Wide-angle scanning imaging device, method and system

Abstract

Disclosed in the present invention are a wide-angle scanning imaging device, method and system. The device comprises a sonar probe and a device body. The sonar probe comprises an acoustic array and a transceiving processing module. The acoustic array comprises a transmitting array and a receiving array. The transmitting array comprises a group of transmitting transducers. Maximum response axes of the transmitting transducers are distributed in the vertical direction according to preset tilt angles, and a plurality of transmitted beams of the transmitting transducers form wide-angle coverage in the vertical direction. The receiving array performs resolution in the horizontal direction by means of beamforming, and vertical orientations of echoes are estimated by means of double-array output phase differences. The acoustic array performs rotational motion along the central axis of the device body. The transmitting array transmits broadband orthogonal pulses according to a preset period, the receiving array receives echo signals, and the transceiving processing module processes the echo signals according to the central frequency of the transmitted pulses of the transmitting array to obtain an underwater target imaging result. The present invention reduces the impact of underwater multipath interference and the like on phase estimation and improves the 3D imaging quality.

Description

A wide-angle scanning imaging device, method, system TECHNICAL FIELD

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

[0002] In the field of underwater acoustic imaging, scanning imaging technology combines echo sequences through multiple emission-reception operations to obtain a scanning image. Due to scanning imaging, spatial beam sidelobes are reduced, and image range resolution is improved through pulse compression, so that high-quality image results can be obtained in applications. Currently, related side-scan sonars and rotating scanning sonars have been widely used.

[0003] The patent “360 Degree Imaging Sonar and Method” (US9322915B2) increases the scanning imaging frame rate by one time through mechanical rotation of two groups of acoustic transducers in the sonar sound-transparent cabin. In order to facilitate underwater fish observation, the sonar transducer radiation surface is installed at an angle, so that the sonar has a desired downwardly inclined beam opening angle. In order to obtain better resolution performance, the Seaking Hammerhead scanning sonar of the Tritech company uses a large-size dual-frequency sonar probe, and scanning imaging is completed 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 double-path 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 requires a long time, so this type of sonar is usually more suitable for imaging static underwater scenes.

[0004] In order to improve the scanning speed, a beam forming method is used to generate multiple receiving beams within a wide horizontal transmission angle, so that the seafloor can still be covered at high speeds. For example, the 5900 type side-scan sonar of the Klein Ocean Systems company, under the condition of a wide horizontal transmission angle, multiple echo processes can be integrated to obtain a synthetic aperture processing effect. The patent CN110196428A uses two orthogonal transmission transducers to obtain a virtual array aperture of about 2 times the array length.

[0005] In some applications, three-dimensional imaging of underwater scenes is necessary, and it is desirable to obtain underwater 3D scanning imaging results. The existing technology gives image information in the vertical direction by increasing the acoustic array perpendicular to the mechanical scanning direction, such as the BV5000 sonar of the Blueview company. In some applications (such as US7215198 B2), vertical direction scanning is performed through beam steering transmission, and the horizontal plane is realized by receiving array beam forming.

[0006] In order to accelerate the speed of emission scanning, the prior art (CN201410176890.1) realizes pulse orthogonality in different vertical directions through multi-pulse technology or MIMO system. The above-mentioned 3D imaging methods all need multi-element arrays and multi-channel beam control transmitter devices in the vertical direction. Another type of technical approach measures the echo arrival direction in the vertical plane through the phase difference of the receiving array. In this way, the vertical direction only needs two array elements to be distinguished, which is called interferometric side-scan sonar. However, due to the fact that the phase difference direction finding is easily affected by multiple decorrelation factors and noise interference, and there is a problem of phase ambiguity, the differential interference method (Vernier method) or multi-phase differential interference method (MPDI) is generally used to increase the robustness of phase estimation and improve the imaging quality, and is practically applied in various depth-scan sonar systems.

[0007] In the context of fishing and mariculture, it is necessary to clearly and accurately observe the underwater fish group in three dimensions. The cost constraint makes it difficult for multi-element, high-frame-rate imaging systems such as forward-looking sonar and 3D imaging sonar to be practically applied. SUMMARY

[0008] To solve the above problems, a wide-angle scanning imaging device, method and system are provided to improve 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 application provides a wide-angle scanning imaging device, which comprises a sonar probe and a device body.

