A method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR

Abstract

This invention discloses a method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR. The steps are as follows: S1, calculate the key parameters of the interferometric SAR equipment along the ship's wake based on the characteristics of the ship's wake and the electromagnetic wave propagation mechanism; S2, perform normalized SAR interferometry processing on the echo data of the observed scene; S3, detect ship wake pixels based on the normalized interferometry results obtained in step S2; S4, cluster the ship wake pixels based on the information of spatial Euclidean distance and normalized interferometry results; S5, detect the ship's wake; S6, invert the radial velocity field of the ship's wake using interferometric phase information; S7, invert the moving ship parameters using the ship's Kelvin wake; S8, output the ship's wake region, radial velocity field, and corresponding ship speed and heading information. This invention uses the above-mentioned method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR to achieve the acquisition of the ship's wake, the measurement of the radial velocity field of the wake, and the inversion of ship parameters.

Description

Technical Field

[0001] This invention relates to the field of marine remote sensing and surveillance technology, and in particular to a method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR. Background Technology

[0002] Radar offers advantages such as all-weather, 24 / 7 operation and wide-area surveillance, making it crucial for marine remote sensing. Ships, as the primary information input source for human maritime activities, leave wakes in open waters. These wakes are characterized by their long duration, wide spatial distribution, and close correlation with the ship's size, weight, and motion parameters. Radar measurements of ship wake signals are significant for indirectly detecting and estimating the parameters of moving ship targets with low radar cross-sections.

[0003] In existing technologies, SAR ocean images typically show the wakes of moving ships. However, the contrast between the wake image and the ocean background is limited, and the wake is easily affected by wind-driven waves around the wake, making ship wake measurements unreliable. G. Zilman, A. Zapolski, and M. Marom, in their article "The speed and beam of a ship from its wake's SAR images" published in Volume 42, Issue 10 of the journal *IEEE Transactions on Geoscience and Remote Sensing*, disclosed a method for obtaining ship speed and beam from wake SAR images. This method is based on the linear characteristics of wakes in SAR images, using the Fast Discrete Radon Transform to extract the Kelvin and turbulent wakes of moving ships in the SAR image domain. Then, model analysis is performed on the Kelvin and turbulent wakes respectively to deduce the corresponding ship speed and beam information. However, as sea state increases, the surface wave motion becomes more intense, and the wake wave continuously attenuates, weakening its intensity in the SAR image. Furthermore, the increased resolution of SAR images and changes in radar observation angles cause the wakes to no longer exhibit linear characteristics, but rather show features similar to area targets in optical images. This renders wake detection methods that utilize linear features ineffective, and further leads to a significant discrepancy between the ship parameter inversion results and the actual situation. Summary of the Invention

[0004] The purpose of this invention is to provide a method for acquiring the wake region and measuring the wake velocity field of moving ships using interferometric SAR, overcoming the shortcomings of the prior art, and combining multi-dimensional information of the wake to improve the probability of acquiring the wake of moving ships under complex sea conditions.

[0005] To achieve the above objectives, this invention provides a method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR, the steps of which are as follows:

[0006] S1. Based on the characteristics of ship wakes and the electromagnetic wave propagation mechanism, calculate the key parameters of the along-track interferometric SAR equipment;

[0007] S2. Perform normalized SAR interferometry processing on the echo data of the observed scene;

[0008] S3. Detect ship wake pixels based on the normalized interferometric results obtained in step S2;

[0009] S4. Cluster the ship wake pixels based on information from spatial Euclidean distance and normalized interferometry results;

[0010] S5. Ship stern track detected;

[0011] S6. Invert the radial velocity field of the ship's wake using interferometric phase information;

[0012] S7. Invert the parameters of a moving ship using the ship's Kelvin wake;

[0013] S8. Output the ship wake region, the ship wake radial velocity field, and the ship speed and heading information corresponding to the ship wake, respectively.

[0014] Preferably, the interferometric SAR device in step S1 adopts a full-aperture transmit-sub-aperture independent receive mode, and the full-aperture transmit-sub-aperture independent receive mode uses the RD imaging method to perform SAR imaging on the echo data received by each subarray.

