Sonar image beam sharpening method, system and device based on phase difference data

Abstract

The invention relates to the technical field of underwater surveying and mapping, and discloses a sonar image beam sharpening method, system and device based on phase difference data, which solves the practical problem of improving beam angle resolution. The technical solution thereof comprises the following steps: S1, dividing a transducer receiving linear array into a left subarray and a right subarray, and performing beamforming processing on the left subarray and the right subarray respectively to obtain a left subarray beamforming result and a right subarray beamforming result; S2a, conjugate multiplying the left subarray beamforming result and the right subarray beamforming result to obtain a phase difference time series, calculating an amplitude weighting coefficient according to the phase difference time series, and limiting the amplitude weighting coefficient; S2b, adding the left subarray beamforming result and the right subarray beamforming result to obtain an amplitude time series; S3, multiplying the amplitude time series and the amplitude weighting coefficient to obtain sharpened beamforming amplitude data, which can improve the beam angle spatial resolution.

Description

Technical Field

[0001] The present invention relates to the field of underwater surveying and mapping technology, and more specifically, to a sonar image beam sharpening method, system and device based on phase difference data. Background Art

[0002] Sonar beamforming is a signal processing technology used in sonar systems. It focuses the sound wave energy in a specific direction by controlling the phase and amplitude of multi-channel signals to achieve higher resolution and signal-to-noise ratio. This technology is widely used in underwater detection, acoustic imaging, and positioning and tracking targets such as submarines, schools of fish or other underwater objects.

[0003] The acoustic wet end of a multibeam bathymetric sonar mainly includes a transmitting transducer and a receiving transducer array. According to the linear array beamforming theory, the larger the array aperture, the smaller the beam width, and the higher the angular resolution of the image obtained. For a multibeam bathymetric sonar, the higher the beam resolution, the narrower the echo interval at the bottom of the sonar image, which is conducive to the interpretation of the bottom interval.

[0004] In order to improve the beam angle resolution, most domestic and foreign multi-beam depth sounding sonar equipment manufacturers configure dozens or even hundreds of channels. Taking the half-wavelength array as an example, according to the array beam width calculation formula, if you want to get a beam angle resolution of 0.5 degrees, you need 192 channels. The more channels there are, the longer the transducer array is, which makes the equipment larger and heavier. In addition, the complexity of the entire sonar system increases, and the power consumption also increases accordingly.

[0005] In order to obtain higher beam angle resolution, in addition to increasing the number of channels, high-resolution beamforming technology can also be used. Commonly used high-resolution beamforming technologies include MVDR, MUSIC and other algorithms. However, such algorithms are very computationally intensive, difficult to implement in algorithm engineering, and have few successful application cases.

[0006] In summary, according to array theory, in order to improve the beam angle resolution and shorten the bottom echo interval interpretation, the most direct way is to increase the number of transducer array elements. If the number of transducer channels does not increase, the use of adaptive beamforming algorithms can also improve the beam angle spatial resolution. However, these two methods undoubtedly bring huge cost pressure to the multi-beam sonar hardware and software systems: increasing the number of channels will increase the hardware cost, and the entire system will become more complex; using adaptive beamforming algorithms, the amount of calculation increases dramatically, increasing the burden on the system software, which is theoretically feasible, but not easy to implement in engineering. Summary of the invention

[0007] The purpose of the present invention is to provide a sonar image beam sharpening method, system and device based on phase difference data, which can improve the spatial resolution of the beam angle, have a simple calculation process, a small amount of calculation, and are easy to implement in engineering without increasing the system software cost.

[0008] The above technical objective of the present invention is achieved through the following technical solution: a sonar image beam sharpening method based on phase difference data comprises the following steps:

[0009] S1, dividing the transducer receiving linear array into a left sub-array and a right sub-array, and performing beamforming processing on the left sub-array and the right sub-array respectively to obtain the left sub-array beamforming result and the right sub-array beamforming result, and then executing S2a and S2b respectively;

[0010] S2a, conjugate multiplying the left sub-array beamforming result and the right sub-array beamforming result to obtain a phase difference time series, calculating an amplitude weighting coefficient according to the phase difference time series, and limiting the amplitude weighting coefficient;

[0011] S2b, adding the beamforming result of the left sub-array and the beamforming result of the right sub-array to obtain an amplitude time series;

[0012] S3. Multiply the amplitude time series and the amplitude weighting coefficient to obtain the sharpened beamforming amplitude data.

