A wide-angle scanning imaging device, method and system

Abstract

The present invention discloses a wide-angle scanning imaging device, method and system, comprising a sonar probe and a device body; the sonar probe comprises an acoustic array and a transceiver processing module; the acoustic array comprises a transmitting array and a receiving array; the transmitting array comprises a group of transmitting transducers, the maximum response axis of the transmitting transducers is distributed in the vertical direction according to a preset inclination angle, and multiple transmitting beams of the transmitting transducers form a wide-angle coverage in the vertical direction; the receiving array is distinguished by beamforming in the horizontal direction, and the vertical azimuth of the echo is estimated by the phase difference output by the double arrays; the acoustic array rotates along the central axis of the device body; the transmitting array transmits broadband orthogonal pulses according to a preset period, and the receiving array receives the echo signal, and after being processed by the transceiver processing module according to the central frequency of the transmitting pulse of the transmitting array, the underwater target imaging result is obtained. The present invention reduces the influence of underwater multipath interference and the like on phase estimation and improves the 3D imaging quality.

Description

Technical Field

[0001] The present invention relates to the field of acoustic imaging technology, and in particular to a wide-angle scanning imaging device, method and system. Background Art

[0002] In the field of underwater acoustic imaging, scanning imaging technology combines echo sequences to obtain scanning images through multiple transmission and reception operations. Since scanning imaging reduces the spatial beam side lobes and improves the image distance resolution through pulse compression, high-quality image effects can be obtained in applications. Currently, related side-scan sonar and rotary scanning sonar products have been widely used.

[0003] The patent "360 Degree Imaging Sonar and Method" (US9322915B2) doubles the scanning imaging frame rate through the mechanical rotation of two sets of acoustic transducers in the sonar sound-transmitting cabin. In order to facilitate underwater fish observation, the radiating surface of the sonar transducer is installed at an angle, so that the sonar has the desired downward-tilted beam opening angle. In order to obtain better resolution performance, Tritech's Seaking Hammerhead scanning sonar uses a large-sized dual-frequency sonar probe, and completes scanning imaging by rotating the sonar probe through a mechanical device. Existing scanning imaging sonars usually generate narrow beams in the horizontal direction, and the scanning generation time of an image is equal to the pulse round-trip propagation time multiplied by the number of beams required to cover the imaging viewing angle / travel range. Due to the low speed of sound propagation, this usually takes a long time, so this type of sonar is usually more suitable for imaging static underwater scenes.

[0004] In order to increase the scanning speed, a beam forming method is used to generate multiple receiving beams within a wide horizontal transmission angle, so that the seabed can still be covered at high speeds. For example, the 5900 side scan sonar of Klein Marine Systems also uses multiple echo processes under the condition of a wide horizontal transmission angle to obtain a synthetic aperture processing effect. Patent CN110196428A uses two orthogonal transmitting transducers to obtain a virtual array aperture of about twice the array length.

[0005] In some applications, stereoscopic imaging of underwater scenes is necessary, and underwater 3D scanning imaging results are desired. The prior art provides vertical image information by adding an acoustic array perpendicular to the mechanical scanning direction, such as the BV5000 sonar of Blueview. In some applications (US7215198 B2), vertical scanning is performed by beam-controlled transmission, and the horizontal plane is realized by receiving array beamforming.

[0006] In order to speed up the transmission scanning, the existing technology (CN201410176890.1) realizes pulse orthogonality in different vertical directions through multi-pulse technology or MIMO system. The above 3D imaging methods all require multi-element arrays and multi-channel beam-controlled transmitter equipment in the vertical direction. Another technical approach measures the arrival direction of the echo in the vertical plane by the phase difference of the receiving array. In this way, only two array elements are required for resolution in the vertical direction, which is called interferometric side-scan sonar. However, since phase difference direction finding is susceptible to various decorrelation factors and noise interference, and there is a problem of phase ambiguity, differential interferometry (Vernier method) or multi-phase differential interferometry (MPDI) is generally used to increase the robustness of phase estimation and improve imaging quality, and it has been applied in various depth-measuring side-scan sonar systems.

[0007] In fishing and marine aquaculture, clear and accurate stereoscopic observation of underwater fish schools is required. However, cost constraints make it difficult to put multi-element, high-frame rate imaging systems such as forward-looking sonar and 3D imaging sonar into practical use. Summary of the invention

[0008] In order to solve the above problems, a wide-angle scanning imaging device, method and system are provided to increase the scanning speed, reduce the influence of underwater multipath interference on phase estimation, and improve the 3D imaging quality.