[0010] 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 according to a preset inclination angle in the vertical direction, and a plurality of transmitting beams of the transmitting transducers form a wide-angle coverage in the vertical direction.

[0011] The receiving array comprises an upper receiving array and a lower receiving array, and the elements of the upper receiving array and the lower receiving array are staggered. The horizontal direction is distinguished by beam forming, and the vertical direction of the echo is estimated by the phase difference of the double-array output.

[0012] The acoustic array rotates along the central axis of the device body. The transmitting array transmits wideband orthogonal pulses at a preset period, the receiving array receives echo signals, and after processing by the transceiver processing module according to the center 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 is less than 10° in horizontal beam width and more than 10° in vertical beam width; and the vertical beam width is several times the width of the horizontal beam width.

[0014] The transmitting transducers are horizontally center-aligned and vertically decoupled with a preset interval; and each of the transmitting transducers has a different operating frequency band.

[0015] The transmitting transducers emit wideband orthogonal pulses at a preset period, and frequency division or code division orthogonal waveform design is adopted.

[0016] In some embodiments, the upper receiving array and the lower receiving array are uniform linear arrays, the array length 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 between the linear arrays of the receiving array ranges from 0.5λ to 1.5λ. c c λ is the wavelength corresponding to the intermediate frequency of all transmitting 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 rotating motion is equal to the product of the imaging frame rate and the horizontal opening angle of the transmitting beam.

[0019] In a second aspect, the present application 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 emits wideband orthogonal pulses at a preset period;

[0021] The receiving array collects echo signals, and performs orthogonal demodulation and downsampling according to the center frequency of the transmitting array to obtain a baseband receiving sequence;

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

[0023] The output beam is subjected to whole-array horizontal beamforming processing to determine the whole-array beam output;

[0024] The output beam is subjected to double-array phase difference vertical azimuth estimation processing to determine the vertical azimuth corresponding to the output beam;

[0025] According to the whole-array beam output and the corresponding vertical azimuth, the processing results of multiple transducer pulses and the multiple times of receiving and transmitting processing results in the scanning process are comprehensively sorted to obtain an image array in a spatial polar coordinate grid;

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

[0027] In some embodiments, the baseband receiving sequence is x n,m (t​n ), t n = 0, 1, 2,..., TN; n = 1, 2,..., N; m = 1, 2,..., M;

[0028] wherein 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 sequence number of the receiving array element, m represents the signal frequency band corresponding to the mth transmitting transducer, t n is the time-domain sampling point;

[0029] 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;

[0030] wherein k is the frequency point, and θ i represents the angle corresponding to the ith beam of the receiving array.

[0031] In some embodiments, the output beam is subjected to a double-array phase difference vertical azimuth estimation process to determine the vertical azimuth corresponding to the output beam, comprising:

[0032] The frequency-domain form of the output beam of the upper receiving array and the lower receiving array is transformed to the time-domain form to obtain a 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 )];

[0033] The complex output sequence b(i, t n ) is subjected to a conjugate complex multiplication operation to compensate for the vertical pointing angle β m of the transmitting transducer, and a complex output sequence b z (i, t n ) is obtained: 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;

[0034] wherein * represents complex conjugate, λ m is the center frequency of the m-th array element pulse corresponding wavelength;

[0035] performing time domain smoothing operation on the complex output sequence b z (i,t n ), calculating complex amplitude angle; the complex amplitude angle is

[0036] wherein arg[] represents amplitude angle operation, h(t n ) is a smoothing window function;

[0037] transforming the complex amplitude angle φ'(i,t n ) to vertical azimuth angle removing scattering points whose vertical azimuth angle exceeds the width of the transmitting beam;

[0038] the vertical azimuth angle is

[0039] wherein D is the vertical distance between linear arrays, β m is the vertical pointing angle;

[0040] discretizing the vertical azimuth angle to determine the vertical direction;

[0041] the vertical direction is

[0042] wherein [·] is the rounding operation, is the unit angle of the divided grid.

