A synthetic aperture sonar echo simulation method and system
By calculating Doppler scale factor and frequency domain scale transformation, the calculation complexity is reduced, and the problem of low simulation efficiency in traditional synthetic aperture sonar in high-speed scenarios is solved, and efficient echo simulation and accurate imaging results are achieved.
Patent Information
- Application Number
- CN202410460541.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Priority Date
- 2024-03-11
- Filing Date
- 2024-04-17
- Publication Date
- 2024-12-20
- Estimated Expiration
- 2044-04-17
AI Technical Summary
Traditional synthetic aperture sonar cannot effectively simulate the Doppler effect phenomenon in transmitted signal pulses in high-speed scenarios, and the calculation cost of high-speed scene time domain echo algorithm based on point cloud model is too high to meet the high-speed operation requirements.
By calculating the Doppler scale factor of the target and the frequency-domain scale transformed frequency, the frequency-domain echo signal of the point target is calculated, and the frequency-domain echo signal of each target is superimposed and the distance is inverse Fourier transformed to obtain Time domain simulation echo signals reduce calculation complexity and improve simulation efficiency.
It greatly reduces the computational complexity, improves the echo simulation efficiency of high-speed scene synthetic aperture sonar, and can accurately simulate the echo signals in high-speed scenes without losing imaging performance.
Smart Images
Figure CN118350201B_ABST
Abstract
Description
Technical Field
[0001] The present application belongs to the field of image processing technology, and specifically relates to a synthetic aperture sonar echo simulation method and system. Background Art
[0002] Synthetic aperture sonar is a high-resolution imaging sonar widely used underwater. Its working principle is to transmit sound wave signals at different positions through the movement of a small aperture array platform and receive the signal echo reflected by the target, and perform coherent processing on the received signal to synthesize an equivalent large aperture, thereby achieving high-resolution imaging of the target. Considering the complexity of the synthetic aperture sonar system and the operating cost of the actual mission, the computer simulation method of echo data is of great significance in sonar parameter design, imaging algorithm testing and verification, image quality evaluation, motion error correction algorithm testing and verification, etc.
[0003] With the continuous development of related technologies, the operating speed of traditional synthetic aperture sonar can no longer meet the needs of some scenarios. As the demand for improving the operating speed of the system continues to increase, the traditional echo computer simulation method of the physical model of low-speed scenes cannot simulate the Doppler effect phenomenon in the transmitted signal pulse, and is therefore no longer suitable for high-speed scenes. At the same time, since the radial velocity of each target point in the scene is different at each spatial sampling, the Doppler history of each target point in the pulse is also different. The time domain echo algorithm for high-speed scenes based on the point cloud model has too high a computational cost when facing a large number of target points. Without optimizing the existing algorithm, it can only exchange the simulation computing efficiency at the expense of hardware cost. Summary of the invention
[0004] The purpose of this application is to overcome the defect that the operating speed of traditional synthetic aperture sonar can no longer meet the demand.
[0005] In order to achieve the above objectives, the present application proposes a synthetic aperture sonar echo simulation method, comprising:
[0006] Step S1. When the target is located within the azimuth beam opening angle of the synthetic aperture, the Doppler scale factor of the target and the frequency of the target after frequency domain scale transformation are calculated;
[0007] Step S2. Calculate the frequency domain echo signal of the point target;
[0008] Step S3. Calculate the echo signals of all targets in the imaging scene;
[0009] Step S4: superimpose the frequency domain echo signals of each target and perform inverse Fourier transform in the range direction to obtain a time domain simulation echo signal.
[0010] As an improvement of the above method, in step S1, the target is located within the azimuth beam opening angle of the synthetic aperture when the sonar operation position satisfies the following relationship:
[0011]
[0012] in, is the relative distance between the platform's operating position and the target's azimuth; r m is the target slant range; the subscripts m and n represent the mth target and the nth azimuth spatial sampling respectively; the superscript k represents the kth subarray; λ is the signal wavelength; and D is the array element aperture.