[0009] In a first aspect, the present invention provides a wide-angle scanning imaging device, comprising a sonar probe and a device body;

[0010] The sonar probe includes an acoustic array and a transceiver processing module; the acoustic array includes a transmitting array and a receiving array; the transmitting array includes a group of transmitting transducers, the maximum response axes of the transmitting transducers are distributed in the vertical direction according to a preset inclination angle, and the multiple transmitting beams of the transmitting transducers form a wide angular coverage in the vertical direction;

[0011] The receiving array comprises an upper receiving array and a lower receiving array, and the array elements of the upper linear array and the lower linear array are arranged alternately; the beamforming is used for resolution in the horizontal direction, and the vertical azimuth of the echo is estimated by the phase difference output by the dual arrays;

[0012] The acoustic array rotates along the central axis of the device body; the transmitting array transmits broadband orthogonal pulses according to a preset period, and the receiving array receives the echo signal. After being processed by the transceiver processing module according to the central frequency of the transmitting pulse of the transmitting array, the underwater target imaging result is obtained.

[0013] In some embodiments, the beam package of each transmitting transducer has a horizontal beam width of less than 10° and a vertical beam width of more than 10°; the vertical beam width is several times the horizontal beam width;

[0014] The transmitting transducers are centrally aligned in the horizontal direction and have a preset spacing in the vertical direction for decoupling; each transmitting transducer has a different operating frequency band;

[0015] The transmitting transducer transmits broadband orthogonal pulses according to a preset period, and adopts a frequency-division or code-division orthogonal waveform design.

[0016] In some embodiments, the upper receiving array and the lower receiving array are uniform linear arrays, the array length is L, the number of array elements is greater than L / W, where W is the length of the shortest transmitting array in the horizontal direction; the vertical distance between the linear arrays of the receiving array ranges from 0.5 to 1.5λ c ,λ c is the wavelength corresponding to the median frequency of all transmitted pulses.

[0017] In some embodiments, the plane of the acoustic array forms an angle of 25° to 35° with the horizontal direction.

[0018] In some embodiments, the angular velocity of the rotational motion is equal to the product of the imaging frame rate and the horizontal opening angle of the transmit beam.

[0019] In a second aspect, the present invention further provides a wide-angle scanning imaging method, which is applied to the wide-angle scanning imaging device as described above, and the method comprises the following steps:

[0020] The transmitting array transmits broadband orthogonal pulses according to a preset period;

[0021] The receiving array collects the echo signal, performs orthogonal modulation and down-sampling according to the center frequency of the transmitting array, and obtains a baseband receiving sequence;

[0022] The upper receiving array and the lower receiving array respectively perform broadband digital beamforming processing and matched filtering processing on the baseband receiving sequence to obtain the frequency domain form of the output beam;

[0023] Performing whole array horizontal beamforming processing on the output beam to determine the whole array beam output;

[0024] Performing dual-array phase difference vertical azimuth estimation processing on the output beam to determine the vertical azimuth corresponding to the output beam;

[0025] According to the whole array beam output and the corresponding vertical orientation, the processing results of multiple transducer pulses and the multiple transmission and reception processing results of the scanning process are comprehensively sorted to obtain an image array under a spatial polar coordinate grid;

[0026] The image array is subjected to noise suppression, coordinate transformation, and image optimization processing to obtain underwater target imaging results.

[0027] In some implementations, the baseband receive sequence is

[0028] x n,m (t n ), t n =0,1,2,...,TN; n=1,2,...,N; m=1,2,...,M;

[0029] Among them, x n,m (t n ) represents the received time domain echo signal of the nth array element corresponding to the mth pulse, n is the receiving array element number, m represents the signal frequency band corresponding to the mth transmitting transducer, t n is the time domain sampling point;

[0030] The frequency domain form of the output beam is

[0031] B up (k,θ i ) and B down (k,θ i ); k=1,2,...,K; i=-N,-N+1,...,N-1;

[0032] Where k is the frequency point, θ i Indicates the angle corresponding to the i-th beam of the receiving array.

[0033] In some implementations, performing dual-array phase difference vertical azimuth estimation processing on the output beam to determine the vertical azimuth corresponding to the output beam includes:

[0034] The frequency domain form of the output beams of the upper and lower linear arrays is transformed into the time domain form to obtain the complex output sequence b(i,t n ):

[0035] b up (i,t n )=IFFT[B up (k,θ i )];

[0036] b down (i,t n )=IFFT[B down (k,θ i )];

[0037] For the complex output sequence b(i,t n ) to perform conjugate complex multiplication to compensate for the vertical pointing angle β of the transmitting transducer m After that, we get the complex output sequence b z (i,t n ):

[0038] b z (i,t n )=b up (i,tn )·b* down (i,t n )·exp(-j2πDsinβ m / λ m ), i=

[0039] -N,-N+1,...,N-1;