[0043] In some embodiments, the image array is subjected to noise suppression, coordinate conversion, image optimization processing, including:

[0044] the image array is subjected to noise suppression processing by threshold method;

[0045] the image array is subjected to spatial linear interpolation calculation to obtain an image in three-dimensional rectangular coordinate system;

[0046] the image in three-dimensional rectangular coordinate system is subjected to amplitude equalization, image filtering and / or sharpening processing.

[0047] In a third aspect, the present application further provides a wide-angle scanning imaging system, comprising:

[0048] a wide-angle scanning imaging device as described above; the transceiving processing module of the wide-angle scanning imaging device performs a wide-angle scanning imaging method as described above.

[0049] The application provides a wide-angle scanning imaging device method and system, which adopts a small-scale bilinear array to improve scanning speed, obtains a wide emission angle through a multi-band combination mode, and reduces the influence of underwater multipath interference on phase estimation; and adopts a large-bandwidth pulse waveform to improve distance resolution, improve phase estimation signal-to-noise ratio, reduce the influence of the lowest point reflection, and improve 3D imaging quality. BRIEF DESCRIPTION OF DRAWINGS

[0050] Fig. 1 is a schematic diagram of an acoustic array of the wide-angle scanning imaging device provided by the application;

[0051] Fig. 2 is a schematic diagram of the structure of the wide-angle scanning imaging device provided by the application;

[0052] Fig. 3 is a schematic diagram of the structure of the wide-angle scanning imaging device provided by the application;

[0053] Fig. 4 is a vertical plane distribution diagram of the acoustic array transmission and receiving beams of the wide-angle scanning imaging device provided by the application;

[0054] Fig. 5 is a schematic diagram of the wide-angle scanning imaging device provided by the application in a net cage layout;

[0055] Fig. 6 is a schematic diagram of the flow of the wide-angle scanning imaging method provided by the application;

[0056] Fig. 7 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 application;

[0057] Fig. 8 is a schematic diagram of the flow of the bilinear array phase difference vertical azimuth estimation in the wide-angle scanning imaging method provided by the application;

[0058] In the drawings: 101, sonar probe; 102, transmission array; 103, receiving array; 104, device body. DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0060] The application will be further described in detail below with reference to the drawings.

[0061] The terms "comprising" and "having" and any variations thereof herein are intended to cover a process, method, system, product, or apparatus both exclusively and non-exclusively, for example, a process, method, system, product, or apparatus that includes a list of steps or modules as expressly identified in the specification is not necessarily limited to only those steps or modules expressly identified as techniques that can be performed at the same time as other steps or modules are performed are also within the scope of the present application.

[0062] The present application provides a wide-angle scanning imaging device, which uses a small-scale bilinear array to improve scanning speed, obtains a wide emission angle through a multi-band combination method, and reduces the influence of underwater multipath interference on phase estimation; meanwhile, a large-bandwidth pulse waveform is used to improve range resolution, improve phase estimation signal-to-noise ratio, reduce the influence of nadir reflection, and improve 3D imaging quality.

[0063] In fishing and mariculture, it is necessary to clearly and accurately observe the underwater fish group in three dimensions. Due to the motion characteristics of the fish group, scanning imaging needs to have a high imaging frame rate and accurate individual positioning of the fish group. The present application improves the scanning speed and increases the 3D azimuth resolution capability on the basis of a mechanical rotary scanning imaging sonar, thereby meeting the needs of underwater fish group observation.

[0064] Specifically, as shown in FIGS. 1-4, the wide-angle scanning imaging device includes a sonar probe 101 and a device body 104. The sonar probe includes an acoustic array, a transceiving 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 according to a preset inclination angle in the vertical direction, and a plurality of 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, the elements of the upper receiving array and the lower receiving array are staggered; the horizontal direction is distinguished by beam forming, and the vertical direction of the echo is estimated by the phase difference of the double-array output; the acoustic array rotates along the central axis of the device body; the transmitting array transmits a wideband orthogonal pulse according to a preset period, the receiving array receives a return signal, and after being processed by the transceiving processing module according to the center frequency of the transmitting pulse of the transmitting array, an underwater target imaging result is obtained.

[0065] As shown in FIG. 2, the device body includes a motor control cabin, a water-tight cable, a power module, a wireless transmission module, and a remote image module, the motor control cabin includes a stepping motor, a motor controller, a harmonic reducer, a shaft coupling, an electric slip ring, a power module, and a data transmission module, and a control cabin water-tight shell, to control the sonar probe and other structures; the power module includes a battery pack, a photovoltaic module, a charging and protection circuit, to supply power for the wide-angle scanning imaging device.