[0015] The key parameters include the product of the radar's average transmit power and the antenna's transmit and receive aperture X, the transmit antenna area S, and the antenna length along the flight direction D. a Antenna vertical heading length D e The antenna elements, the spacing d between adjacent receiving subarrays, and the signal bandwidth B are calculated using the following methods:

[0016] 1) The product of radar average transmit power and antenna transmit / receive aperture:

[0017]

[0018] Where X represents the product of the radar's average transmit power and the antenna's transmit and receive aperture, denoted as X = P av G t G r P av G represents the average transmit power of the interferometric SAR device along the flight path. t G represents the transmit antenna gain of the along-track interferometric SAR device. rThe gain of the receiving antenna of the along-track interferometric SAR device is represented by β0, the power ratio of the wake to the noise is represented by β0, k is the Boltzmann constant, and T0 is the system noise temperature of the along-track interferometric SAR device. B The noise bandwidth correction factor is represented by F, the receiver noise figure of the along-track interferometric SAR device is represented by L, the system loss of the along-track interferometric SAR device is represented by R, and the slant range between the along-track interferometric SAR device and the wake of the ship to be measured is represented by T. a λ represents the coherent accumulation time of the along-track interferometric SAR device, λ represents the wavelength of the electromagnetic wave emitted by the along-track interferometric SAR device, and σ represents the radar cross-section of the ship's wake.

[0019] 2) Transmitting antenna area:

[0020]

[0021] Where N represents the number of subarrays into which the antenna is divided, a1 represents the antenna efficiency, a2 represents the pulse duty cycle, and P0 represents the radiated power of a single antenna.

[0022] 3) Antenna length along the flight direction:

[0023]

[0024] Where W represents the width of the observation scene, which is greater than the maximum width of the ship's wake area;

[0025] 4) Antenna vertical heading length:

[0026] D e ≤D a

[0027] 5) The antenna elements are rectangular planar arrays arranged at half wavelengths, and satisfy the following constraints:

[0028]

[0029] Where b represents the total number of antenna elements, b a b represents the number of antenna elements along the flight path. b This indicates the number of antenna elements in the direction perpendicular to the flight path; <·> indicates the rounding operation.

[0030] 6) Spacing between adjacent receiver subarrays:

[0031]

[0032] Among them, V a L represents the platform's speed along the trajectory. K The wavelength of the Kelvin wake wave of a ship is denoted as . g represents the acceleration due to gravity, which is 9.8 m / s². 2 Us Indicates the ship's speed;

[0033] 7) The signal bandwidth satisfies the following constraints:

[0034]

[0035] Where c represents the speed of light.

[0036] Preferably, the normalized SAR interferometry processing in step S2 involves recording a set of SAR complex image data from adjacent subarrays, denoted as z1(n) and z2(n), and the calculation method is as follows:

[0037]

[0038] Where n represents the index of a pixel in the SAR image, Z(n) represents the normalized interferometric result of the nth pixel, K represents the number of multiviews, taking the K pixels in the SAR image that are closest to the nth pixel, * represents the conjugate operation, and E[·] represents the mathematical expectation operation.

[0039] The result of the normalized SAR interferometry is the interferometric amplitude and phase of the observed scene, denoted by ξ(n) and The normalized interference amplitude and interference phase of the n pixels are represented respectively, as follows:

[0040]

[0041]

[0042] Preferably, the normalized interference result is based on the interference amplitude and interference phase information of pixels, and the specific detection steps in step S3 are as follows:

[0043] S31. Construct the ship's wake pixel detection quantity according to the following formula:

[0044]

[0045] Where T(n) represents the detection quantity of the nth pixel, and ξ(n) and ξ represents the normalized interference amplitude and interference phase of the nth pixel, respectively. s and These represent the mean and standard deviation of the interference amplitude in the sea clutter background, respectively. and These represent the mean and standard deviation of the interference phase in the sea clutter background, respectively.

[0046] S32. Pixels with T(n)≥η are taken as ship wake pixels, where η represents the wake pixel detection threshold.