[0040] Where * represents the complex conjugate, λ m is the wavelength corresponding to the center frequency of the pulse emitted by the mth array element;

[0041] For the complex output sequence b z (i,t n ) performs time domain smoothing operation to calculate the complex argument; the complex argument is

[0042] Among them, arg[] represents the angle operation, h(t n ) is a smoothing window function;

[0043] The complex argument φ'(i,t n ) to vertical azimuth Remove scattering points whose vertical azimuth angle exceeds the transmit beam width;

[0044] The vertical azimuth angle is

[0045]

[0046] Where D is the vertical distance between the arrays, β m is the vertical pointing angle;

[0047] Discretizing the vertical azimuth angle to determine the vertical azimuth;

[0048] The vertical orientation is

[0049] Among them, [·] is the rounding operation, The unit angle for dividing the grid.

[0050] In some implementations, performing noise suppression, coordinate transformation, and image optimization processing on the image array includes:

[0051] Performing noise suppression processing on the image array by using a threshold method;

[0052] Performing spatial linear interpolation calculation on the image array to obtain an image in a three-dimensional rectangular coordinate system;

[0053] Amplitude equalization, image filtering and / or sharpening processing are performed on the image in a three-dimensional rectangular coordinate system.

[0054] In a third aspect, the present invention further provides a wide-angle scanning imaging system, comprising:

[0055] A wide-angle scanning imaging device as described above; the transceiver processing module of the wide-angle scanning imaging device executes a wide-angle scanning imaging method as described above.

[0056] The present invention provides a wide-angle scanning imaging device method and system, which adopts a small-scale dual-linear array to improve the scanning speed, obtains a wide transmission angle through a multi-band combination method, and reduces the influence of underwater multipath interference on phase estimation; and adopts a large-bandwidth pulse waveform to improve the distance resolution, improve the phase estimation signal-to-noise ratio, reduce the influence of the lowest point reflection, and improve the 3D imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 A schematic diagram of an acoustic array of a wide-angle scanning imaging device provided by the present invention;

[0058] Figure 2 This is a schematic diagram of the structure of the wide-angle scanning imaging device provided by the present invention;

[0059] Figure 3 This is a schematic diagram of the structure of the wide-angle scanning imaging device provided by the present invention;

[0060] Figure 4 A vertical plane distribution diagram of the acoustic array transmission and receiving beams of the wide-angle scanning imaging device provided by the present invention;

[0061] Figure 5 This is a schematic diagram of the deployment of the wide-angle scanning imaging device provided by the present invention in aquaculture cages;

[0062] Figure 6 A schematic diagram of the flow chart of the wide-angle scanning imaging method provided by the present invention;

[0063] Figure 7 It is a schematic diagram of the basic processing flow of the mth transmission pulse waveform in the wide-angle scanning imaging method provided by the present invention;

[0064] Figure 8 A schematic diagram of the process of performing vertical azimuth estimation of dual linear array phase difference in the wide angle scanning imaging method provided by the present invention;

[0065] In the figure: 101, sonar probe; 102, transmitting array; 103, receiving array; 104, device body. DETAILED DESCRIPTION

[0066] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0067] The terms "including" and "having" and any variations thereof in the embodiments of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or modules is not necessarily limited to those steps or modules explicitly listed, but may include other steps or modules not explicitly listed or inherent to these processes, methods, products or apparatus.

[0068] The present application provides a wide-angle scanning imaging device, which adopts a small-scale dual-linear array to improve the scanning speed, obtains a wide transmission angle through a multi-band combination method, and reduces the influence of underwater multipath interference on phase estimation; at the same time, a large-bandwidth pulse waveform is used to improve the distance resolution, improve the phase estimation signal-to-noise ratio, reduce the influence of the lowest point (nadir area) reflection, and improve the 3D imaging quality.

[0069] In fishing and marine aquaculture, it is necessary to conduct clear and accurate three-dimensional observation of underwater fish schools. Due to the movement characteristics of fish schools, scanning imaging requires a high imaging frame rate and accurate individual positioning of fish schools. Based on the mechanical rotating scanning imaging sonar, this application improves the scanning speed and increases the 3D azimuth resolution capability to meet the needs of underwater fish school observation.

