Method and apparatus for imaging using a multi-receiver synthetic aperture sonar considering intra-pulse motion

Abstract

The application discloses a multi-receiving array synthetic aperture sonar imaging method and device considering intrapulse motion, and comprises the following steps: under the condition that the relative motion speed of a platform in a signal transmitting and receiving pulse width is unchanged in a pulse repetition period, an echo baseband signal model in a two-dimensional plane is established; envelope time delay and phase of an echo baseband signal in the echo baseband signal model are error analyzed based on a waveform scaling factor, and an approximate signal model of the echo baseband signal model is determined; two-dimensional frequency spectrum of an approximate echo baseband signal in the approximate signal model is solved; and focusing is completed by using a single station imaging algorithm based on the two-dimensional frequency spectrum, so that a multi-receiving array synthetic aperture sonar imaging result is obtained. The application realizes multi-receiving array synthetic aperture sonar imaging under the condition of considering intrapulse motion, and improves the resolution of underwater imaging.

Description

Technical Field

[0001] This application relates to the field of underwater mapping, and more specifically, to a multi-receiver array synthetic aperture sonar imaging method and apparatus that takes into account intrapulse motion. Background Technology

[0002] Multi-subarray synthetic aperture sonar is widely used in seabed topographic mapping because its azimuth resolution is higher than that of side-scan sonar. The motion of the platform (i.e., the sonar platform) between transmitted and received pulses is called inter-pulse motion. Here, unlike the stop-go-stop model in synthetic aperture radar, inter-pulse motion in synthetic aperture sonar cannot be ignored; therefore, a non-stop-go-stop model is generally used in synthetic aperture sonar. The motion within the width of the transmitted and received pulses is called intra-pulse motion. When the platform moves at high speed or the pulse duration is long, intra-pulse motion cannot be ignored; it manifests as waveform stretching in the time domain.

[0003] Currently, in frequency-modulated continuous-wave synthetic aperture radar (FM-CMR) or high-altitude high-speed motion synthetic aperture radar (SAR) imaging, due to the long pulse duration and high platform speed, intrapulse motion is generally approximated as Doppler frequency shift. Furthermore, these approximations are based on the stop-go-stop model and are not applicable to sonar. Related research on the Doppler effect in multi-receiver array synthetic aperture sonar also relies on the stop-go-stop assumption and the backpropagation algorithm, without combining it with the frequency domain line-by-line algorithm. It also requires significant computational resources and cannot achieve real-time, high-resolution imaging considering intrapulse motion.

[0004] Therefore, providing a method for real-time, high-resolution multi-receiver array synthetic aperture sonar imaging that takes into account intrapulse motion has become an urgent problem to be solved. Summary of the Invention

[0005] To address at least one deficiency or improvement requirement of the prior art, the present invention provides a multi-receiver array synthetic aperture sonar imaging method and apparatus that takes into account intrapulse motion, thereby enabling the imaging method to be applicable to high-speed, large-pulse-width scenarios while ensuring high imaging resolution.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a multi-receiver array synthetic aperture sonar imaging method considering intra-pulse motion is provided. The method includes: establishing a two-dimensional echo baseband signal model within a two-dimensional plane, provided that the relative motion velocity of the platform within the pulse width of the transmitted and received signals remains constant during one pulse repetition period; performing error analysis on the envelope delay and phase of the echo baseband signal in the echo baseband signal model based on a waveform scaling factor to determine an approximate signal model of the echo baseband signal model; solving for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model; and using a single-station imaging algorithm to perform focusing based on the two-dimensional spectrum to obtain the multi-receiver array synthetic aperture sonar imaging result.

[0007] In an exemplary embodiment, establishing a two-dimensional echo baseband signal model while maintaining a constant relative velocity of the platform within the pulse width of the signal transmission and reception within a pulse repetition period includes: determining the relative velocity of the transmitting array in the multi-receiving array synthetic aperture sonar relative to the target as the relative velocity of the platform within the pulse width of the signal transmission and reception; determining the echo signal of each receiving array in the multi-receiving array synthetic aperture sonar based on the relative velocity; and demodulating the echo signal to remove the carrier frequency, thereby obtaining the echo baseband signal.

[0008] In an exemplary embodiment, determining the approximate signal model of the echo baseband signal model includes: obtaining a first analysis result by performing approximate error analysis on a first error factor, wherein the first error factor affects the envelope delay and phase of the echo signal; obtaining a second analysis result by performing approximate error analysis on a second error factor, wherein the second error factor affects the envelope delay of the echo signal; obtaining a third analysis result by performing approximate error analysis on a third error factor, wherein the third error factor affects the phase of the echo signal; and obtaining the approximate echo baseband signal based on the first analysis result, the second analysis result, and the third analysis result.

[0009] In an exemplary embodiment, solving for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model includes: obtaining the range frequency domain signal of the approximate echo baseband signal; and determining the range phase dwell time of the range frequency domain signal according to the phase dwell principle.

[0010] In an exemplary embodiment, after determining the range-direction phase dwell time of the range-frequency domain signal, the method further includes: determining the propagation time at the equivalent phase center as the signal propagation time of the approximate echo signal, determining the range history of the approximate echo baseband signal, and solving the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model based on the range history.