[0047] Preferably, the specific steps of clustering in step S4 are as follows:

[0048] S41, Let the set G be the group of pixels representing the ship's stern. t The spatial Euclidean distance between pixels m and n is denoted as P. m , n The difference in interference amplitude is denoted as A. m,n =|ξ(m)-ξ(n)|, the interference phase difference is denoted as Construct feature vectors [P] for pixels m and n m,n A m,n B m,n ];

[0049] S42, in set G t In the process, iterate through the data and determine whether the feature vectors of the m-th pixel and the n-th pixel satisfy the following formula:

[0050]

[0051] Where m1, m2, and m3 represent three adjustment coefficients, and m1 > 0, m2 > 0, m3 > 0, δ A δ represents the threshold for the difference in interference amplitude. A ≥0, δ P This represents the spatial distance threshold for clustering, which is... δ B This represents the threshold for interference phase difference, which is... v0 represents the radial velocity change scale of the trail pixel;

[0052] If the condition is met, the m-th pixel and the n-th pixel are grouped into one class; if the condition is not met, they are not grouped into one class. Any two classes with common pixels are merged into the same class.

[0053] S43, For set G t After clustering the pixels in step S42, H pixel classes are obtained.

[0054] Preferably, the ship wake detection step in step S5 is as follows:

[0055] S51. Perform area checks on H pixel classes, calculate the minimum bounding area of ​​each pixel class, and compare it with the area threshold. Keep the pixel classes that are greater than the area threshold and remove the pixel classes that are less than the area threshold. After the H pixel classes have been checked for area, they are recorded as H1 pixel classes.

[0056] S52. Extract the minimum bounding shape of each of the H1 pixel classes. Perform a graphic inspection on the H1 pixel classes. Pixel classes whose minimum bounding shape is close to an acute triangle are retained, and pixel classes that are not close are removed. M pixel classes are obtained as M ship wakes.

[0057] Preferably, the radial velocity field of the ship's wake in step S6 is calculated as follows:

[0058]

[0059] Among them, v w (n) represents the radial velocity of pixel n in the trail region.

[0060] Preferably, the specific steps of the inversion in step S7 are as follows:

[0061] S71. For each ship wake, extract the acute-angled edges from its image as its respective Kelvin wake, and use FFT to obtain the Kelvin wake spectral distribution. The maximum spectral peak corresponds to the wave number k of the Kelvin wake wave. d Estimate the ship's speed corresponding to its wake. The calculation method is as follows:

[0062]

[0063] S72. The direction of the angle bisector of the two Kelvin trail angles of each ship's wake is recorded as its corresponding ship's course, wherein the two Kelvin trail angles in the wake point to its corresponding ship's sailing direction.

[0064] Therefore, the present invention employs the aforementioned method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR, which is applicable to microwave measurement of the wake of a moving ship, the velocity field of the wake region, and the inversion of parameters of the corresponding ship target. Its technical advantages are as follows:

[0065] 1) By combining the distribution characteristics of the wake wave of a moving ship with the electromagnetic wave scattering mechanism, this invention designs the parameters of the interferometric SAR equipment, which can obtain accurate interferometric measurement information and velocity field information of the wake of a moving ship.

[0066] 2) This invention combines the interference amplitude and interference phase information of the wake of a moving ship to construct an enhanced detection quantity for the wake of a moving ship, improves the contrast between the wake of a moving ship and the sea clutter background, and improves the acquisition probability of the wake of a moving ship and the detection performance of pixels under complex sea conditions.

[0067] 3) By performing image analysis on the wake of a moving ship, this invention can deduce motion parameters such as the radial velocity field of the wake region of the corresponding ship.

[0068] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0069] Figure 1This is a flowchart of a method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR according to the present invention;

[0070] Figure 2 This invention relates to a method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR, which yields a scene interferometric amplitude map.

[0071] Figure 3 This invention relates to a method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR, which yields a scene interferometric phase map.

[0072] Figure 4 This invention relates to a method for obtaining the wake region of a moving ship using interferometric SAR and measuring its wake velocity field, which extracts the wake region.

[0073] Figure 5 This invention relates to a method for obtaining the wake region and measuring the wake velocity field of a moving ship using interferometric SAR, which extracts the Kelvin wake spectrum distribution in the wake region.