[0013] As a preferred technical solution of the present invention, S1, it is assumed that the transducer receiving linear array has Array element, The signal of an array element is , then the beamforming output result is It can be expressed as: ;in is the amplitude weighting coefficient of each array element, is the time delay of each channel, It is the delayed signal;

[0014] The beamforming result of the left subarray is expressed as , the beamforming result of the right subarray is expressed as ,in, , .

[0015] As a preferred technical solution of the present invention, in S2a, the phase difference time series is expressed as: ,in is the phase function, To take the conjugate function;

[0016] The amplitude weighting coefficient is expressed as: ,in, is the collection time point, is the number of smoothing points near the sampling point;

[0017] The amplitude weighting coefficient is restricted, expressed as:

[0018] ,in, is a constant with a value range of .

[0019] As a preferred technical solution of the present invention, in S2b, the amplitude time series is expressed as: ;in is the amplitude function.

[0020] As a preferred technical solution of the present invention, in S3, the beamforming amplitude data after sharpening is expressed as:

[0021] .

[0022] Sonar image beam sharpening system based on phase difference data, including:

[0023] An array division module is used to divide the transducer receiving linear array into a left sub-array and a right sub-array, and perform beamforming processing on the left sub-array and the right sub-array respectively to obtain a left sub-array beamforming result and a right sub-array beamforming result;

[0024] An amplitude weighting coefficient calculation module is used to conjugate multiply the left subarray beamforming result and the right subarray beamforming result to obtain a phase difference time series, calculate the amplitude weighting coefficient according to the phase difference time series, and limit the amplitude weighting coefficient;

[0025] An amplitude data calculation module is used to add the left sub-array beamforming result and the right sub-array beamforming result to obtain an amplitude time series;

[0026] The sharpening amplitude calculation module is used to multiply the amplitude time series and the amplitude weighting coefficient to obtain the beamforming amplitude data after sharpening.

[0027] A sonar image beam sharpening device based on phase difference data comprises: a processor and a memory, wherein the memory stores a computer program executable by the processor, and the processor implements the above method when executing the computer program.

[0028] In summary, the present invention has the following beneficial effects: it can improve the spatial resolution of beam angles, and for multi-beam bathymetric sonar, it can greatly shorten the width of the water bottom echo interval of the multi-beam bathymetric sonar, thereby facilitating water depth measurement and improving the accuracy of water depth measurement. Compared with the method of increasing the number of transducer array elements and using an adaptive beamforming algorithm, the present invention does not need to increase the number of receiving transducer channels, does not increase the hardware cost of the multi-beam bathymetric sonar system, has a simple calculation process, a small amount of calculation, is easy to implement in engineering, and does not increase the system software cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the method of the present invention;

[0030] Figure 2 is the original phase data diagram of the present invention;

[0031] Figure 3 The present invention Time series plots;

[0032] Figure 4 It is a time series diagram of the original beam amplitude of a single beam of the present invention;

[0033] Figure 5 is a time series diagram of beam amplitude after single beam processing of the present invention;

[0034] Figure 6 is the beamforming echo raw sonar image of the present invention;

[0035] Figure 7 This is the sonar image after beamforming echo weighting and sharpening of the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0037] According to the beam characteristics, the spatial resolution of the multi-beam transducer array beam depends on the number of array element channels. The more channels there are, the higher the spatial resolution. In addition, the effective beam widths of different beam pointing angles of the same transducer receiving array are also different, that is, the spatial resolution of the beams in different directions is also different. The middle beam has the highest beam resolution, and the edge beam has a low spatial resolution. This phenomenon is called beam broadening. For multi-beam bathymetric sonar beams, the smaller the beam resolution, the smaller the beam footprint, and the effective range of the bottom echo becomes narrower, and the water depth measurement accuracy increases.