[0070] Specifically, Figure 1-4 As shown, the wide-angle scanning imaging device includes a sonar probe 101 and a device body 104. The sonar probe includes an acoustic array and a transceiver processing module; the acoustic array includes a transmitting array and a receiving array; the transmitting array includes a group of transmitting transducers, the maximum response axis of the transmitting transducers is distributed in the vertical direction according to a preset inclination angle, and the multiple transmitting beams of the transmitting transducers form a wide-angle coverage in the vertical direction; the receiving array includes an upper receiving array and a lower receiving array, and the array elements of the upper linear array and the lower linear array are arranged in an interlaced manner; the beamforming is used to distinguish in the horizontal direction, and the vertical azimuth of the echo is estimated by the phase difference of the dual array outputs; the acoustic array rotates along the central axis of the device body; the transmitting array transmits broadband orthogonal pulses according to a preset period, and the receiving array receives the echo signal, and the underwater target imaging result is obtained after being processed by the transceiver processing module according to the central frequency of the transmitting pulse of the transmitting array.

[0071] like Figure 2 As shown, the device body includes a motor control cabin, a watertight cable, a power module, a wireless transmission module and a remote image module. The motor control cabin includes a stepper motor, a motor controller, a harmonic reducer, a coupling, an electric slip ring, a power module and a data transmission module, and a watertight shell of the control cabin to control structures such as the sonar probe; the power module includes a battery pack, a photovoltaic module, a charging and protection circuit, which provides power for the wide-angle scanning imaging device.

[0072] The sonar probe includes an acoustic array, a transceiver processing module, and a watertight shell. The acoustic array adopts a large-aperture acoustic array and the probe is rotated in the external water to obtain high-resolution clear images while greatly reducing the volume and weight of the device.

[0073] like Figure 1 As shown, the acoustic array includes a transmitting array 102 and a receiving array 103; the transmitting array 102 includes a group of transmitting transducers, the maximum response axes of the transmitting transducers are distributed in the vertical direction according to a preset inclination angle, and the multiple transmitting beams of the transmitting transducers form a wide angular coverage in the vertical direction. Generally, the transmitting array is composed of a group of transmitting transducers working in different frequency bands, and 3-5 transmitting array elements are usually selected.

[0074] Each of the transmitting transducer beams includes a horizontal beam width of less than 10° and a vertical beam width of more than 10°; the vertical beam width is several times the horizontal beam width. Exemplarily, each transmitting transducer beam has a narrow horizontal beam width θ H , for example, less than 5°; at the same time, in order to obtain a larger vertical plane observation range, the transmitting beam has a wide vertical beam width θ V , for example, greater than 15°. The maximum response axis of the acoustic emission transducer, that is, the normal direction of the radiation surface, MRA, is distributed at a certain angle in the vertical direction, such as Figure 1 In and For example, the angle can be chosen to be equal to the vertical beam width of the array element. Multiple transmit beams are synthesized into wide-angle beam characteristics. The total beam width of the transmit array in the vertical direction is approximately the sum of the vertical beam widths of each array element. The transmitting transducers are centrally aligned in the horizontal direction, the MRA is consistent in the horizontal direction, there is a small spacing decoupling in the vertical direction, and they work in different frequency bands. At the same time, the radiation surface size of each transmitting array element is designed so that its transmitting beam has similar horizontal and vertical beam widths. In order to make the distance resolution of the transmitting array element pulses consistent, the transmitting waveform bandwidth is the same, and the working frequency bands do not cross each other.

[0075] The receiving array 103 adopts a dual linear array mode, including an upper receiving array and a lower receiving array, and the array elements of the upper linear array and the lower linear array are arranged in an interlaced manner; the beamforming is used to distinguish in the horizontal direction, and the vertical azimuth of the echo is estimated by the phase difference of the dual array outputs. The upper receiving array and the lower receiving array are uniform linear arrays (ULA), and the array elements of the upper linear array and the lower linear array are arranged in an interlaced manner. The array length of the upper receiving array and the lower receiving array is L, and the number of array elements is greater than L / W, where W is the length of the shortest transmitting array in the horizontal direction. The vertical distance D between the linear arrays is set, and the value range can be selected from 0.5 to 1.5λ c , where λ c is the wavelength corresponding to the median frequency of all transmitted pulses.

[0076] like Figure 3, 4 As shown, the horizontal beam width and vertical beam width of the directivity diagram of a single receiving array element are not less than the total horizontal and vertical beam widths of the transmitting array. The horizontal beam width and vertical beam width of the directivity diagram of a single receiving array element are not less than the total horizontal and vertical beam widths of the transmitting array. In this embodiment, 3 groups of transmitting transducers and a 16-element bilinear receiving array are selected to form the structure. By adjusting the size parameters of the piezoelectric ceramic sheet, the transmitting beam opening angles of the three groups of transducers are consistent, the horizontal beam width is 3°, and the vertical beam width is 15°. The frequency band centers of the transmitting transducers are 900kHz, 1.0MHz, and 1.1MHz, respectively, and the vertical directivity angles are -15°, 0°, and 15° (relative to the acoustic array plane), respectively. In order to make the distance resolution of the transmitted pulses of each array element consistent, the transmitting waveform of each array element selects a different frequency band range, which is not crossed (orthogonal) with each other and has the same bandwidth, so that the distance resolution remains consistent. In this embodiment, the signal bandwidth is designed to be 75kHz.