[0074] Figure 6 The radial velocity inversion result of the wake region obtained by the method of obtaining the wake region and measuring the wake velocity field of a moving ship by interferometric SAR according to the present invention. Detailed Implementation

[0075] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0076] like Figure 1 The flowchart shown illustrates a method for combining interferometric SAR for acquiring the wake region and measuring the wake velocity field of a moving ship. The specific implementation steps are as follows:

[0077] S1. Based on the wake height distribution, velocity field distribution, and electromagnetic wave propagation mechanism of a moving ship, calculate the antenna aperture, receiving subarray spacing, and transmitted signal bandwidth of the interferometric SAR equipment along the flight path. The interferometric SAR equipment adopts a full-aperture transmit sub-aperture independent receive mode. For the echo data received by each subarray, SAR imaging is performed using the RD imaging method.

[0078] 1) The product X of the radar's average transmit power and the antenna's transmit / receive aperture is determined by the following formula:

[0079]

[0080] Where X represents the product of the radar's average transmit power and the antenna's transmit and receive aperture, denoted as X = P av G t G r P av G represents the average transmit power of the interferometric SAR device along the flight path. tG represents the transmit antenna gain of the along-track interferometric SAR device. r The gain of the receiving antenna of the along-track interferometric SAR device is represented by β0, the power ratio of the wake to the noise is represented by β0, k is the Boltzmann constant, and T0 is the system noise temperature of the along-track interferometric SAR device. B The noise bandwidth correction factor is represented by F, the receiver noise figure of the along-track interferometric SAR device is represented by L, the system loss of the along-track interferometric SAR device is represented by R, and the slant range between the along-track interferometric SAR device and the wake of the ship to be measured is represented by T. a λ represents the coherent accumulation time of the along-track interferometric SAR device, λ represents the wavelength of the electromagnetic wave emitted by the along-track interferometric SAR device, and σ represents the radar cross-section of the ship's wake.

[0081] 2) Based on the product X of the radar's average transmit power and the antenna's transmit and receive aperture, calculate the transmit antenna area S of the interferometric SAR equipment along the flight path using the following formula:

[0082]

[0083] Where N represents the number of subarrays into which the antenna is divided, a1 represents the antenna efficiency, a2 represents the pulse duty cycle, and P0 represents the radiated power of a single antenna.

[0084] 3) Antenna length D along the flight direction of the track-based interferometric SAR device a Satisfy the following formula:

[0085]

[0086] Where W represents the width of the observation scene, which is greater than the maximum width of the ship's wake area.

[0087] 4) Vertical heading length D of the antenna of the interferometric SAR device along the flight path e Satisfy the following formula:

[0088] D e ≤D a

[0089] 5) The antenna elements of the track-based interferometric SAR equipment are rectangular planar arrays arranged at half wavelengths, and satisfy the following constraints:

[0090]

[0091] Where b represents the total number of antenna elements, b a b represents the number of antenna elements along the flight path. b This indicates the number of antenna elements in the vertical track direction, and <·> indicates the rounding operation.

[0092] 6) The spacing d between adjacent receiver subarrays of the interferometric SAR equipment along the flight path needs to satisfy the following formula:

[0093]

[0094] Among them, V a L represents the platform's speed along the trajectory. K The wavelength of the Kelvin wake wave of a ship is denoted as . g represents the acceleration due to gravity, which is 9.8 m / s². 2 U s Indicates the ship's speed.

[0095] 7) The signal bandwidth B constraint of the interferometric SAR equipment along the flight path is as follows:

[0096]

[0097] Where c represents the speed of light.

[0098] S2. Perform normalized SAR interferometry on the echo data of the observed scene, i.e., use interferometric SAR equipment to obtain the interference amplitude and phase of the observed scene. Let z1(n) and z2(n) be the SAR complex image domain data of a set of adjacent subarrays. Perform normalized interferometry on the SAR images of the two subarrays according to the following formula:

[0099]

[0100] Where n represents the index of a pixel in the SAR image, Z(n) represents the normalized interferometric result of the nth pixel, K represents the multi-look number, which is the K pixels in the SAR image that are closest to the nth pixel, * represents the conjugate operation, and E[·] represents the mathematical expectation operation.