[0066] The sonar probe comprises an acoustic array, a transceiving processing module and a water-tight shell, the acoustic array adopts a large-aperture acoustic array, the probe rotates in external water to obtain a high-resolution clear image and greatly reduce the volume and weight of the device.

[0067] As shown in FIG. 1, the acoustic array comprises a transmitting array 102 and a receiving array 103; the transmitting array 102 comprises a group of transmitting transducers, the maximum response axes of the transmitting transducers are distributed at preset inclination angles in the vertical direction, and a plurality of transmitting beams of the transmitting transducers form wide-angle coverage in the vertical direction. Generally, the transmitting array is composed of a group of transmitting transducers working in different frequency bands, and usually 3-5 transmitting array elements are selected.

[0068] The beam of each transmitting transducer comprises a horizontal beam width less than 10° and a vertical beam width more than 10°; the vertical beam width is several times the width of the horizontal beam width. Exemplarily, each transmitting transducer beam has a narrow horizontal beam width θ H , for example, less than 5°; and in order to obtain a larger vertical plane observation range, the transmitting beam has a wide vertical beam width θ V , for example, more than 15°. The maximum response axis of the acoustic transmitting transducer, that is, the normal direction of the radiation surface, MRA, is distributed at a certain angle in the vertical direction, as shown in FIG. 1. and For example, the included angle can be selected to be equal to the vertical beam width of the array element, and the wide-angle beam characteristics of the plurality of transmitting beams are combined, and the total beam width of the transmitting array in the vertical direction is about the sum of the vertical beam widths of the array elements. The transmitting transducers are horizontally centered and aligned, the MRA is consistent in the horizontal direction, and there is a small spacing in the vertical direction to decouple, and they work in different frequency bands. At the same time, the size of the radiation surface of each transmitting array element is designed so that the transmitting beams have similar horizontal and vertical beam widths. In order to make the distance resolution of the transmitting array element pulse consistent, the transmitting waveform bandwidth is the same, and the working frequency bands do not overlap.

[0069] The receiving array 103 adopts a bilinear array, comprising an upper receiving array and a lower receiving array, and the array elements of the upper receiving array and the lower receiving array are staggered; the horizontal direction is distinguished by beam forming, and the vertical direction of the echo is estimated by the phase difference of the double-array output. The upper receiving array and the lower receiving array are uniform linear arrays (ULA), the array elements of the upper receiving array and the lower receiving array are staggered, 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, wherein W is the length of the shortest transmitting array in the horizontal direction. The vertical distance D between the line arrays is selected in the range of 0.5-1.5λ c , wherein λ c is the wavelength corresponding to the intermediate frequency of all transmitting pulses.

[0070] As shown in FIG. 3 and FIG. 4, the horizontal beam width and the vertical beam width of the single receiving array element directivity diagram are not less than the total horizontal and vertical beam width of the transmitting array. In the embodiment, three groups of transmitting transducers and a 16-element bilinear receiving array are selected to form the wide-angle scanning imaging device, and the size parameters of the piezoelectric ceramic sheet are adjusted so that 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 900 kHz, 1.0 MHz and 1.1 MHz respectively, and the vertical pointing angles are -15°, 0° and 15° (relative to the plane of the acoustic array) respectively. In order to make the distance resolution of the pulses transmitted by each array element consistent, the transmitting waveforms of each array element are selected to be in different frequency band ranges, and the frequency band ranges do not overlap (orthogonal) and have the same bandwidth, so that the distance resolution remains consistent. In the embodiment, the signal bandwidth is designed to be 75 kHz.

[0071] The process of scanning imaging is shown in FIG. 2. The plane of the acoustic array forms an angle of 30° with the horizontal direction, which is beneficial to the beam coverage of the underwater space. The sonar probe rotates along the central axis of the device body, and the rotational angular velocity can be selected according to the target motion, such as the activity of the fish school and the imaging distance range. In order to make the beam completely cover the observation area, the minimum angular velocity of the rotational motion is equal to the imaging frame rate multiplied by the horizontal opening angle of the transmitting beam.

