub-array being λ / 2, and obtain the beamforming data of each sub-array. Assuming there are N array elements, the beam data expression of each sub-array is:

[0114]

[0115] Among them, the punctuation operator in (·) means that each element of the vector is multiplied separately.

[0116] Step 5: Construct an amplitude-phase method time window, and 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] Among them, W(k) represents the time window of the k-th ping; T is the signal pulse width, H ref (k) is the central beam water depth 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 shown, the prior central beam water depth needs to be input for the first ping, 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: Under the given time window, use the weighted time averaging method within a certain beam opening angle to obtain the TOA value (time of arrival of the signal) TOA under the amplitude method a .

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

[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 within the time window.

[0123] Step 7: Calculate the interferogram after beamforming for each subarray, 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 the interferogram between each subarray, record the starting index of the linear phase as s idx , and record the ending index as e idx , and the expression of the linear phase interval of the interferogram between each subarray is:

[0127]

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

[0129]

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

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

[0132] Step 10: Obtain the phase difference according to the interferogram after weighted smoothing, and its expression is:

[0133]

[0134] Calculate the quadratic fitting coefficients a0, a1, a2 according to the smoothed phase difference:

[0135] φ(t) = a0t 2 + a1t + a2

[0136] Obtain the TOA value TOA of each sub - array under the phase method Pij , and its expression is:

[0137]

[0138] 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 sub - arrays, P - 1 different TOA values need to be calculated, and the average value is calculated based on these P - 1 TOAs as the final total TOA value TOA under the phase method p , and its expression is:

[0139]

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

[0141]

[0142] where A0(n) represents the angle of the nth beam in one ping

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

[0144]

[0145] At the same time, input the water depth H ref = H(R / 2) of the central beam calculated into the next ping, and repeat the above operations

[0146] By iteratively and accurately calculating the water depth of the central beam of each ping and using the amplitude information in the water body map for interferogram weighted smoothing, it can ensure the ultra - wide coverage of the deep - water near - bottom multi - beam sonar while adapting to more complex terrains

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

[0148] As Figure 3 shown, it can be seen from the water body diagram that it is a flat seabed. Through the method of the present invention, Figure 4 obtained, for the fusion of the bottom finding diagram and the water body diagram, the water depth H of the central beam ref is approximately 46 meters. According to Figure 4 the marked farthest horizontal distances at both ends are -112 meters and 133 meters respectively, the maximum coverage width X of this sonar can be obtained max is 245 meters, so the coverage range expression is:

[0149]

[0150] By calculation, Q is 5.3, verifying the effectiveness of the ultra-wide coverage of the method of the present invention. As Figure 5 shown, it can be seen from the water body diagram that it is a rugged seabed, and it can be considered that this is a complex seabed terrain at this time. Through Figure 6 and Figure 7 comparison, it can be seen that compared with the traditional weighted time averaging - 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 multi-subarrays and using the amplitude information in the water body diagram for weighted smoothing, comparing Figure 6 , Figure 7 the red marked parts at both ends, Figure 6 the data points in Figure 7 become discrete, while

[0151] Embodiment 2

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

[0153] An acquisition and analysis signal module, which is used to perform low-pass filtering on the real and imaginary original data collected by the receiving transducer to obtain an analysis signal;

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

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

[0156] The sub - array division module is used to divide all array elements into P sub - arrays that overlap spatially. The spacing between each sub - array is half - wavelength, and windowed conventional beamforming is performed on each sub - array respectively.

[0157] The time - window construction module is used to construct an amplitude - phase method time window.

[0158] The TOA value acquisition module 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 within a given time window.

[0159] The interferogram acquisition module is used to calculate the interferogram after beamforming of each sub - array.

[0160] The linear - phase interval acquisition module is used to calculate the linear - phase interval of the interferogram between each sub - array.

[0161] The amplitude - value acquisition module is used to perform weighted averaging on the interferogram 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] The phase - difference acquisition module is used to obtain the phase difference according to the weighted - smoothed interferogram.

[0163] The horizontal - distance and depth acquisition module is used 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 solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present application does not depart from the spirit and scope of the technical solutions of the present application, and they should all be covered within 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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