[0011] In an exemplary embodiment, the step of using a single-station imaging algorithm to perform focusing based on the two-dimensional spectrum to obtain the focusing result of multi-receiver array synthetic aperture sonar imaging includes: two-dimensional time-domain compensation of a fixed phase term in the two-dimensional spectrum, wherein the fixed phase term is a corresponding first phase multiplication factor; range compression after range-frequency Fourier transform using a second phase multiplication factor; and envelope delay compensation in the range-frequency domain using a third phase multiplication factor.

[0012] In an exemplary embodiment, the method further includes: obtaining the azimuth time-domain reconstruction result of the two-dimensional spectrum by inverse Fourier transform in the range frequency domain; and combining the azimuth time-domain reconstruction result with a single-station imaging algorithm to obtain the focusing result of the multi-receiver array synthetic aperture sonar imaging.

[0013] According to a second aspect of the present invention, a multi-receiver array synthetic aperture sonar imaging device considering intra-pulse motion is also provided, comprising: a modeling unit, configured to establish a two-dimensional echo baseband signal model in a plane, provided that the relative motion speed of the platform within the signal transmission and reception pulse width remains constant during one pulse repetition period; a first determining unit, configured to perform error analysis on the envelope delay and phase of the echo baseband signal in the echo baseband signal model based on a waveform scaling factor, and determine an approximate signal model of the echo baseband signal model; a first solving unit, configured to solve for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model; and an imaging unit, configured to perform focusing based on the two-dimensional spectrum using a single-station imaging algorithm to obtain the multi-receiver array synthetic aperture sonar imaging result.

[0014] According to a third aspect of the invention, a computer-readable storage medium is also provided, wherein a computer program is stored therein, wherein the computer program is configured to execute the above-described multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion at runtime.

[0015] According to a fourth aspect of the invention, an electronic device is also provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the above-described multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion via the computer program.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0017] (1) This invention provides a multi-receiver array synthetic aperture sonar imaging method considering intra-pulse motion. First, it considers the relative velocity of the platform within the pulse width of the transmitted and received signals, assuming that the relative velocity remains constant within one pulse repetition period, and establishes a two-dimensional echo baseband signal model considering intra-pulse motion. Based on this, the influence of relative velocity (waveform scaling factor) on the signal model's time delay and phase is analyzed. Through error analysis, a certain approximation is made to the model to facilitate subsequent processing. Using the dwell phase principle and employing the distance history under the phase center approximation, the two-dimensional spectrum of the approximated echo baseband signal is solved. The envelope shift and phase error caused by the micro-range migration resulting from the phase center approximation distance history are corrected, and focusing can be achieved by combining this with a single-station imaging algorithm.

[0018] (2) The multi-receiver array synthetic aperture sonar imaging method considering intra-pulse motion provided by this invention has an echo baseband signal model that considers intra-pulse motion, which is more accurate than the current non-stop-go-stop model and can be applied to high-speed, large pulse width and other situations. Within the allowable error range, the influence of intra-pulse motion on signal envelope and phase is analyzed, rather than simply approximating intra-pulse motion as frequency shift, so it is more accurate. The distance history based on phase center approximation is adopted, and the two-dimensional spectrum obtained by using the phase dwell principle is completely analytical. Any frequency domain line-by-line imaging algorithm can be combined with the obtained two-dimensional spectrum, which has universal applicability. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic flowchart of an optional multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion is provided for an embodiment of this application.

[0021] Figure 2 A schematic diagram illustrating the positional relationship between an optional synthetic aperture sonar transmitting array and a receiving array, provided for an embodiment of this application;

[0022] Figure 3(a) is a schematic diagram of an optional first error factor provided in an embodiment of this application;

[0023] Figure 3(b) is a schematic diagram of another optional first error factor provided in the embodiments of this application;

[0024] Figure 4 A schematic diagram illustrating an optional second error factor provided for an embodiment of this application;

[0025] Figure 5 A schematic diagram illustrating an optional third error factor provided for an embodiment of this application;

[0026] Figure 6 A schematic flowchart of an optional multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion is provided for an embodiment of this application.

[0027] Figure 7 A schematic diagram of point target focusing results for an optional multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion, provided as an embodiment of this application;

[0028] Figure 8 A schematic diagram of an optional multi-receiver array synthetic aperture sonar imaging device considering intrapulse motion, provided for an embodiment of this application;

[0029] Figure 9 This is a schematic diagram of an optional electronic device provided in an embodiment of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] The terms "first," "second," "third," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0032] According to one aspect of the embodiments of this application, a multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion is provided. The following is in conjunction with... Figure 1 This application describes a multi-receiver array synthetic aperture sonar imaging method that takes into account intrapulse motion, as provided in the embodiments of this application.

[0033] Figure 1 This is a schematic flowchart of an optional multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion, provided in an embodiment of this application. Figure 1 As shown, the process includes the following steps:

[0034] S102, under the condition that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception pulses during one pulse repetition cycle, establish a two-dimensional plane echo baseband signal model;

[0035] S104, Based on the waveform scaling factor, perform error analysis on the envelope delay and phase of the echo baseband signal in the echo baseband signal model to determine the approximate signal model of the echo baseband signal model;

[0036] S106, Solve for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model;

[0037] S108, based on two-dimensional spectrum, uses a single-station imaging algorithm to achieve focusing and obtain multi-receiver array synthetic aperture sonar imaging results.