[0077] The scanning process is as follows Figure 2 As shown in the figure, the acoustic array plane is at an angle of 30° to the horizontal direction, which is conducive to the beam covering the underwater space. The sonar probe rotates along the central axis of the device body, and its rotation angular velocity can be selected according to the target movement, such as the activity of the fish school and the imaging distance range. In order to make the beam fully cover the observation area, the minimum angular velocity of the rotation is equal to the imaging frame rate multiplied by the horizontal opening angle of the transmitting beam.

[0078] The transmitting array elements synchronously transmit orthogonal broadband pulses, and can select the frequency band separation mode or the orthogonal coded pulse mode. The receiving array collects the echo signal, and after the transceiver processing module processes it according to the center frequency of the transmitting pulse of the transmitting array, the underwater target imaging result is obtained. In this embodiment, Figure 5 As shown, the device is installed in the aquaculture cage layout diagram. The horizontal beam width of the transmitting array is 3°, and the range is 5m~40m. Assuming the range is 15 meters, the single transmission and reception time is about 20ms, the pulse transmission frequency can reach 40Hz, and the maximum rotation angular velocity is 120° / s. The transmitting array elements synchronously transmit orthogonal broadband pulses. The frequency band separation method can be selected, or the orthogonal coded pulse can be used. In the embodiment, linear frequency modulation LFM or hyperbolic frequency modulation HFM signal is selected, and the sweep frequency range is f m ±37.5kHz, m=1,2,3; f m is the center frequency of the transmitted pulse.

[0079] Based on the above-mentioned wide-angle scanning imaging device, the present application also provides a wide-angle scanning imaging method. The underwater target imaging result obtained by this method has high resolution, reduces the impact of underwater multipath interference on phase estimation, and improves 3D imaging quality.

[0080] Specifically, Figure 6-8As shown, the method comprises the following steps:

[0081] Step S1, the transmitting array transmits broadband orthogonal pulses according to a preset period;

[0082] Step S2, the receiving array collects the echo signal, performs orthogonal modulation and downsampling according to the center frequency of the transmitting array, and obtains a baseband receiving sequence;

[0083] In order to reduce the complexity of data processing, the multi-channel received digital sequence is orthogonally demodulated according to the center frequency of each pulse, and N*M groups of baseband received sequences are obtained after downsampling:

[0084] x n,m (t n );t n =0,1,2,...,TN; n=1,2,...,N; m=1,2,...,M;

[0085] Among them, x n,m (t n ) represents the received time domain echo signal of the nth array element corresponding to the mth pulse, n is the receiving array element number, m represents the signal frequency band corresponding to the mth transmitting transducer, t n is the time domain sampling point.

[0086] like Figure 7 As shown in the figure, it is the basic processing flow of the mth transmitted pulse. After orthogonal demodulation and downsampling, it is transformed into the frequency domain form, and beamforming and matched filtering are performed on the half array respectively. The output data is divided into two paths: one path continues to complete the full array beamforming and then transforms back to the time domain form to give the horizontal beam echo intensity (amplitude) distribution, and the other path estimates the phase difference of the upper and lower array signals to give the vertical azimuth estimation of the echo.

[0087] Step S3: the upper receiving array and the lower receiving array respectively perform broadband digital beamforming processing and matched filtering processing on the baseband receiving sequence to obtain the frequency domain form of the output beam;

[0088] The frequency domain form of the output beam is

[0089] B up (k,θ i ) and B down (k,θ i ); k=1,2,...,K; i=-N,-N+1,...,N-1;

[0090] Where k is the frequency point, θ i Indicates the angle corresponding to the i-th beam of the receiving array.

[0091] Step S4: performing whole array horizontal beamforming processing on the output beam to determine the whole array beam output.

[0092] The whole array horizontal beam forming is to use the beam output of the upper and lower linear arrays with staggered receiving array elements, add them together to get the total beam output of the dual linear array, and transform them into the time domain to give the time domain output b of 2N beams. m (i,t n ):

[0093] b m (i,t n )=||IFFT[B up (k,θ i )+B down (k,θ i )]||;

[0094] where ||·|| is the modulo operation of the complex sequence, i is the beam number, t n is the time sample.

[0095] Step S5: perform dual-array phase difference vertical azimuth estimation processing on the output beam to determine the vertical azimuth corresponding to the output beam.