[0072] The transmitting array synchronously transmits orthogonal broadband pulses, which can be selected in a frequency band separation manner or by using orthogonal coded pulses. The receiving array collects echo signals, which are processed by the transceiving processing module according to the center frequency of the transmitting pulse of the transmitting array to obtain the underwater target imaging result. In the embodiment, as shown in FIG. 5, the device is installed in the layout diagram of the net cage for aquaculture. The horizontal beam width of the transmitting array is 3°, and the range is 5m-40m which can be selected. Assuming that the range is selected to be 15m, the single transceiving time is about 20ms, the pulse transmitting frequency can reach 40Hz, and the maximum rotational angular velocity is 120° / s. The transmitting array synchronously transmits orthogonal broadband pulses, which can be selected in a frequency band separation manner or by using orthogonal coded pulses. In the embodiment, linear frequency modulation (LFM) or hyperbolic frequency modulation (HFM) signals are selected, the sweep frequency range is f m ±37.5kHz, m = 1, 2, 3; f m is the center frequency of the transmitting pulse.

[0073] Based on the wide-angle scanning imaging device described above, the application further provides a wide-angle scanning imaging method. The underwater target imaging result obtained by the method has high resolution, reduces the influence of underwater multipath interference on phase estimation, and improves the 3D imaging quality.

[0074] Specifically, as shown in FIG. 6-8, the method comprises the following steps:

[0075] Step S1, the transmitting array transmits a wideband orthogonal pulse according to a preset period;

[0076] Step S2, the receiving array collects echo signals, and performs orthogonal demodulation and downsampling according to the center frequency of the transmitting array to obtain a baseband receiving sequence;

[0077] In order to reduce the complexity of data processing, the multi-channel receiving digital sequence is respectively demodulated according to the center frequency of each pulse, and after downsampling, N*M groups of baseband receiving sequences are obtained: x n,m (t n ); t n =0,1,2,...,TN; n=1,2,...,N; m=1,2,...,M;

[0078] Wherein, x n,m (t n ) represents the receiving time domain echo signal of the nth array element corresponding to the mth pulse, n is the array element number, m represents the signal frequency band corresponding to the mth transmitting transducer, and t n is a time domain sampling point.

[0079] As shown in FIG. 7, it is a basic processing flow of the mth transmitting pulse, which is transformed into a frequency domain form after orthogonal demodulation and downsampling, and the half array is respectively subjected to beam forming and matched filtering, and the output data is divided into two paths: one path is transformed back to a time domain form after completing full array beam forming, and horizontal beam echo intensity (amplitude) distribution is given, and the other path is subjected to up-down array signal phase difference estimation, and vertical direction estimation of the echo is given.

[0080] Step S3, the upper receiving array and the lower receiving array respectively perform wideband digital beam forming processing and matched filtering processing on the baseband receiving sequence to obtain a frequency domain form of an output beam;

[0081] 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;

[0082] Wherein, k is a frequency point, and θ i represents an angle corresponding to the ith beam of the receiving array.

[0083] Step S4, performing full array horizontal beam forming processing on the output beam to determine full array beam output.

[0084] The full array horizontal beam forming is to add the beam outputs of the upper and lower linear arrays of the receiving array elements arranged in an interlaced manner to obtain the total beam output of the double linear array, and the total beam output is transformed into a time domain to give a time domain output b m(i,t n ): b m (i,t n )=||IFFT[B up (k,θ i )+B down (k,θ i )]||;

[0085] Where ||·|| represents the modulo operation of the complex sequence, i is the beam number, and t is the beam number. n For time sampling.

[0086] Step S5: Perform dual-array phase difference vertical azimuth estimation on the output beam to determine the vertical azimuth of the output beam.

[0087] The pulse-compressed output time-domain sequence can effectively separate the scattering points in the range dimension, improving the signal-to-noise ratio and phase estimation performance. The amplitude can be calculated using the following formula: φ o (i,t n ) = arg[b up (i,t n )·b* down (i,t n )];

[0088] Where arg[] represents argument operation, and * represents complex conjugate.

[0089] Considering that the maximum response axis of the transmitting array element has a fixed angle with the perpendicular normal direction of the receiving array, compensation should be made according to the direction of the maximum response axis when performing phase estimation.