[0013] As an improvement of the above method, the calculation formula of the Doppler scale factor is:
[0014]
[0015] Where t represents the distance to the fast time; τ n represents the slow time of the nth sampling in azimuth; the mth target is located in the slant range-azimuth plane (r m ,y m ) at; α = v / c is the Doppler factor, that is, the ratio of the platform running speed to the speed of sound in water; It represents the incident angle of the sound ray between the kth subarray and the mth target under the nth azimuth sampling, which is obtained from the geometric relationship between the target and the array element; For The corresponding Doppler scale factor.
[0016] As an improvement of the above method, the frequency calculation formula after frequency domain scaling is:
[0017]
[0018] Among them, f r is the distance frequency; is the Doppler scale factor corresponding to the incident angle of the sound ray; f rd is the frequency after distance scale transformation.
[0019] As an improvement of the above method, in step S2, calculating the frequency domain echo signal of the point target includes:
[0020] Step S2.1 calculates the range spectrum window function of the frequency domain echo signal;
[0021] Step S2.2 calculates the secondary phase term of the frequency domain echo signal;
[0022] Step S2.3 calculates the time delay phase term of the frequency domain echo signal;
[0023] Step S2.4 calculates the echo frequency domain result.
[0024] As an improvement of the above method, the step S2.1 calculates the range spectrum window function of the frequency domain echo signal, and the calculation formula is as follows:
[0025]
[0026] in, represents the range spectrum window function of the frequency domain echo signal corresponding to the Doppler scale factor; f rd is the distance scale transformation frequency; f 0 is the carrier frequency; K r is the signal modulation frequency; T is the signal duration; rect(·) is the rectangular window function:
[0027]
[0028] Where x represents the rectangular window function parameter.
[0029] As an improvement of the above method, the step S2.2 calculates the secondary phase term of the frequency domain echo frequency domain signal, and the calculation formula is as follows:
[0030]
[0031] in, represents the secondary phase term of the frequency domain echo signal corresponding to the Doppler scale factor; j 2 =-1 is the imaginary unit; K r is the signal modulation frequency; f rd is the distance scale transformation frequency; f 0 is the carrier frequency.
[0032] As an improvement of the above method, step S2.3 calculates the time delay phase term of the frequency domain echo signal, and the calculation formula is as follows:
[0033]
[0034] in, represents the time delay phase term of the frequency domain echo signal corresponding to the Doppler scale factor; 2 =-1 is the imaginary unit; c is the speed of sound in water; f rd is the distance scale transformation frequency; is the equivalent phase center path under slow time scale, and its expression is:
[0035]
[0036] Among them, the point target is located in the slant range-azimuth plane (r m ,y m ) at the place; v represents the platform running speed; u kis the distance from the kth receiving array element to the transmitting array element; is the round-trip delay of the sending and receiving process determined according to the geometric relationship;
[0037] For the case of separate sending and receiving, Replaced with send and receive split sound path The calculation formula is:
[0038]
[0039] As an improvement of the above method, the step S2.4 calculates the echo frequency domain result, and the calculation formula is as follows:
[0040]
[0041] in, It represents the range frequency domain-azimuth time domain echo received by the kth subarray at the mth target and the nth azimuth spatial sampling; represents the distance spectrum window function; Represents the secondary phase term of the frequency domain echo signal; represents the time delay phase term of the frequency domain echo signal; f rd Represents the distance scale transformation frequency.
[0042] As an improvement of the above method, in step S4, the frequency domain echo signals of each target are superimposed and then inverse Fourier transform is performed in the range direction to obtain a time domain simulation echo signal, and the calculation formula is:
[0043]
[0044] in, It represents the echo signal of the range time domain-azimuth time domain received by the kth subarray at the nth azimuth spatial sampling; Represents the frequency of distance scale transformation f t Perform inverse Fourier transform; It represents the range frequency domain-azimuth time domain echo received by the kth subarray for the mth target and the nth azimuth spatial sampling; m = 1, 2, ..., N p is the target ordinal number; f rd is the range scale transformation frequency; the mth target is located in the slant range-azimuth plane (r m ,y m ) at the point; t represents the distance to the fast time; τ n Indicates the slow time of the nth sampling in the azimuth direction.