[0096] The output time domain sequence after pulse compression can effectively separate the scattering points in the distance dimension, improve the signal-to-noise ratio and improve the phase estimation performance. The amplitude angle can be calculated by the following formula:

[0097] φ o (i,t n )=arg[b up (i,t n )·b* down (i,t n )];

[0098] Where arg[] represents the angle operation, and * represents the complex conjugate.

[0099] Considering that there is a fixed angle between the maximum response axis of the transmitting array element and the perpendicular normal direction of the receiving array, compensation should be performed in the direction of the maximum response axis when performing phase estimation.

[0100] The formula for the compensation angle is as follows:

[0101] φ(i,t n )=arg[b up (i,t n )·b* down (i,t n )·exp(-j2πDsinβ m / λ m )];

[0102] Among them, β m is the angle between the maximum response axis of the mth transmitting array element and the horizontal plane, λm is the center frequency of the pulse transmitted by the mth array element.

[0103] From the angle φ(i,t n ) can directly give the vertical azimuth estimate

[0104]

[0105] However, the vertical azimuth calculated in the above process is easily interfered by various types of noise. In order to improve the robustness of azimuth estimation, the vertical azimuth The calculation process is as follows Figure 8 As shown, the following steps are included:

[0106] Step S51: transform the frequency domain form of the output beams of the upper linear array and the lower linear array into the time domain form to obtain a complex output sequence b(i,t n ):

[0107] b up (i,t n )=IFFT[B up (k,θ i )];

[0108] b down (i,t n )=IFFT[B down (k,θ i )];

[0109] Step S52: complex output sequence b(i,t n ) to perform conjugate complex multiplication to compensate for the vertical pointing angle β of the transmitting transducer m After that, we get the complex output sequence b z (i,t n ):

[0110] b z (i,t n )=b up (i,t n )·b* down (i,t n )·exp(-j2πDsinβ m / λ m ), i = -N, -N+1, ..., N-1;

[0111] Where * represents the complex conjugate, λ m is the wavelength corresponding to the center frequency of the pulse emitted by the mth array element;

[0112] Step S53: complex output sequence b z (i,t n) performs time domain smoothing operation to calculate the complex argument; the complex argument is

[0113] Among them, arg[] represents the angle operation, h(t n ) is a smoothing window function, such as a Hamming window, whose width is consistent with the width of the matching waveform. When the azimuth accuracy is more important than the distance accuracy, a narrow bandwidth transmit pulse waveform can be used, and a wider smoothing window function can be selected to improve the accuracy of the azimuth estimation.

[0114] Step S54: convert the complex argument φ'(i,t n ) to vertical azimuth Remove the scattering points whose vertical azimuth angle exceeds the transmit beam width; that is, the above-mentioned whole array beam output b m (i,t n ) corresponds to (i,t n ) to a negative number (invalid value).

[0115] The vertical azimuth angle is

[0116]

[0117] Where D is the vertical distance between the arrays, β m is the vertical pointing angle;

[0118] Step S55: The vertical azimuth Discretize and determine the vertical orientation; use the vertical grid number j m (i,t n ) approximates that the unit angle of the grid is You can choose according to the actual imaging effect. Between 0.5° and 2°:

[0119] The vertical orientation is

[0120] Among them, [·] is the rounding operation, The unit angle for dividing the grid.

[0121] Step S6, according to the whole array beam output and the corresponding vertical orientation, the processing results of multiple transducer pulses and the multiple transmission and reception processing results of the scanning process are comprehensively sorted to obtain an image array under the spatial polar coordinate grid;

[0122] After the above steps, the data matrices of M groups after orthogonal demodulation are processed respectively to obtain 2N*M echo amplitude sequences and the vertical azimuth j corresponding to each amplitude point 2N×M ; The whole array beam output b m (i,t n) and the corresponding vertical position j m (i,t n ), the processing results of multiple transducer pulses and the processing results of multiple transmissions and receptions during the scanning process are comprehensively sorted to obtain the image array S0(p,j,r) under the spatial polar coordinate grid, where p represents the horizontal azimuth number, j is the vertical azimuth number, and r is the corresponding distance number.

[0123] Step S7: performing noise suppression, coordinate transformation, and image optimization processing on the image array to obtain underwater target imaging results.

[0124] Specifically, they include:

[0125] Step S71, performing noise suppression processing on the image array by using a threshold method;

[0126] For the image array S0(p,j,r), for the spatial points whose amplitude is less than the threshold, the corresponding amplitude is directly set to zero. The threshold can be determined based on experience, or it can be estimated through sonar acoustic parameters and propagation attenuation process. In this application, the actual measurement method is used, that is, during the initialization of the field environment equipment, no pulses are emitted, only reception and processing are performed to give an estimate of the background noise level. Generally, 20-50 echoes are averaged along the azimuth according to the distance dimension, and α≈2-5 times the noise average value is used as the threshold. The formula is as follows:

[0127]

[0128]

[0129] Where (n) represents the number of echoes, P and J represent the number of grids in the horizontal and vertical directions within the imaging angle of view, respectively.