[0090] The formula for the compensated argument angle is as follows: φ(i,t) n ) = arg[b up (i,t n )·b* down (i,t n )·exp(-j2πDsinβ m / λ m )];

[0091] Where, β m λ is the angle between the maximum response axis of the m-th transmitting element and the horizontal plane. m It is the center frequency of the pulse emitted by the m-th element.

[0092] From the argument φ(i,t) n The vertical azimuth angle can be directly estimated.

[0093] However, the vertical azimuth calculated by the above process is easily affected by various types of noise. In order to improve the robustness of the azimuth estimation, the vertical azimuth... The calculation flow of the method is shown in FIG. 8, including the following steps:

[0094] Step S51, transform the frequency domain form of the output beams of the upper receiving array and the lower receiving array to the time domain form to obtain a 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 )];

[0095] Step S52, perform a conjugate complex multiplication operation on the complex output sequence b(i, t n ) to compensate for the vertical pointing angle β m of the transmitting transducer, to obtain a 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

[0096] wherein * represents a complex conjugate, λ m is the wavelength corresponding to the center frequency of the m-th element transmitting pulse;

[0097] Step S53, perform a time domain smoothing operation on the complex output sequence b z (i, t n ) to calculate a complex amplitude angle; the complex amplitude angle is

[0098] wherein arg[] represents an amplitude angle operation, and h(t n ) is a smoothing window function; for example, a Hamming window, the width of which is consistent with the width of the matched waveform. When the azimuth accuracy is more important than the range accuracy, a transmitting pulse waveform with a narrower bandwidth can be used, and a wider smoothing window function can be selected to improve the azimuth estimation accuracy.

[0099] Step S54, transform the complex amplitude angle φ'(i, t n ) to a vertical azimuth angle to remove scattering points whose vertical azimuth angle exceeds the width of the transmitting beam; that is, the above whole-array beam output bm (i,t n ) of the corresponding (i,t n ) is changed to a negative number (invalid value).

[0100] The vertical azimuth is

[0101] where D is the vertical distance between the linear arrays, β m is the vertical pointing angle;

[0102] Step S55, discretize the vertical azimuth to determine the vertical azimuth; the vertical direction grid number j m (i,t n ) is approximately represented, and the unit angle of the grid is which can be selected according to the actual imaging effect, and is generally between 0.5° and 2°:

[0103] The vertical azimuth is

[0104] where [·] is the rounding operation, and the unit angle of the grid is

[0105] Step S6, according to the whole array beam output and the corresponding vertical azimuth, the processing results of the multiple transducer pulses and the multiple times of receiving and processing results in the scanning process are comprehensively sorted to obtain an image array under the spatial polar coordinate grid.

[0106] After the above steps, the M groups of data matrices after orthogonal demodulation are processed respectively to obtain 2N*M echo amplitude sequences and the corresponding vertical azimuth j 2N×M of each amplitude point; according to the whole array beam output b m (i,t n ) and the corresponding vertical azimuth j m (i,t n ), the processing results of the multiple transducer pulses and the multiple times of receiving and processing results in the scanning process are comprehensively sorted to obtain an image array S0(p,j,r) under the spatial polar coordinate grid, where p represents the horizontal position sequence number, j is the vertical azimuth sequence number, and r is the corresponding distance sequence number.

[0107] Step S7, noise suppression, coordinate conversion and image optimization processing are performed on the image array to obtain the underwater target imaging result.

[0108] Specifically, it includes:

[0109] Step S71, the image array is processed by a threshold method for noise suppression;

[0110] For the image array S0(p,j,r), for the spatial point with amplitude less than the threshold, the corresponding amplitude is directly set to zero. The threshold can be determined according to experience, or can be estimated by the sonar acoustic parameters and propagation attenuation process. In this application, the measured method is adopted, that is, during the initialization process of the field environment device, no pulse is emitted, only receiving processing is performed, an estimation of the background noise level is given, generally 20-50 times of echoes are averaged along the azimuth direction according to the distance dimension, and the threshold is 2-5 times of the noise average value, and the formula is expressed as follows:

[0111] Wherein, (n) represents the echo number, P and J are the grid numbers of the horizontal azimuth and vertical azimuth in the imaging angle respectively.