[0045] The present application also provides a synthetic aperture sonar echo simulation system, which is implemented based on the above method, and the system includes:
[0046] A module for calculating the Doppler scale factor of a target and the frequency of a target after frequency domain scaling, which is used to calculate the Doppler scale factor of a target and the frequency of a target after frequency domain scaling when the target is located within the azimuth beam opening angle of a synthetic aperture;
[0047] A frequency domain echo signal calculation module is used to calculate the frequency domain echo signal of a point target;
[0048] An echo signal calculation module, used for calculating echo signals of all targets in the imaging scene; and
[0049] The module for calculating the time domain simulated echo signal is used to superimpose the frequency domain echo signals of each target and then perform inverse Fourier transform in the range direction to obtain the time domain simulated echo signal.
[0050] Compared with the prior art, the advantages of this application are:
[0051] The synthetic aperture sonar echo simulation method provided in the present application greatly reduces the computational complexity by performing fast time-scale delay processing in the frequency domain approximating the time domain through frequency domain scaling transformation, thereby improving the echo simulation efficiency of the synthetic aperture sonar in high-speed scenes. BRIEF DESCRIPTION OF THE DRAWINGS
[0052] Figure 1 Shown is a processing flow chart of a synthetic aperture sonar echo simulation method;
[0053] Figure 2 Shown is a graph comparing echo simulation durations in the embodiment;
[0054] Figure 3 Shown is a simulated echo graph in the embodiment;
[0055] Figure 4 The figure shows the imaging result of the simulated echo in the embodiment;
[0056] Figure 5 The figure shows the result of the high-speed scene time domain method simulation echo imaging;
[0057] Figure 6 The figure shows a -6dB profile comparison of the simulated echo in the embodiment and the simulated echo imaging result of the high-speed scene time domain method;
[0058] Figure 7 Shown is the result of simulating echo imaging using the time domain method for a low-speed scene. DETAILED DESCRIPTION
[0059] The technical solution of the present application is described in detail below with reference to the accompanying drawings.
[0060] The present invention provides a method and system for simulating the echo of synthetic aperture sonar, which is based on frequency domain scaling, and greatly reduces the computational complexity by approximating the fast time scale delay processing of the time domain in the frequency domain through the frequency domain scaling, thereby improving the echo simulation efficiency of the synthetic aperture sonar in high-speed scenes.
[0061] Example 1
[0062] like Figure 1 As shown, this embodiment provides a synthetic aperture sonar echo simulation method, comprising the following steps:
[0063] S1. When the target is within the azimuth beam opening angle of the synthetic aperture of the sonar, calculate the Doppler scale factor, the calculation formula is as follows:
[0064]
[0065] Where t represents the distance to the fast time; τ n represents the slow time of the nth sampling in azimuth; the mth target is located in the slant range-azimuth plane (r m ,y m ) at; α = v / c is the Doppler factor, that is, the ratio of the platform running speed to the speed of sound in water; It represents the incident angle of the sound ray between the kth subarray and the mth target under the nth azimuth sampling, which can be obtained from the geometric relationship between the target and the array element; For The corresponding Doppler scale factor. At the same time, the equivalent phase center path under the slow time scale is calculated Its expression is:
[0066]
[0067] Among them, the point target is located in the slant range-azimuth plane (r m ,y m ) k is the distance from the kth receiving array element to the transmitting array element; It is the round-trip delay of the sending and receiving process determined according to the geometric relationship.
[0068] S2. When the target is within the azimuth beam opening angle of the synthetic aperture, the frequency of the target after frequency domain scaling is calculated. The calculation formula is:
[0069]
[0070] Among them, f r is the distance frequency; For The corresponding Doppler scale factor; f rd is the distance scale transformation frequency.