[0038] Therefore, the present invention provides a sonar image beam sharpening method based on phase difference data, which is used to improve the spatial resolution of the edge beam angle. Figure 1 As shown, the specific steps include:

[0039] S1, dividing the transducer receiving linear array into a left sub-array and a right sub-array, and performing beamforming processing on the left sub-array and the right sub-array respectively to obtain the left sub-array beamforming result and the right sub-array beamforming result, and then executing S2a and S2b respectively;

[0040] The specific content is: Assume that the transducer receiving linear array has Array element, The signal of an array element is , then the beamforming output result is It can be expressed as: ;in is the amplitude weighting coefficient of each array element, is the time delay of each channel, It is the delayed signal;

[0041] The beamforming result of the left subarray is expressed as , the beamforming result of the right subarray is expressed as ,in, , .

[0042] The core idea of ​​beamforming is to use array antennas or transducer arrays to control the phase difference or time delay between signals received by different sensors so that sound waves are superimposed in a specific direction, thereby enhancing the signal strength in that direction while suppressing interference in other directions.

[0043] S2a, conjugate multiply the left sub-array beamforming result and the right sub-array beamforming result to obtain a phase difference time series, which is expressed as: ,in is the phase function, To take the conjugate function;

[0044] According to the phase difference time series, the amplitude weighting coefficient is designed and calculated. In the absence of echo, the phase difference between the left and right sub-arrays is randomly distributed between positive and negative, and the statistical mean is 0. When there is echo, the phase difference time series can be approximated as a straight line crossing the zero axis under ideal conditions. For details, see Figure 2 As shown. Based on this feature, we calculate the average phase difference near the sampling point. Obviously, when there is no echo, the average phase difference is small and close to 0. When there is a bottom echo, the closer to the center of the echo, the smaller the average phase difference is, and the farther away from the center, the larger the absolute value is.

[0045] Therefore, the amplitude weighting coefficient design is expressed as: ,in, is the collection time point, is the number of smoothing points near the sampling point;

[0046] The amplitude weighting coefficient is restricted, expressed as:

[0047] ,in, is a constant with a value range of , the detailed time series is as follows Figure 3 As shown, the red line indicates the selected value.

[0048] S2b, adding the beamforming result of the left sub-array and the beamforming result of the right sub-array to obtain an amplitude time series;

[0049] The amplitude time series is expressed as: ;in is the amplitude function.

[0050] S3. Multiply the amplitude time series and the amplitude weighting coefficient to obtain the sharpened beamforming amplitude data. The sharpened beamforming amplitude data is expressed as: . Figure 4 is the original beam amplitude time series of a single beam, Figure 5 It is the beam amplitude time series after single beam processing. By comparison, it is found that the beam amplitude width after processing is smaller than the unprocessed beam amplitude data, which reduces the beam footprint.

[0051] Corresponding to the above method, the present invention also provides a sonar image beam sharpening system based on phase difference data, comprising:

[0052] An array division module is used to divide the transducer receiving linear array into a left sub-array and a right sub-array, and perform beamforming processing on the left sub-array and the right sub-array respectively to obtain a left sub-array beamforming result and a right sub-array beamforming result;

[0053] An amplitude weighting coefficient calculation module is used to conjugate multiply the left subarray beamforming result and the right subarray beamforming result to obtain a phase difference time series, calculate the amplitude weighting coefficient according to the phase difference time series, and limit the amplitude weighting coefficient;

[0054] An amplitude data calculation module is used to add the left sub-array beamforming result and the right sub-array beamforming result to obtain an amplitude time series;

[0055] The sharpening amplitude calculation module is used to multiply the amplitude time series and the amplitude weighting coefficient to obtain the beamforming amplitude data after sharpening.

[0056] Corresponding to the above method and system, the present invention also provides a sonar image beam sharpening device based on phase difference data, including: a processor and a memory, the memory stores a computer program executable by the processor, and the processor implements the above method when executing the computer program.

[0057] As an embodiment of the present invention, conventional beam forming and beam sharpening processing is performed on the data collected by the actual acoustic device. The result is shown below: Figure 6 Output results of raw beamforming amplitudes for all beams. Conventional sonar image processing operations are to perform beamforming on all array channel data and obtain amplitude values.