[0112] Step S72, performing spatial linear interpolation calculation on the image array to obtain an image in a three-dimensional rectangular coordinate system;

[0113] The spatial linear interpolation calculation is performed on the image array S0(p,j,r) to obtain an image S(x,y,z) in a three-dimensional rectangular coordinate system, and then the image is processed and displayed by an image visualization tool. In actual use, the imaging effect is closely related to the target object. For underwater scene imaging, such as seabed and wharf, no further processing is required. For imaging of spatial volume distribution targets such as fish schools, the interference speckle noise between targets can be removed by conventional image processing methods.

[0114] Step S73, performing amplitude equalization, image filtering and / or sharpening processing on the image in the three-dimensional rectangular coordinate system. The amplitude equalization, image filtering, sharpening and other general operations are performed on S(x,y,z) in the spatial image domain to obtain underwater target imaging results that meet the needs and have good human-machine interface effects, and the display effect is improved.

[0115] The application also provides a wide-angle scanning imaging system, comprising:

[0116] The wide-angle scanning imaging device as described above; and the transceiving processing module of the wide-angle scanning imaging device performs the wide-angle scanning imaging method as described above.

[0117] The application provides a wide-angle scanning imaging device method and system, which uses a small-scale bilinear array to improve the scanning speed, uses a multi-band combination method to obtain a wide transmission angle, reduces the influence of underwater multipath interference on phase estimation, uses a large-bandwidth pulse waveform to improve the distance resolution, improves the signal-to-noise ratio of phase estimation, reduces the influence of the lowest point reflection, and improves the 3D imaging quality.

[0118] The embodiment of the present application further provides a non-transitory machine readable storage medium, which stores an executable program, and when the executable program is run by a processor, the processor executes the wide-angle scanning imaging method provided by the above embodiment.

[0119] The embodiment of the present application discloses a computer readable storage medium, which stores a computer program for electronic data exchange, wherein the computer program causes a computer to execute the wide-angle scanning imaging method described.

[0120] The embodiment of the present application discloses a computer program product, which comprises a non-transitory computer readable storage medium storing a computer program, and the computer program is operable to cause a computer to execute the wide-angle scanning imaging method described.

[0121] The above described embodiments are only illustrative, wherein the modules described as separate components can or can not be physically separated, the components displayed as modules can or can not be physical modules, and can be located in one place or distributed on multiple network modules. Part or all of the modules can be selected to achieve the purpose of the embodiment scheme according to actual needs. Those skilled in the art can understand and implement without creative labor.

[0122] Those skilled in the art can clearly understand the implementation of the various embodiments by means of software and necessary general hardware platforms through the specific description of the above embodiments, and of course, the embodiments can also be implemented by hardware. Based on such understanding, the above technical solutions can be embodied in the form of a software product, and the computer software product can be stored in a computer readable storage medium, which 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 Electrically-Erasable Programmable Read-Only Memory (EEPROM), a Compact Disc Read-Only Memory (CD-ROM) or other optical disk storage, a magnetic disk storage, a magnetic tape storage, or any other medium that can be used to carry or store data in a computer readable manner.

[0123] The above only describes some embodiments of the present application. Those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A wide-angle, scanning imaging device, characterized by, 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 axes of the transmitting transducers are distributed according to preset inclination angles in the vertical direction, and a plurality of transmitting beams of the transmitting transducers form wide-angle coverage in the vertical direction. The receiving array comprises an upper receiving array and a lower receiving array, the elements of the upper receiving array and the lower receiving array are staggered, the resolution is achieved in the horizontal direction through beam forming, and the vertical direction of the echo is estimated by the phase difference of the double-array output.

2. A wide-angle imaging device according to claim 1, wherein The acoustic array rotates along the central axis of the device body, the transmitting array transmits wideband orthogonal pulses at a preset period, the receiving array receives echo signals, and the underwater target imaging result is obtained after the transceiver processing module processes the echo signals according to the center frequency of the transmitting pulse of the transmitting array. The beam of each transmitting transducer comprises a horizontal beam width less than 10° and a vertical beam width more than 10°, and the vertical beam width is several times the width of the horizontal beam width. The transmitting transducers are centrally aligned in the horizontal direction and have a preset spacing for decoupling in the vertical direction.