[0101] Using ξ(n) and The normalized interference amplitude and interference phase of the nth pixel are represented respectively, as follows:

[0102]

[0103]

[0104] S3. Using the normalized interference results obtained in step S2, i.e., based on the interference amplitude and phase information of the pixels, the ship's wake pixels are detected. The specific steps are as follows:

[0105] S31, Detection count of ship wake pixels:

[0106]

[0107] Where T(n) represents the detection quantity of the nth pixel, ξ s and These represent the mean and standard deviation of the interference amplitude in the sea clutter background, respectively. and These represent the mean and standard deviation of the interference phase in the sea clutter background, respectively.

[0108] S32. Pixels with T(n)≥η are taken as ship wake pixels, where η represents the wake pixel detection threshold.

[0109] S4. Cluster the moving ship wake pixels detected in step S3 based on the consistency of spatial Euclidean distance, interference amplitude, and interference phase. The specific steps are as follows:

[0110] S41. Let the group of detected moving ship wake pixels be set G. t The spatial Euclidean distance between pixels m and n is denoted as P. m,n The difference in interference amplitude is denoted as A. m,n =|ξ(m)-ξ(n)|, the interference phase difference is denoted as Construct feature vectors [P] for pixels m and n m,n A m,n B m,n ].

[0111] S42, in set G t In the process, iterate through the data and determine whether the feature vectors of the m-th pixel and the n-th pixel satisfy the following formula:

[0112]

[0113] Where m1, m2, and m3 represent three adjustment coefficients, and m1 > 0, m2 > 0, m3 > 0, δ A δ represents the threshold for the difference in interference amplitude. A ≥0, δ P This represents the spatial distance threshold for clustering, which is... δ B This represents the threshold for interference phase difference, which is... v0 represents the radial velocity change scale of the trail pixel.

[0114] If the condition is met, the m-th pixel and the n-th pixel are grouped into one class; otherwise, they are not grouped into one class. Any two classes with common pixels are merged into one class.

[0115] S43, For set G t The pixels are clustered in step S42 to obtain H pixel classes.

[0116] S5. Perform area and pattern checks on the H pixel classes from step S4 to obtain M pixel classes, which are used as the M detected ship wakes. The specific steps are as follows:

[0117] S51. Perform area checks on H pixel classes, calculate the minimum bounding area of ​​each pixel class, and compare it with the area threshold. Pixel classes with an area greater than the area threshold are retained, and pixel classes with an area less than the area threshold are removed. The H pixel classes are then reduced to H1 pixel classes after the area check.

[0118] S52. Extract the minimum bounding shape of each of the H1 pixel classes. Perform a shape inspection on the H1 pixel classes. Keep the minimum bounding shape that is close to an acute triangle and remove the one that is not. Finally, obtain M pixel classes as M ship wakes.

[0119] S6. The radial velocity field of the wake is inverted using the interferometric phase information, and the calculation method is as follows:

[0120] Take one ship wake from among M ship wakes, and invert its radial velocity according to the interference phase of the pixels in the wake region using the following formula:

[0121]

[0122] Among them, v w (n) represents the radial velocity of pixel n in the trail region.

[0123] S7. Invert the parameters of the moving ship using the Kelvin wake of the ship's wake. The specific steps are as follows:

[0124] S71. For each ship wake, extract the acute-angled edges from its image as its respective Kelvin wake, and use FFT to obtain the Kelvin wake spectral distribution. The maximum spectral peak corresponds to the wave number k of the Kelvin wake wave. d Estimate the ship's speed corresponding to its wake using the following formula.

[0125]

[0126] S72. The direction of the angle bisector of the two Kelvin trail angles of each ship's wake is recorded as its corresponding ship's course, wherein the two Kelvin trail angles in the wake point to its corresponding ship's sailing direction.

[0127] S8. Output the M wake regions, their radial velocity fields, and the corresponding ship speed and heading information respectively.

[0128] Experimental test:

[0129] The experimental environment for this invention was: MATLAB R2010a, Intel(R) Core(TM) 2 Duo CPU 3.4GHz, Windows XP Professional Edition.