[0071] S3. Calculating the frequency domain echo signal of the point target further comprises:
[0072] S3.1. Calculate the range spectrum window function of the frequency domain echo signal. The calculation formula is as follows:
[0073]
[0074] in, Representation and The corresponding range spectrum window function of the frequency domain echo signal; f rd is the distance scale transformation frequency; f 0 is the carrier frequency; K r is the signal modulation frequency; T is the signal duration; rect(·) is the rectangular window function, defined as:
[0075]
[0076] S3.2. Calculate the secondary phase term of the frequency domain echo frequency domain signal. The calculation formula is as follows:
[0077]
[0078] Representation and The corresponding secondary phase term of the frequency domain echo signal; 2 =-1 is the imaginary unit; K r is the signal modulation frequency; f rd is the distance scale transformation frequency; f 0 is the carrier frequency.
[0079] S3.3. Calculate the time delay phase term of the frequency domain echo signal. The calculation formula is as follows:
[0080]
[0081] Representation and The corresponding delay phase term of the frequency domain echo signal; 2 =-1 is the imaginary unit; c is the speed of sound in water; f rd is the distance scale transformation frequency; is the equivalent phase center acoustic path at a slow time scale.
[0082] S3.4. Calculate the echo frequency domain result. The calculation formula is as follows:
[0083]
[0084] in, It represents the range frequency domain-azimuth time domain echo received by the kth subarray at the mth target and the nth azimuth spatial sampling; represents the distance spectrum window function; Represents the secondary phase term of the frequency domain echo signal; Represents the time delay phase term of the frequency domain echo signal.
[0085] S4. Superimpose the frequency domain echo signals of each target and perform inverse Fourier transform in the range direction to obtain the time domain simulation echo signal. The calculation formula is:
[0086]
[0087] in, It represents the echo signal of the range time domain-azimuth time domain received by the kth subarray at the nth azimuth spatial sampling; Represents the frequency of distance scale transformation f t Perform inverse Fourier transform; It represents the range frequency domain-azimuth time domain echo received by the kth subarray for the mth target and the nth azimuth spatial sampling; m = 1, 2, ..., N p is the target ordinal number, .
[0088] If the single subarray echo matrix Size is N a ×N r . Then when the number of targets is N p When the floating point operations (FLOPs) of the high-speed scene time domain algorithm are approximately:
[0089] Q time ≈2×N p ×15N r ×N a
[0090] The floating point calculation amount of the method provided by the present invention is approximately:
[0091] Q F ≈2×N p ×(8N r +10)×N a +N a ×5N r log 2 N r
[0092] The overall technical process of the present invention is shown in Table 1:
[0093] Table 1 Synthetic aperture sonar echo simulation method flow
[0094]
[0095]
[0096] Consider the presence of 1, 10, 10 2 10 3 10 4 and 10 5 The center frequency of the synthetic aperture sonar is 150kHz, and the bandwidth is set to 40kHz. After simulating the single array echo data using the method of the present invention and the time domain method, the simulation time is as follows: Figure 2 As shown. Figure 2 It can be seen from the figure that when the number of simulation points contained in the scene is sufficiently large, the method of the present invention saves about 3 times the time in the simulation process of a single subarray echo compared to the time domain method. This shows that the method proposed by the present invention is more efficient than the time domain method.