[0038] The positional changes of the platform that occur within the time span of a single pulse transmission and reception are commonly referred to as intra-pulse motion. This motion has a significant impact on image quality because it causes envelope delay and phase changes in the echo signal, thereby affecting image resolution.

[0039] The multi-receiver array synthetic aperture sonar imaging algorithm provided in this application is applicable to scenarios with large pulse width and high platform speed, taking into account intrapulse motion. Using this method, more accurate imaging of underwater terrain or targets can be achieved.

[0040] In this embodiment, the relative motion velocity of the platform within the pulse width of signal transmission and reception is considered, and it is assumed that the relative motion velocity remains constant within one pulse repetition period. A two-dimensional echo baseband signal model considering intra-pulse motion is established. Based on this model, the influence of relative motion velocity (waveform scaling factor) on the envelope delay and phase of the signal model is analyzed. Through error analysis, certain approximations are made to the model to facilitate subsequent processing. Using the dwell phase principle and the distance history under the phase center approximation, the two-dimensional spectrum of the approximate echo baseband signal is solved, and the envelope offset and phase error caused by the micro-range migration due to the phase center approximation distance history are corrected. Finally, focusing is completed by combining with a single-station imaging algorithm.

[0041] When establishing the simulation model, the simulation can be performed according to the parameters recorded in Table 1, which is the simulation system parameter table.

[0042] Table 1

[0043]

[0044]

[0045] For example, Figure 2A schematic diagram illustrating the positional relationship between an optional synthetic aperture sonar transmitting array and a receiving array, as provided in an embodiment of this application, is shown below. Figure 2 As shown, Synthetic Aperture Sonar (SAS) is an advanced high-resolution underwater imaging technique that utilizes multiple receiver arrays to improve mapping speed. The SAS transmits a linear frequency modulated (LFM) signal, and the radial velocity between the SAS and the target P (the underwater mapping target) is v. r (t; r), the target's scattering intensity is A0; let f c K is the center frequency of the transmitted pulse signal. r The frequency modulation slope of the transmitted pulse signal; w r (·) represents the envelope of the transmitted pulse signal; w a (·) represents the antenna pattern weighting; A0 represents the amplitude. Unless otherwise specified, the amplitude term, which is irrelevant to imaging quality, is ignored in the formula derivation in this application.

[0046] Optionally, assuming the relative velocity between the platform and the target remains constant within one pulse repetition cycle, for ease of processing, the relative velocity of the transmitting array relative to the target is generally taken, allowing the establishment of a two-dimensional echo baseband signal model. After determining the echo baseband signal model, the waveform scaling factor can be determined based on the relative velocity, and error analysis can be performed on the envelope delay and phase of the echo baseband signal in the model. Based on the accurate signal model, an approximate signal model is obtained by simplification within the allowable error range. Then, the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model is solved, and focusing is completed by combining the two-dimensional spectrum with a single-station imaging algorithm, obtaining the focusing result of multi-receiver array synthetic aperture sonar imaging, thus realizing multi-receiver array synthetic aperture sonar imaging.

[0047] Through steps S102 to S108, a two-dimensional echo baseband signal model is established by ensuring that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception within one pulse repetition cycle. Error analysis is performed on the envelope delay and phase of the echo baseband signal in the model based on the waveform scaling factor to determine the approximate signal model. The two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model is solved. Based on the two-dimensional spectrum, focusing is completed using a single-station imaging algorithm to obtain the multi-receiver array synthetic aperture sonar imaging results. The echo baseband signal model considering intra-pulse motion is more accurate than the current non-stop-go-stop model and is applicable to high-speed, large-pulse-width scenarios. Within the allowable error range, the influence of intra-pulse motion on the signal envelope and phase is analyzed, rather than simply approximating intra-pulse motion as a frequency shift, thus making it more accurate. A distance history based on the phase center approximation is adopted, and the two-dimensional spectrum obtained using the phase dwell principle is completely analytical. Any frequency domain line-by-line imaging algorithm can be combined with the obtained two-dimensional spectrum, demonstrating universal applicability.

[0048] In an exemplary embodiment, establishing a two-dimensional echo baseband signal model within a pulse repetition cycle, assuming the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception, includes:

[0049] S11, the relative velocity of the transmitting array relative to the target in the multi-receiving array synthetic aperture sonar is determined as the relative motion velocity of the platform within the signal transmission and reception pulse width;

[0050] S12, Determine the echo signal of each receiver array in the multi-receiver array synthetic aperture sonar based on the relative velocity;

[0051] S13 demodulates the echo signal to remove the carrier frequency, obtaining the echo baseband signal.

[0052] In this embodiment, assuming the time delay difference between signals received at different positions within a single hydrophone array is negligible, the relative velocity of the transmitting array relative to the target in the multi-receiving array synthetic aperture sonar can be determined as the relative motion velocity of the platform within the signal transmission and reception pulse widths. Based on this relative velocity, the echo signal of each receiving array in the multi-receiving array synthetic aperture sonar is determined. For example, in a continuous motion state, the echo signal of the m-th receiving array can be expressed as:

[0053]

[0054] In the formula, Represents the waveform scaling factor (relative velocity). c represents the signal propagation time; v represents the underwater speed of sound; r (t) represents the radial velocity during pulse transmission and reception, f c K is the carrier frequency for the transmitted pulse signal. r τ is the frequency modulation slope for transmitting the Chirp signal; τ and t represent the slow time and fast time, respectively; A0 is the amplitude. Unless otherwise specified, the amplitude term, which is irrelevant to image quality, is ignored in the following formula derivation.