[0130] The experiment of this invention is based on a dual-channel airborne interferometric SAR system, employing a full-aperture transmit-sub-aperture receive mode. The interferometric SAR equipment is placed on an aircraft at a platform speed of 50 m / s and an altitude of 5000 m. The interferometric SAR operates at a frequency of 3 GHz, with an antenna transmit / receive aperture of 2.5 × 0.1 m (along the flight path × perpendicular to the flight path). There are two receiver subarrays, evenly spaced with a centroid spacing of 1.25 m. The transmitted signal bandwidth is 67 MHz. A linear frequency modulated signal is used, with a pulse repetition rate of 500 Hz, a pulse duty cycle of 15%, and a coherent accumulation time of 1 s.

[0131] In the experiment, the simulated ship target was 160m long, 20m wide, with a draft of 5m and a speed of 20m / s. Based on the designed equipment parameters, the echoes from the sea surface and wake region were simulated, SAR-imagined, and normalized interferometric processed.

[0132] Figure 2 The scene interference amplitude obtained by this invention. Figure 3 This represents the interference amplitude obtained by the present invention. It can be seen that the interference amplitude and phase in the wake region of the moving ship are different from those in the surrounding sea area, and the wake characteristics of the ship are clearly visible.

[0133] Figure 4 This is the tail region extracted in this invention. Figure 5 This shows the Kelvin wake spectral distribution extracted from the wake region in this invention. The wavenumber of the Kelvin wave can be obtained from the Kelvin spectral peak value using the formula... The estimated speed of the ship is 19.7 m / s, which is very close to the actual speed of the simulated ship target, 20 m / s.

[0134] Figure 6 The radial velocity inversion result of the wake region obtained by this invention shows that the radial velocity information corresponding to each pixel in the wake region can be read from the grayscale values ​​on the right side of the image, thus realizing the inversion of the corresponding ship's motion parameters. This experiment verifies the effectiveness of this invention.

[0135] Therefore, the present invention employs the above-mentioned method for acquiring the wake region and measuring the wake velocity field of moving ships using interferometric SAR, which can obtain the interference amplitude and interference phase information of the wake of moving ships, expand the measurement dimension of the wake of moving ships, alleviate the influence of other wave systems on the detection of wake waves of moving ships, obtain more accurate measurement results of the wake region and its velocity field of moving ships, and further improve the reliability of the indirect inversion method of ship parameters based on the wake of ships.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR, characterized in that: The steps are as follows: S1. Based on the characteristics of ship wakes and the electromagnetic wave propagation mechanism, calculate the key parameters of the along-track interferometric SAR equipment; S2. Perform normalized SAR interferometry processing on the echo data of the observed scene; S3. Detect ship wake pixels based on the normalized interferometric results obtained in step S2; S4. Cluster the ship wake pixels based on information from spatial Euclidean distance and normalized interferometry results; S5. Ship stern track detected; S6. Invert the radial velocity field of the ship's wake using interferometric phase information; S7. Invert the parameters of a moving ship using the ship's Kelvin wake; S8. Output the ship wake region, the ship wake radial velocity field, and the ship speed and heading information corresponding to the ship wake, respectively. The interferometric SAR equipment in step S1 adopts the full aperture transmit sub-aperture independent receive mode. The full aperture transmit sub-aperture independent receive mode uses the RD imaging method to perform SAR imaging on the echo data received by each subarray. The key parameters include the product of radar average transmit power and antenna transmit / receive aperture X, transmit antenna area S, antenna length along the flight direction Da, antenna length perpendicular to the flight direction De, antenna elements, spacing d between adjacent receiver subarrays, and signal bandwidth B. The calculation methods used are as follows: 1) The product of radar average transmit power and antenna transmit / receive aperture: Where X represents the product of the radar's average transmit power and the antenna's transmit and receive aperture, X = PavGtGr, Pav represents the average transmit power of the along-track interferometric SAR device, Gt represents the transmit antenna gain of the along-track interferometric SAR device, Gr represents the receive antenna gain of the along-track interferometric SAR device, β0 represents the wake-to-noise power ratio, k is the Boltzmann constant, T0 is the system noise temperature of the along-track interferometric SAR device, CB represents the noise bandwidth correction factor, F is the receiver noise figure of the along-track interferometric SAR device, L represents the system loss of the along-track interferometric SAR device, R represents the slant range between the along-track interferometric SAR device and the wake of the ship to be measured, Ta represents the coherent accumulation time of the along-track interferometric SAR device, λ represents the wavelength of the electromagnetic wave emitted by the along-track interferometric SAR device, and σ represents the radar cross-section of the ship's wake. 2) Transmitting antenna area: Where N represents the number of subarrays into which the antenna is divided, a1 represents the antenna efficiency, a2 represents the pulse duty cycle, and P0 represents the radiated power of a single antenna. 3) Antenna length along the flight direction: Where W represents the width of the observation scene, which is greater than the maximum width of the ship's wake area; 4) Antenna vertical heading length: De ≤Da 5) The antenna elements are rectangular planar arrays arranged at half wavelengths, and satisfy the following constraints: Where b represents the total number of antenna elements, ba represents the number of antenna elements along the track direction, bb represents the number of antenna elements perpendicular to the track direction, and < ·> represents the rounding operation; 6) Spacing between adjacent receiver subarrays: Where Va represents the platform's speed along its trajectory, and LK represents the wavelength of the ship's Kelvin wake. g represents the acceleration due to gravity, which is 9.8 m / s², and Us represents the ship's speed. 7) The signal bandwidth satisfies the following constraints: Where c represents the speed of light.