[0097] In order to verify that the simulated echo obtained by the method of the present invention has the same accuracy as the time domain method, an ideal point target with a range coordinate of 35m and an azimuth coordinate of 0m is considered, the platform moving speed v = 5m / s, and the duration of the transmitted signal pulse T = 10ms. The simulated echo signal is as follows: Figure 3 The beam domain imaging algorithm is used to perform imaging processing on the simulated echo signal calculated by the method of the present invention and the simulated echo signal calculated by the high-speed scene time domain method. The results are respectively Figure 4 and Figure 5 As shown in Figure 2, it is verified that the proposed method can well obtain the simulated echo of the high-speed scene. In order to quantitatively evaluate the performance of the method proposed in the present invention, Figure 6 A comparison of the imaging results of the -6dB profile of the echo calculated by the two methods under the beam domain algorithm is given. It can be found from the figure that the two methods can almost obtain the same imaging performance in the imaging results of point targets, and the profile difference is significantly smaller than the theoretical resolution, which shows that the method proposed in the present invention can accurately simulate the echo signal of the synthetic aperture sonar system in high-speed scenes without losing imaging performance. Figure 7 The imaging results of the traditional low-speed scene synthetic aperture sonar echo simulation with the same parameters are given. Figure 7 and Figure 4 , Figure 5 It can be seen that the imaging results of the simulated echoes of the embodiments and the high-speed scene time domain method are defocused due to the motion within the pulse, while the traditional low-speed scene time domain method ignores the motion of the platform within the pulse, and thus cannot reflect the effect of the platform motion within the pulse in the image domain. This shows that the method of the present invention can better simulate the synthetic aperture system echo in high-speed scenes, which indirectly illustrates that the simulation effects of the method of the present invention and the high-speed scene time domain method are essentially different from those of the traditional low-speed scene simulation method.
[0098] Example 2
[0099] The present application also provides a synthetic aperture sonar echo simulation system, which is implemented based on the above method, and the system includes:
[0100] A module for calculating the Doppler scale factor of a target and the frequency of a target after frequency domain scaling, which is used to calculate the Doppler scale factor of a target and the frequency of a target after frequency domain scaling when the target is located within the azimuth beam opening angle of a synthetic aperture;
[0101] A frequency domain echo signal calculation module is used to calculate the frequency domain echo signal of a point target;
[0102] An echo signal calculation module is used to calculate the echo signals of all targets in the imaging scene;
[0103] The module for calculating the time domain simulated echo signal is used to superimpose the frequency domain echo signals of each target and then perform inverse Fourier transform in the range direction to obtain the time domain simulated echo signal.
[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application is described in detail with reference to the embodiments, a person skilled in the art should understand that any modification or equivalent replacement of the technical solution of the present application does not depart from the spirit and scope of the technical solution of the present application and should be included in the scope of the claims of the present application.
Claims
1. A synthetic aperture sonar echo simulation method, comprising: Step S1. When the target is located within the azimuth beam opening angle of the synthetic aperture, the Doppler scale factor of the target and the frequency of the target after frequency domain scale transformation are calculated; Step S2. Calculate the frequency domain echo signal of the point target; Step S3. Calculate the echo signals of all targets in the imaging scene; Step S4. Superimpose the frequency domain echo signals of each target and perform inverse Fourier transform in the range direction to obtain a time domain simulation echo signal; The calculation formula of Doppler scale factor is: Among them, τ n represents the slow time of the nth sampling in azimuth; the mth target is located in the slant range-azimuth plane (r m ,y m ) at; α = v / c is the Doppler factor, that is, the ratio of the platform running speed to the speed of sound in water; It represents the incident angle of the sound ray between the kth subarray and the mth target under the nth azimuth sampling, which is obtained from the geometric relationship between the target and the array element; For The corresponding Doppler scale factor; The frequency calculation formula after frequency domain scaling is: Among them, f r is the distance frequency; is the Doppler scale factor corresponding to the incident angle of the sound ray; f rd is the frequency after distance scale transformation.
2. A synthetic aperture sonar echo simulation method according to claim 1, characterized in that: In step S1, the target is located within the azimuth beam opening angle of the synthetic aperture when the sonar operation position satisfies the following relationship: in, is the relative distance between the platform's operating position and the target's azimuth; r m is the target slant range; the subscripts m and n represent the mth target and the nth azimuth spatial sampling respectively; the superscript k represents the kth subarray; λ is the signal wavelength; and D is the array element aperture.
3. The method for simulating synthetic aperture sonar echo according to claim 1, characterized in that: In step S2, calculating the frequency domain echo signal of the point target includes: Step S2.1 calculates the range spectrum window function of the frequency domain echo signal; Step S2.2 calculates the secondary phase term of the frequency domain echo signal; Step S2.3 calculates the time delay phase term of the frequency domain echo signal; Step S2.4 calculates the echo frequency domain result.