[0055] w r (·) represents the envelope of the transmitted pulse signal, which is approximately rectangular, and its expression can be: w r (τ)=rect(τ / T p ).

[0056] w a (·) is the two-way pattern weighting function for the transceiver array, and its expression can be:

[0057]

[0058] After demodulating the original echo signal and removing the carrier frequency, the expression for the demodulated echo baseband signal can be:

[0059]

[0060] Besides affecting the envelope delay and phase of the signal, the scaling factor *s* also causes changes in the frequency modulation slope and pulse width of the echo signal, which are reflected in the time domain as waveform stretching or compression. The imaging process is essentially a matched filter for the demodulated echo signal, allowing for analysis of the demodulated baseband echo signal. Changes in the frequency modulation slope lead to filter mismatch, causing the main lobe width (IRW) to widen and the side lobes to rise.

[0061] Optionally, for pulse signals, the IRW size can be determined using a 4dB beamwidth, and the quadratic phase error (QPE) can be used to quantitatively analyze the IRW broadening. This is done when the frequency modulation slope offset is ΔK and the pulse width is T. p When the pulse center is defined as the reference origin, the QPE mismatch is greatest at both ends of the pulse width, and QPE can be expressed as:

[0062]

[0063] Generally, when the IRW broadens by 2%, 5%, and 10%, the corresponding QPEs are 0.27π, 0.41π, and 0.55π, respectively. Since the broadening of the main lobe may cause the nearest sidelobe to fuse into the main lobe when the QPE is around 0.28π, we can use whether the QPE exceeds 0.27π as a criterion for whether to consider the effect of the scaling factor on the frequency modulation slope. In this case, the corresponding IRW broadening is 2%. Simulations using the parameters in Table 1 show a QPE of 0.018π, which is much smaller than 0.27π. Therefore, the effect of the scaling factor s on the frequency modulation slope can be ignored, but its effects on phase and time delay cannot be ignored. Furthermore, the phase in the echo baseband signal expression can be:

[0064]

[0065] In the formula:

[0066] τ 1,m (t;r) considers the influence of radial velocity on the traditional non-stop-go-stop time, which will change the signal delay and phase, τ 2,m (t;r) only affects latency, τ 3,m (t; r) will change the signal phase. To facilitate subsequent azimuth-to-Fourier transform, τ can be adjusted. 1,m (t;r), τ 2,m (t;r) and τ 3,m Simplify (t;r).

[0067] In one exemplary embodiment, determining an approximate signal model for the echo baseband signal model includes:

[0068] S21, by performing approximate error analysis on the first error factor, a first analysis result is obtained, wherein the first error factor affects the envelope delay and phase of the echo signal;

[0069] S22, by performing approximate error analysis on the second error factor, a second analysis result is obtained, wherein the second error factor affects the envelope delay of the echo signal;

[0070] S23, by performing approximate error analysis on the third error factor, the third analysis result is obtained, wherein the third error factor affects the phase of the echo signal;

[0071] S24. Based on the first analysis result, the second analysis result and the third analysis result, the approximate echo baseband signal is obtained.

[0072] In this embodiment, since the obtained echo baseband signal expression is complex and not conducive to subsequent processing, it can be approximated within the allowable error range, considering the influence of the radial velocity of the pulse motion on the signal transmission and reception time expression. In an optional example, by adjusting the first error factor (e.g., τ) 1,m An approximate error analysis is performed on (t;r) to obtain the first analysis result. Here, the first error factor affects the envelope delay and phase of the echo signal. By adjusting the second error factor (e.g., τ) 2,m An approximate error analysis is performed on (t;r) to obtain the second analysis result. Here, the second error factor affects the envelope delay of the echo signal; by adjusting the third error factor (e.g., τ) 3,m An approximate error analysis is performed on (t;r) to obtain the third analysis result. Here, the third error factor affects the phase of the echo signal. The approximate error analysis of the three error factors is performed in detail below.

[0073] 1)τ 1,m (t;r) Approximate Error Analysis

[0074]

[0075] If the radial velocity of the transmitting array is used, and assuming the pulse transmission and reception period v r (t)=v·sinθ T Unchanged, according to Figure 2 have The analytical expression for vr(t) can be obtained as follows:

[0076]

[0077] Will Expanding into linear terms of t, we can obtain τ. 1,m The approximate expression for (t; r) is:

[0078]

[0079] Where, α1=v 2 / c 2 The above approximation will give τ 1,m The error introduced by (t; r) is measured in units of time, and this time error can be expressed as:

[0080]

[0081] The parameters shown in Table 1 can be used to adjust Δτ. 1,m Simulation is performed using (t;r), Δτ 1,m (t;r) reaches its maximum value Δτ at the beam edge. 1,max,m (r), therefore, Δτ of different subarrays can be obtained. 1,max,m The variation pattern of (r) within the entire mapping zone is shown in Figures 3(a) and 3(b). It can be seen that c·Δτ exists throughout the entire mapping zone. 1，max，m (r) << λ / 8 and c·Δτ 1，max，m (r) << ρ r Therefore, τ 1,m (t;r) is represented as The resulting error is negligible.