[0130] Step S72, performing spatial linear interpolation calculation on the image array to obtain an image in a three-dimensional rectangular coordinate system;

[0131] The image array S0(p,j,r) is subjected to spatial linear interpolation calculation to obtain the image S(x,y,z) in a three-dimensional rectangular coordinate system, which is then processed and displayed by the image visualization tool. In actual use, the imaging effect is closely related to the target object. For imaging of underwater scenes, such as the seabed and docks, no further processing is required. For imaging of spatial volume distribution targets such as schools of fish, the interference speckle noise between targets can be removed by conventional image processing methods.

[0132] Step S73: Perform amplitude equalization, image filtering and / or sharpening processing on the image in the three-dimensional rectangular coordinate system. Perform amplitude equalization, image filtering, sharpening and other general operations on S(x, y, z) in the spatial image domain to obtain underwater target imaging results that meet the needs and have good human-computer interface effects, thereby improving the display effect.

[0133] The present invention also provides a wide-angle scanning imaging system, comprising:

[0134] A wide-angle scanning imaging device as described above; the transceiver processing module of the wide-angle scanning imaging device executes a wide-angle scanning imaging method as described above.

[0135] The present invention provides a wide-angle scanning imaging device method and system, which adopts a small-scale dual-linear array to improve the scanning speed, obtains a wide transmission angle through a multi-band combination method, and reduces the influence of underwater multipath interference on phase estimation; and adopts a large-bandwidth pulse waveform to improve the distance resolution, improve the phase estimation signal-to-noise ratio, reduce the influence of the lowest point reflection, and improve the 3D imaging quality.

[0136] An embodiment of the present application also provides a non-temporary machine-readable storage medium, on which an executable program is stored. When the executable program is executed by a processor, the processor executes the wide-angle scanning imaging method provided in the above embodiment.

[0137] An embodiment of the present invention discloses a computer-readable storage medium storing a computer program for electronic data exchange, wherein the computer program enables a computer to execute the described wide-angle scanning imaging method.

[0138] An embodiment of the present invention discloses a computer program product, which includes a non-transitory computer-readable storage medium storing a computer program, and the computer program is operable to enable a computer to execute the described wide-angle scanning imaging method.

[0139] The embodiments described above are only illustrative, wherein the modules described as separate components may or may not be physically separated, and the components displayed as modules may or may not be physical modules, and may be located in one place or distributed on multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Those of ordinary skill in the art may understand and implement it without creative work.

[0140] Through the specific description of the above embodiments, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the above technical solution can be essentially or partly contributed to the prior art in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, and the storage medium includes a read-only memory (ROM), a random access memory (RAM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), a one-time programmable read-only memory (OTPROM), an electronically erasable rewritable read-only memory (EEPROM), a compact disc (CD-ROM) or other optical disc storage, a magnetic disk storage, a magnetic tape storage, or any other computer-readable medium that can be used to carry or store data.

[0141] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A wide-angle scanning imaging device, characterized in that: It includes a sonar probe and a device body; The sonar probe includes an acoustic array and a transceiver processing module; the acoustic array includes a transmitting array and a receiving array; the transmitting array includes a group of transmitting transducers, the maximum response axes of the transmitting transducers are distributed in the vertical direction according to a preset inclination angle, and the multiple transmitting beams of the transmitting transducers form a wide angular coverage in the vertical direction; The receiving array comprises an upper receiving array and a lower receiving array, and the array elements of the upper receiving array and the lower receiving array are arranged alternately; the beamforming is used for resolution in the horizontal direction, and the vertical azimuth of the echo is estimated by the phase difference output by the dual arrays; The acoustic array rotates along the central axis of the device body; the transmitting array transmits broadband orthogonal pulses according to a preset period, and the receiving array receives the echo signal. After being processed by the transceiver processing module according to the central frequency of the transmitting pulse of the transmitting array, the underwater target imaging result is obtained.

2. A wide-angle scanning imaging device according to claim 1, characterized in that: The beam of each transmitting transducer includes a horizontal beam width of less than 10° and a vertical beam width of more than 10°; the vertical beam width is several times the horizontal beam width; The transmitting transducers are centrally aligned in the horizontal direction and have a preset spacing in the vertical direction for decoupling; each transmitting transducer has a different operating frequency band; The transmitting transducer transmits broadband orthogonal pulses according to a preset period, and adopts a frequency-division or code-division orthogonal waveform design.