[0058] Figure 7 The output result of amplitude-weighted sharpening of all beam raw sonar data. The horizontal axis in the figure represents the sampling time point, and the vertical axis represents different beam opening angles. Taking the beam opening angle of 30 degrees as an example, after being processed by the method of the present invention, the beamforming amplitude output bottom echo highlight area is significantly narrower than before processing. The overall sonar image achieves a sharpening effect. This will be of great help to the subsequent bottom echo tracking and bottom detection accuracy.

[0059] The technical advantage of the present invention is that it can improve the spatial resolution of beam angles, and for multi-beam bathymetric sonar, it can greatly shorten the width of the bottom echo interval of the multi-beam bathymetric sonar, thereby facilitating water depth measurement and improving the accuracy of water depth measurement. Compared with the method of increasing the number of transducer array elements and using an adaptive beamforming algorithm, the present invention does not need to increase the number of receiving transducer channels, does not increase the hardware cost of the multi-beam bathymetric sonar system, has a simple calculation process, a small amount of calculation, is easy to implement in engineering, and does not increase the system software cost.

[0060] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A sonar image beam sharpening method based on phase difference data, characterized by: The steps include: S1. Divide the transducer receiving linear array into a left sub-array and a right sub-array, and perform beamforming processing on the left sub-array and the right sub-array respectively to obtain the left sub-array beamforming result and the right sub-array beamforming result. Assume that the transducer receiving linear array has Array element, The signal of an array element is , then the beamforming output result is It can be expressed as: ;in is the amplitude weighting coefficient of each array element, is the time delay of each channel, is the delayed signal; the beamforming result of the left subarray is expressed as , the beamforming result of the right subarray is expressed as , , ; Then execute S2a and S2b respectively; S2a, conjugate multiply the left sub-array beamforming result and the right sub-array beamforming result to obtain a phase difference time series, calculate the amplitude weighting coefficient according to the phase difference time series, and restrict the amplitude weighting coefficient; the phase difference time series is expressed as: ,in is the phase function, is the conjugate function; the amplitude weighting coefficient is expressed as: ,in, is the collection time point, is the number of smoothing near the sampling point; the amplitude weighting coefficient is restricted, expressed as: ,in, is a constant with a value range of ; S2b, adding the beamforming result of the left sub-array and the beamforming result of the right sub-array to obtain an amplitude time series; S3. Multiply the amplitude time series and the amplitude weighting coefficient to obtain the sharpened beamforming amplitude data.

2. The sonar image beam sharpening method based on phase difference data according to claim 1 is characterized in that: In S2b, the amplitude time series is expressed as: ;in is the amplitude function.

3. The sonar image beam sharpening method based on phase difference data according to claim 2 is characterized in that: in S3, the beamforming amplitude data after sharpening is expressed as: 。 4. A sonar image beam sharpening system based on phase difference data, characterized by: include: The array division module is used to divide the transducer receiving linear array into a left sub-array and a right sub-array, and perform beamforming processing on the left sub-array and the right sub-array respectively to obtain the left sub-array beamforming result and the right sub-array beamforming result; and the transducer receiving linear array is assumed to have Array element, The signal of an array element is , then the beamforming output result is It can be expressed as: ;in is the amplitude weighting coefficient of each array element, is the time delay of each channel, is the delayed signal; the beamforming result of the left subarray is expressed as , the beamforming result of the right subarray is expressed as , , ; The amplitude weighting coefficient calculation module is used to conjugate multiply the left sub-array beamforming result and the right sub-array beamforming result to obtain a phase difference time series, calculate the amplitude weighting coefficient according to the phase difference time series, and restrict the amplitude weighting coefficient; the phase difference time series is expressed as: ,in is the phase function, is the conjugate function; the amplitude weighting coefficient is expressed as: ,in, is the collection time point, is the number of smoothing near the sampling point; the amplitude weighting coefficient is restricted, expressed as: ,in, is a constant with a value range of ; An amplitude data calculation module is used to add the left sub-array beamforming result and the right sub-array beamforming result to obtain an amplitude time series; The sharpening amplitude calculation module is used to multiply the amplitude time series and the amplitude weighting coefficient to obtain the beamforming amplitude data after sharpening.

5. A sonar image beam sharpening device based on phase difference data, characterized in that: include: A processor and a memory, wherein the memory stores a computer program executable by the processor, and when the processor executes the computer program, the method according to any one of claims 1 to 3 is implemented.

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