[0082] 2)τ 2,m (t;r) Approximate Error Analysis

[0083] τ 2,m The expression for (t; r) is quite complex, so we will use τ 2,m If (t; r) is expanded into a linear term of t, then τ 2,m (t;r) can be approximated as:

[0084] in, The total error introduced by the above approximation is:

[0085]

[0086] The parameters shown in Table 1 can be used to adjust Δτ. 2,m Simulation was performed using (t; r) to obtain the edge subarray. The pattern of change throughout the entire surveying zone, such as Figure 4 As shown. From Figure 4 It can be seen that the entire surveying area contains Therefore, τ 2,m (t;r) is represented as The resulting error is negligible.

[0087] 3)τ 3,m (t;r) Approximate Error Analysis

[0088] τ 3,m The expression for (t; r) is quite complex. If it is ignored, the resulting error is:

[0089] Δτ 3,m (t;r)=τ 3,m (t;r)

[0090] Based on the parameters shown in Table 1, Δτ 3,m Simulation was performed using (t; r) to obtain the edge subarray. The pattern of change throughout the entire surveying zone, such as Figure 5 As shown. From Figure 5 It can be seen that the entire surveying area contains Ignore τ 3,m The phase error caused by (t; r) is negligible.

[0091] After obtaining the above error analysis results, an approximate form of the echo baseband signal can be established. After the above three approximations, the baseband form of the echo signal received by the m-th receiving array at the target P(r,0) can be expressed as:

[0092]

[0093] Let f c K is the center frequency of the transmitted pulse signal. r The frequency modulation slope of the transmitted pulse signal; w r (·) represents the envelope of the transmitted pulse signal; w a (·) represents the antenna pattern weighting; A0 represents the amplitude. Unless otherwise specified, the amplitude term, which is irrelevant to image quality, is ignored in the subsequent formula derivation. Therefore, the baseband form of the echo signal received by the m-th receiving array from the target P located at (r,0) can be expressed as:

[0094]

[0095] In one exemplary embodiment, solving for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model includes:

[0096] S31, obtain the range-frequency domain signal of the approximate echo baseband signal;

[0097] S32, based on the phase dwell principle, determine the range-direction phase dwell time of the range frequency domain signal.

[0098] In this embodiment of the application, the expression for the obtained range-frequency domain signal is:

[0099]

[0100] The phase in the range frequency domain signal expression is:

[0101]

[0102] According to the phase dwell principle, let The range-direction phase dwell time can be obtained as follows:

[0103]

[0104] Furthermore, τ can be PSP,m (f r ,t;r) Substitute From:

[0105]

[0106] In one exemplary embodiment, after determining the range-direction phase dwell time of the range frequency domain signal, the method further includes:

[0107] S41, the propagation time at the equivalent phase center is determined as the signal propagation time of the approximate echo signal, and the distance history of the approximate echo baseband signal is determined;

[0108] S42, based on distance history, solves the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model.

[0109] In the embodiments of this application, using Figure 2 The propagation time corresponding to the effective phase center (EPC) in the middle is replaced by Therefore, distance history can be represented as:

[0110]

[0111] In the formula ΔR m (r) represents micro-distance migration, and its expression can be:

[0112] ΔR m (r)=(2vr / c+d m ) 2 / (4r)

[0113] Furthermore, an orientation Fourier transform is performed to obtain...

[0114]

[0115] According to the phase dwell principle, let The range-direction phase dwell time can be obtained as follows:

[0116]

[0117] In the formula:

[0118] t PSP,m (f r ,f a ;r) Substitute In the middle, then D 2df Expand to f r The quadratic term, then It can be represented as:

[0119]

[0120] Among them, the following conditions must be met:

[0121]

[0122] The first term in the expression is the azimuth modulation term; the second term is the effect of stop-and-go communication; the first two terms can be compensated for by azimuth compression in range Doppler. The third term is the transmit signal modulation term, which is the source of range pulse compression; the fourth term is the linear phase term of the Doppler frequency caused by the separate transmit and receive signals, which can be compensated for by azimuth frequency domain reconstruction or time domain reconstruction; the fifth term is the second-order coupling term of range and azimuth, which needs to be compensated for by second-order range compression; the sixth term is the linear phase term of the range frequency, corresponding to range cell migration (RCM), which will cause envelope offset and needs to be compensated for by time delay correction; the seventh term is the linear phase of the carrier, which will change the phase of the signal and needs to be compensated for by phase correction before azimuth reconstruction. If we let α1 = 0 and α2 = 0, then... This will degenerate into a traditional two-dimensional spectrum, which also explains why, at high speeds, additional envelope shifts and phase changes determined by α1 and α2 will occur.

[0123] In one exemplary embodiment, focusing is achieved by combining two-dimensional spectrum and a single-station imaging algorithm to obtain multi-receiver array synthetic aperture sonar imaging results, including:

[0124] S51, a two-dimensional time-domain compensation fixed phase term in a two-dimensional spectrum, wherein the fixed phase term is the corresponding first phase multiplication factor;

[0125] S52, distance compression is performed after the Fourier transform in the distance frequency domain by using the second phase multiplication factor;

[0126] S53 performs envelope delay compensation in the distance frequency domain through a third phase multiplication factor.