4. The method for simulating synthetic aperture sonar echo according to claim 3, characterized in that: The step S2.1 calculates the range spectrum window function of the frequency domain echo signal, and the calculation formula is as follows: in, represents the range spectrum window function of the frequency domain echo signal corresponding to the Doppler scale factor; f rd is the distance scale transformation frequency; f0 is the carrier frequency; K r is the signal modulation frequency; T is the signal duration; rect(·) is the rectangular window function: Where x represents the rectangular window function parameter.
5. The method for simulating synthetic aperture sonar echo according to claim 3, characterized in that: The step S2.2 calculates the secondary phase term of the frequency domain echo frequency domain signal, and the calculation formula is as follows: in, represents the secondary phase term of the frequency domain echo signal corresponding to the Doppler scale factor; j 2 =-1 is the imaginary unit; K r is the signal modulation frequency; f rd is the distance scale transformation frequency; f0 is the carrier frequency.
6. The method for simulating synthetic aperture sonar echo according to claim 3, characterized in that: The step S2.3 calculates the time delay phase term of the frequency domain echo signal, and the calculation formula is as follows: in, represents the time delay phase term of the frequency domain echo signal corresponding to the Doppler scale factor; 2 =-1 is the imaginary unit; c is the speed of sound in water; f rd is the distance scale transformation frequency; is the equivalent phase center path under slow time scale, and its expression is: Among them, the point target is located in the slant range-azimuth plane (r m ,y m ) at the place; v represents the platform running speed; u k is the distance from the kth receiving array element to the transmitting array element; is the round-trip delay of the sending and receiving process determined according to the geometric relationship; τ n Indicates the slow time of the nth sampling in azimuth; For the case of separate sending and receiving, Replaced with send and receive split sound path The calculation formula is:
7. The method for simulating synthetic aperture sonar echo according to claim 3, characterized in that: The step S2.4 calculates the echo frequency domain result, and the calculation formula is as follows: in, It represents the range frequency domain-azimuth time domain echo received by the kth subarray at the mth target and the nth azimuth spatial sampling; represents the distance spectrum window function; Represents the secondary phase term of the frequency domain echo signal; represents the time delay phase term of the frequency domain echo signal; f rd Represents the distance scale transformation frequency.
8. The method for simulating synthetic aperture sonar echo according to claim 1, characterized in that: In step S4, the frequency domain echo signals of each target are superimposed and then inverse Fourier transform is performed in the range direction to obtain a time domain simulation echo signal, and the calculation formula is: in, It represents the echo signal of the range time domain-azimuth time domain received by the kth subarray at the nth azimuth spatial sampling; Represents the distance scale transformation frequency f t Perform inverse Fourier transform; It represents the range frequency domain-azimuth time domain echo received by the kth subarray for the mth target and the nth azimuth spatial sampling; m = 1, 2, ..., N p is the target ordinal number; f rd is the range scale transformation frequency; the mth target is located in the slant range-azimuth plane (r m ,y m ) at the place; t represents the distance to the fast time; τ n Indicates the slow time of the nth sampling in the azimuth direction.
9. A synthetic aperture sonar echo simulation system, implemented based on any method described in claims 1-8, characterized in that: The system comprises: A module for calculating the Doppler scale factor of a target and the frequency of a target after frequency domain scaling, which is used to calculate the Doppler scale factor of a target and the frequency of a target after frequency domain scaling when the target is located within the azimuth beam opening angle of a synthetic aperture; A frequency domain echo signal calculation module is used to calculate the frequency domain echo signal of a point target; An echo signal calculation module, used for calculating echo signals of all targets in the imaging scene; and The module for calculating the time domain simulated echo signal is used to superimpose the frequency domain echo signals of each target and then perform inverse Fourier transform in the range direction to obtain the time domain simulated echo signal.