3. A wide-angle imaging device according to claim 2, wherein 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, wherein W is the length of the shortest transmitting array in the horizontal direction; the vertical distance between the linear arrays of the receiving array is in the range of 0.5-1.5λ c , λ c is the wavelength corresponding to the intermediate frequency of all transmitting pulses.

4. A wide-angle imaging device according to claim 3, wherein The transmitting transducers transmit wideband orthogonal pulses at a preset period, and frequency division or code division orthogonal waveform design is adopted.

5. A wide-angle imaging device according to claim 3, wherein The plane of the acoustic array forms an angle of 25°-35° with the horizontal direction.

6. A wide-angle scanning imaging method, characterized by, The angular velocity of the rotation is equal to the product of the imaging frame rate and the horizontal opening angle of the transmitting beam. The method is applied to the wide-angle scanning imaging device of any one of claims 1-5, and comprises the following steps: The transmitting array transmits wideband orthogonal pulses at a preset period; The receiving array collects echo signals, performs orthogonal modulation and downsampling 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 wideband digital beam forming processing and matched filtering processing on the baseband receiving sequence to obtain the frequency domain form of the output beam; The output beam is subjected to whole-array horizontal beam forming processing to determine the whole-array beam output; The output beam is subjected to double-array phase difference vertical direction estimation processing to determine the vertical direction corresponding to the output beam; The processing results of a plurality of transducer pulses and the multiple transceiver processing results in the scanning process are comprehensively sorted according to the whole-array beam output and the corresponding vertical direction to obtain an image array in a spatial polar coordinate grid; 7. A wide-swath angular scanning imaging method according to claim 6, wherein, The baseband receiving sequence is x n,m (t n ), t n = 0, 1, 2,..., TN; n = 1, 2,..., N; m = 1, 2,..., M; wherein 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 array element sequence number of the receiving array, m represents the signal frequency band corresponding to the mth transmitting transducer, t n is the time-domain sampling point; The image array is subjected to noise suppression, coordinate conversion and image optimization processing to obtain an underwater target imaging result. B up (k,θ i ) with B down (k,θ i ); k = 1,2,...,K; i = -N,-N+1,...,N-1; where k is the frequency point, θ i represents the angle corresponding to the i-th beam of the receiving array.

8. A wide-swath angular scanning imaging method according to claim 7, wherein, The frequency domain form of the output beam is Transforming the frequency domain form of the output beams of the upper and lower receive arrays to the time domain form, resulting in complex output sequences 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 Perform conjugate complex multiplication to compensate for the vertical pointing angle β of the transmitting transducer. m The complex output sequence b is obtained. 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= The output beam is subjected to double-array phase difference vertical direction estimation processing to determine the vertical direction corresponding to the output beam, which comprises: where * denotes complex conjugate, λ m is the center frequency of the mth element's transmitted pulse corresponding wavelength; performing a time domain smoothing operation on the complex output sequence b z (i,t n ) to calculate a complex amplitude angle; the complex amplitude angle is where arg[] denotes the argument operation, h(t n ) is a smoothing window function. transforming the complex argument φ'(i, t n ) to a vertical azimuth angle -N, -N+1,..., N-1; The vertical azimuth is where D is the vertical distance between the linear arrays, β m is the vertical pointing angle; Scattering points with a vertical direction angle exceeding the width of the transmitting beam are removed; The vertical orientation is wherein [·] is an integer operation, The vertical direction angle is discretized to determine the vertical direction; 9. The wide-swath angular scanning imaging method of claim 6, wherein, The unit angle of the divided grid is determined. The image array is subjected to noise suppression, coordinate conversion and image optimization processing, which comprises: The image array is subjected to noise suppression processing by a threshold method; The image array is subjected to spatial linear interpolation calculation to obtain an image in a three-dimensional rectangular coordinate system. The image in a three-dimensional orthogonal coordinate system is subjected to amplitude equalization, image filtering and / or sharpening processing.

10. A wide-angle scanning imaging system, characterized by, The application relates to a wide-angle scanning imaging device and a wide-angle scanning imaging method. The wide-angle scanning imaging device and the transceiving processing module of the wide-angle scanning imaging device execute the wide-angle scanning imaging method.

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