[0127] In the embodiments of this application, such as Figure 6As shown, FFT stands for Fast Fourier Transform; IFFT stands for Inverse Fast Fourier Transform. The invention will be further described below with reference to the accompanying drawings and embodiments. Based on the aforementioned two-dimensional spectrum, each subarray eliminates ΔR through micro-distance migration. m The envelope shift and phase error introduced by (r) are first compensated for in the two-dimensional time domain by fixing the phase term. The corresponding phase multiplication factor (first phase multiplication factor) is:

[0128]

[0129] Then, after the range-frequency Fourier transform, range compression is performed, and the phase multiplication factor (second phase multiplication factor) is:

[0130]

[0131] In the distance frequency domain, envelope delay compensation is performed, and the corresponding phase multiplication factor (third phase multiplication factor) is:

[0132]

[0133] In the above formula: r c α is the center distance of the surveying zone. 2,ref For in r c The value at that location.

[0134] In one exemplary embodiment, the above method further includes:

[0135] S61, by performing an inverse Fourier transform in the distance frequency domain, the azimuth time domain reconstruction result of the two-dimensional spectrum is obtained;

[0136] S62, combining the azimuth time-domain reconstruction results with the single-station imaging algorithm, yields multi-receiver array synthetic aperture sonar imaging results.

[0137] In this embodiment, the terms related to the array element number in the signal have been eliminated, meaning the conversion from a multi-subarray signal to a single-array signal has been completed. Focusing can then be achieved using a traditional monostation imaging algorithm. For example, the focusing result obtained using the range-Doppler algorithm is shown below. Figure 6 As shown. By performing an inverse Fourier transform in the range frequency domain, the azimuth time-domain reconstruction result of the two-dimensional spectrum is obtained. Combining the azimuth time-domain reconstruction result with the single-station imaging algorithm, the focusing result of the multi-receiver array synthetic aperture sonar (i.e., the imaging result) is obtained.

[0138] According to another aspect of the embodiments of this application, an imaging apparatus for implementing the above-described multi-receiver array synthetic aperture sonar imaging method that takes into account intrapulse motion is also provided. Figure 8 This is a schematic diagram of an optional multi-receiver array synthetic aperture sonar imaging device considering intrapulse motion according to an embodiment of this application, as shown below. Figure 8As shown, the device may include:

[0139] Unit 802 is used to establish a two-dimensional echo baseband signal model in a plane, provided that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception pulses during one pulse repetition cycle.

[0140] The first determining unit 804 is used to perform error analysis on the envelope delay and phase of the echo baseband signal in the echo baseband signal model based on the waveform scaling factor, and to determine the approximate signal model of the echo baseband signal model.

[0141] The first solving unit 806 is used to solve the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model;

[0142] The imaging unit 808 is used to focus based on the two-dimensional spectrum using a single-station imaging algorithm to obtain multi-receiver array synthetic aperture sonar imaging results.

[0143] It should be noted that the establishment unit 802 in this embodiment can be used to perform the above step S102, the first determination unit 804 in this embodiment can be used to perform the above step S104, the first solution unit 806 in this embodiment can be used to perform the above step S106, and the imaging unit 808 in this embodiment can be used to perform the above step S108.

[0144] Through the above modules, a two-dimensional echo baseband signal model is established by ensuring that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception within one pulse repetition cycle. Error analysis is performed on the envelope delay and phase of the echo baseband signal in the model based on waveform scaling factors to determine the approximate signal model. The two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model is solved. Based on the two-dimensional spectrum, focusing is achieved using a single-station imaging algorithm to obtain the multi-receiver array synthetic aperture sonar imaging results. The echo baseband signal model considering intra-pulse motion is more accurate than the current non-stop-go-stop model and is applicable to high-speed, large-pulse-width scenarios. Within the allowable error range, the influence of intra-pulse motion on the signal envelope and phase is analyzed, rather than simply approximating intra-pulse motion as a frequency shift, thus achieving greater accuracy. A distance history based on phase center approximation is adopted, and the two-dimensional spectrum obtained using the phase dwell principle is completely analytical. Any frequency domain line-by-line imaging algorithm can be combined with the obtained two-dimensional spectrum, demonstrating universal applicability.

[0145] In one exemplary embodiment, the establishment unit includes:

[0146] The first determining module is used to determine the relative velocity of the transmitting array relative to the target in the multi-receiving array synthetic aperture sonar as the relative motion velocity of the platform within the signal transmission and reception pulse width;

[0147] The second determining module is used to determine the echo signal of each receiving array in the multi-receiving array synthetic aperture sonar based on the relative velocity;

[0148] The echo signal is demodulated and the carrier frequency is removed to obtain the echo baseband signal.

[0149] In one exemplary embodiment, the determining unit includes:

[0150] The first analysis module is used to obtain a first analysis result by performing approximate error analysis on a first error factor, wherein the first error factor affects the envelope delay and phase of the echo signal;

[0151] The second analysis module is used to obtain a second analysis result by performing approximate error analysis on the second error factor, wherein the second error factor affects the envelope delay of the echo signal;

[0152] The third analysis module is used to obtain a third analysis result by performing approximate error analysis on a third error factor, wherein the third error factor affects the phase of the echo signal;

[0153] An approximation module is used to obtain the approximate echo baseband signal based on the first analysis result, the second analysis result, and the third analysis result.