3. The wide-angle scanning imaging device according to claim 2, characterized in that: The upper receiving array and the lower receiving array are uniform linear arrays, with an array length of L and an array element number greater than L / W, where W is the length of the shortest transmitting array in the horizontal direction; the vertical distance between the linear arrays of the receiving arrays ranges from 0.5 to 1.5λ c ,λ c is the wavelength corresponding to the median frequency of all transmitted pulses.

4. The wide-angle scanning imaging device according to claim 3, characterized in that: The plane of the acoustic array forms an angle of 25° to 35° with the horizontal direction.

5. The wide-angle scanning imaging device according to claim 3, characterized in that: The angular velocity of the rotational motion is equal to the product of the imaging frame rate and the horizontal opening angle of the transmitting beam.

6. A wide-angle scanning imaging method, characterized in that: Applied to the wide-angle scanning imaging device as claimed in any one of claims 1 to 5, the method comprises the following steps: The transmitting array transmits broadband orthogonal pulses according to a preset period; The receiving array collects the echo signal, performs orthogonal modulation and down-sampling according to the center frequency of the transmitting array, and obtains a baseband receiving sequence; The upper receiving array and the lower receiving array respectively perform broadband digital beamforming processing and matched filtering processing on the baseband receiving sequence to obtain the frequency domain form of the output beam; Performing whole array horizontal beamforming processing on the output beam to determine the whole array beam output; Performing dual-array phase difference vertical azimuth estimation processing on the output beam to determine the vertical azimuth corresponding to the output beam; According to the whole array beam output and the corresponding vertical orientation, the processing results of multiple transducer pulses and the multiple transmission and reception processing results of the scanning process are comprehensively sorted to obtain an image array under a spatial polar coordinate grid; The image array is subjected to noise suppression, coordinate transformation, and image optimization processing to obtain underwater target imaging results.

7. A wide-angle scanning imaging method according to claim 6, characterized in that: The baseband receiving sequence is x n,m (t n ),t n =0,1,2,...,TN;n=1,2,...,N;m=1,2,...,M; Among them, x n,m (t n ) represents the received time domain echo signal of the nth array element corresponding to the mth pulse, n is the receiving array element number, m represents the signal frequency band corresponding to the mth transmitting transducer, t n is the time domain sampling point; The frequency domain form of the output beam is B up (k,θ i ) and B down (k,θ i );k=1,2,...,K;i=-N,-N+1,...,N-1; Where k is the frequency point, θ i Indicates the angle corresponding to the i-th beam of the receiving array.

8. The wide-angle scanning imaging method according to claim 7, characterized in that: Perform dual-array phase difference vertical azimuth estimation processing on the output beam to determine the vertical azimuth corresponding to the output beam, including: The frequency domain form of the output beams of the upper receiving array and the lower receiving array is transformed into the time domain form to obtain the complex output sequence b(i,t n ): b up (i,t n )=IFFT[B up (k,θ i )]; b down (i,t n )=IFFT[B down (k,θ i )]; For the complex output sequence b(i,t n ) to perform conjugate complex multiplication to compensate for the vertical pointing angle β of the transmitting transducer m , and get the complex output sequence b z (i,t n ): b z (i,t n )=b up (i,t n )·b* down (i,t n )·exp(-j2πDsinβ m / λ m ),i= -N,-N+1,...,N-1; Where * represents the complex conjugate, λ m is the wavelength corresponding to the center frequency of the pulse emitted by the mth array element; For the complex output sequence b z (i,t n ) performs time domain smoothing operation to calculate the complex argument; the complex argument is Among them, arg[] represents the angle operation, h(t n ) is a smoothing window function; The complex argument φ'(i,t n ) to vertical azimuth Remove scattering points whose vertical azimuth angle exceeds the transmit beam width; The vertical azimuth angle is Where D is the vertical distance between the arrays, β m is the vertical pointing angle; Discretizing the vertical azimuth angle to determine the vertical azimuth; The vertical orientation is Among them, [·] is the rounding operation, The unit angle for dividing the grid.

9. The wide-angle scanning imaging method according to claim 6, characterized in that: The image array is subjected to noise suppression, coordinate transformation, and image optimization processing, including: Performing noise suppression processing on the image array by using a threshold method; Performing spatial linear interpolation calculation on the image array to obtain an image in a three-dimensional rectangular coordinate system; Amplitude equalization, image filtering and / or sharpening processing are performed on the image in a three-dimensional rectangular coordinate system.

10. A wide-angle scanning imaging system, characterized in that: include: A wide-angle scanning imaging device as described in claims 1 to 5; the transceiver processing module of the wide-angle scanning imaging device executes a wide-angle scanning imaging method as described in claims 6 to 9.

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