[0154] In one exemplary embodiment, the solving unit includes:

[0155] The acquisition module is used to acquire the range-frequency domain signal of the approximate echo baseband signal;

[0156] The third determining module is used to determine the range-direction phase dwell time of the range frequency domain signal based on the phase dwell principle.

[0157] In one exemplary embodiment, the apparatus further includes:

[0158] The second determining unit is used to determine the propagation time at the equivalent phase center as the signal propagation time of the approximate echo signal, and to determine the distance history of the approximate echo baseband signal;

[0159] The second solving unit is used to solve the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model based on the distance history.

[0160] In one exemplary embodiment, the imaging includes:

[0161] The first compensation module is used to compensate for a fixed phase term in the two-dimensional time domain of the two-dimensional spectrum, wherein the fixed phase term is a corresponding first phase multiplication factor;

[0162] The compression module is used to perform distance compression after the Fourier transform in the distance frequency domain using a second phase multiplication factor;

[0163] The second compensation module is used to perform envelope delay compensation in the distance frequency domain by using the third phase multiplication factor.

[0164] In one exemplary embodiment, the apparatus further includes:

[0165] The reconstruction unit is used to obtain the azimuth time-domain reconstruction result of the two-dimensional spectrum through the inverse Fourier transform in the distance frequency domain;

[0166] The focusing unit is used to combine the azimuth time-domain reconstruction result with the single-station imaging algorithm to obtain the multi-receiver array synthetic aperture sonar imaging result.

[0167] It should be noted that the examples and scenarios implemented by the above modules and corresponding steps are the same, but are not limited to the content disclosed in the above embodiments. It should be noted that the above modules, as part of the device, can run in a hardware environment, and can be implemented by software or hardware. The hardware environment includes a network environment.

[0168] According to another aspect of the embodiments of this application, a storage medium is also provided. Optionally, in this embodiment, the storage medium can be used to execute program code of any of the multi-receiver array synthetic aperture sonar imaging methods considering intrapulse motion described above in the embodiments of this application.

[0169] Optionally, in this embodiment, the storage medium is configured to store program code for performing the following steps:

[0170] S1. Under the condition that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception pulses during one pulse repetition cycle, establish a two-dimensional plane echo baseband signal model.

[0171] S2, Based on the waveform scaling factor, error analysis is performed on the envelope delay and phase of the echo baseband signal in the echo baseband signal model to determine the approximate signal model of the echo baseband signal model;

[0172] S3, Solve for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model;

[0173] S4, based on the two-dimensional spectrum, uses a single-station imaging algorithm to complete focusing and obtain multi-receiver array synthetic aperture sonar imaging results.

[0174] Optionally, specific examples in this embodiment can refer to the examples described in the above embodiments, and will not be repeated in this embodiment.

[0175] The computer-readable storage medium may include, but is not limited to, any type of disk, including floppy disks, optical disks, DVDs, CD-ROMs, microdrives, as well as magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, DRAMs, VRAMs, flash memory devices, magnetic cards or optical cards, nanosystems (including molecular memory ICs), or any type of medium or device suitable for storing instructions and / or data.

[0176] According to another aspect of the embodiments of this application, an electronic device is also provided for implementing the above-described multi-receiver array synthetic aperture sonar imaging method that takes into account intrapulse motion. The electronic device may be a server, a terminal, or a combination thereof.

[0177] Figure 9 This is a schematic diagram of the structure of an optional electronic device according to an embodiment of this application, such as... Figure 9 As shown, it includes a processor 902, a communication interface 904, a memory 906, and a communication bus 908. The processor 902, communication interface 904, and memory 906 communicate with each other via the communication bus 908.

[0178] Memory 906 is used to store computer programs;

[0179] When processor 902 executes a computer program stored in memory 906, it performs the following steps:

[0180] S1. Under the condition that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception pulses during one pulse repetition cycle, establish a two-dimensional plane echo baseband signal model.

[0181] S2, Based on the waveform scaling factor, error analysis is performed on the time delay and phase of the echo baseband signal in the echo baseband signal model to determine the approximate signal model of the echo baseband signal model;

[0182] S3, Solve for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model;

[0183] S4, based on the two-dimensional spectrum, uses a single-station imaging algorithm to complete focusing and obtain multi-receiver array synthetic aperture sonar imaging results.

[0184] Optionally, the communication bus can be a PCI (Peripheral Component Interconnect) bus or an EISA (Extended Industry Standard Architecture) bus, etc. This communication bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Figure 9The symbol is represented by a single thick line, but this does not indicate that there is only one bus or one type of bus. The communication interface is used for communication between the aforementioned electronic device and other devices.

[0185] The memory may include RAM, or non-volatile memory, such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0186] As an example, the memory 906 described above may include, but is not limited to, the establishment unit 802, the first determination unit 804, the first solution unit 806, and the imaging unit 808 in the multi-receiver array synthetic aperture sonar imaging device that considers intrapulse motion. Furthermore, it may include, but is not limited to, other module units in the multi-receiver array synthetic aperture sonar imaging device that considers intrapulse motion, which will not be elaborated upon in this example.

[0187] The processors mentioned above can be general-purpose processors, including but not limited to: CPU (Central Processing Unit), NP (Network Processor), etc.; they can also be DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0188] Optionally, specific examples in this embodiment can refer to the examples described in the above embodiments, and will not be repeated here.

[0189] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0190] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0191] In the several embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some service interface; the indirect coupling or communication connection between devices or units may be electrical or other forms.

[0192] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0193] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0194] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0195] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, which may include: a flash drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, etc.

[0196] The foregoing description is merely an exemplary embodiment of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Those skilled in the art will readily conceive of embodiments of this disclosure upon considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.

[0197] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0198] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion, characterized in that, include: Under the condition that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception pulses during one pulse repetition cycle, a two-dimensional echo baseband signal model is established; The waveform scaling factor is determined based on the relative motion velocity. Based on the waveform scaling factor, error analysis is performed on the envelope delay and phase of the echo baseband signal in the echo baseband signal model to determine the approximate signal model of the echo baseband signal model. Solve for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model; Based on the two-dimensional spectrum, focusing is completed using a single-station imaging algorithm to obtain multi-receiver array synthetic aperture sonar imaging results. The approximate signal model used to determine the echo baseband signal model includes: By performing approximate error analysis on the first error factor, a first analysis result is obtained, wherein the first error factor affects the envelope delay and phase of the echo signal; By performing approximate error analysis on the second error factor, a second analysis result is obtained, wherein the second error factor affects the envelope delay of the echo signal; By performing approximate error analysis on the third error factor, a third analysis result is obtained, wherein the third error factor affects the phase of the echo signal; Based on the first analysis result, the second analysis result, and the third analysis result, the approximate echo baseband signal is obtained; After three approximations, the first... m The receiver array receives data located at target P. The baseband form of the echo signal at that location is expressed as: in, , ;c represents the speed of sound underwater. The center frequency of the transmitted pulse signal; The frequency modulation slope of the transmitted pulse signal; For the envelope of the transmitted pulse signal; Weight the antenna pattern; For amplitude, and They represent slow time and fast time, respectively. This represents the signal propagation time.

2. The multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion as described in claim 1, characterized in that, The establishment of a two-dimensional echo baseband signal model, under the condition that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception within one pulse repetition cycle, includes: The relative velocity of the transmitting array relative to the target in a multi-receiving array synthetic aperture sonar is determined as the relative motion velocity of the platform within the signal transmission and reception pulse width; The echo signal of each receiver array in the multi-receiver array synthetic aperture sonar is determined based on the relative velocity. The echo signal is demodulated and the carrier frequency is removed to obtain the echo baseband signal.

3. The multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion as described in claim 1, characterized in that, The process of solving for the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model includes: Obtain the range-frequency domain signal of the approximate echo baseband signal; Based on the phase dwell principle, the range-direction phase dwell time of the range frequency domain signal is determined.

4. The multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion as described in claim 3, characterized in that, After determining the range-direction phase dwell time of the range frequency domain signal, the method further includes: The propagation time at the equivalent phase center is determined as the signal propagation time of the approximate echo signal, and the distance history of the approximate echo baseband signal is determined. Based on the distance history, the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model is solved.

5. The multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion as described in claim 1, characterized in that, The process of focusing based on the two-dimensional spectrum using a single-station imaging algorithm to obtain multi-receiver array synthetic aperture sonar imaging results includes: The two-dimensional time-domain compensated fixed-phase term in the two-dimensional spectrum, wherein the fixed-phase term is the corresponding first phase multiplication factor; Range compression is performed after the range frequency domain Fourier transform using the second phase multiplication factor; Envelope delay compensation is performed in the distance frequency domain using a third phase multiplication factor.

6. The multi-receiver array synthetic aperture sonar imaging method considering intrapulse motion as described in any one of claims 1-5, characterized in that, The method further includes: The azimuth time-domain reconstruction result of the two-dimensional spectrum is obtained by inverse Fourier transform in the distance frequency domain; The multi-receiver array synthetic aperture sonar imaging results are obtained by combining the azimuth time-domain reconstruction results with the single-station imaging algorithm.

7. A multi-receiver array synthetic aperture sonar imaging device considering intra-pulse motion, used to perform the multi-receiver array synthetic aperture sonar imaging method considering intra-pulse motion as described in claim 1, characterized in that, include: A modeling unit is established to create a two-dimensional echo baseband signal model in a plane, provided that the relative motion speed of the platform remains constant within the pulse width of the signal transmission and reception within one pulse repetition cycle. The first determining unit is used to perform error analysis on the envelope delay and phase of the echo baseband signal in the echo baseband signal model based on the waveform scaling factor, and to determine the approximate signal model of the echo baseband signal model. The first solving unit is used to solve the two-dimensional spectrum of the approximate echo baseband signal in the approximate signal model; The imaging unit is used to focus based on the two-dimensional spectrum using a single-station imaging algorithm to obtain multi-receiver array synthetic aperture sonar imaging results.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored program, wherein the program, when executed, performs the method of any one of claims 1 to 6.

9. An electronic device comprising a memory and a processor, characterized in that, The memory stores a computer program, and the processor is configured to execute the method of any one of claims 1 to 6 through the computer program.

Images