2. The method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR according to claim 1, characterized in that: The normalized SAR interferometry processing in step S2 involves recording a set of SAR complex image data from adjacent subarrays, denoted as z1(n) and z2(n), and its calculation method is as follows: Where n represents the index of a pixel in the SAR image, Z(n) represents the normalized interferometric result of the nth pixel, K represents the number of multiviews, taking the K pixels in the SAR image that are closest to the nth pixel, * represents the conjugate operation, and E[·] represents the mathematical expectation operation; The result of the normalized SAR interferometry is the interferometric amplitude and phase of the observed scene, denoted by ξ(n) and The normalized interference amplitude and interference phase of the n pixels are represented respectively, as follows: 。 3. The method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR according to claim 2, characterized in that: The normalized interference result is based on the interference amplitude and interference phase information of pixels. The specific detection steps in step S3 are as follows: S31. Construct the ship's wake pixel detection quantity according to the following formula: Where T(n) represents the detection quantity of the nth pixel, and ξ(n) and Let ξn represent the normalized interference amplitude and interference phase of the nth pixel, and let ξs and hξs represent the mean and standard deviation of the interference amplitude of the sea clutter background, respectively. and These represent the mean and standard deviation of the interference phase in the sea clutter background, respectively. S32. Pixels with T(n) ≥ η are taken as ship wake pixels, where η represents the wake pixel detection threshold.

4. The method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR according to claim 3, characterized in that: The specific steps of clustering in step S4 are as follows: S41. Let the set of ship wake pixels be Gt, the spatial Euclidean distance between pixels m and n be Pm,n, the difference in interference amplitude be Am,n = |ξ(m)-ξ(n)|, and the difference in interference phase be denoted as... Construct the feature vectors [Pm,n,Am,n,Bm,n] for pixels m and n; S42. In set Gt, iterate through the set and determine whether the feature vectors of the m-th pixel and the n-th pixel satisfy the following formula: Where m1, m2, and m3 represent three adjustment coefficients, with m1 > 0, m2 > 0, and m3 > 0, and δA represents the threshold for the difference in interference amplitude. δA ≥ 0, δP represents the spatial distance threshold for clustering, which is... δB represents the interference phase difference threshold, which is... v0 represents the radial velocity change scale of the trail pixel. If it is satisfied, the m-th pixel and the n-th pixel are clustered into one class. If it is not satisfied, they are not clustered into one class. Any two classes with common pixels are merged into the same class. S43. After performing the clustering of pixels in set Gt in step S42, H pixel classes are obtained.

5. The method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR according to claim 4, characterized in that: The detection steps for the ship's wake in step S5 are as follows: S51. Perform area checks on H pixel classes, calculate the minimum bounding area of ​​each pixel class, and compare it with the area threshold. Keep the pixel classes that are greater than the area threshold and remove the pixel classes that are less than the area threshold. After the H pixel classes have been checked for area, they are recorded as H1 pixel classes. S52. Extract the minimum bounding shape of each of the H1 pixel classes. Perform a graphic inspection on the H1 pixel classes. Pixel classes whose minimum bounding shape is close to an acute triangle are retained, and pixel classes that are not close are removed. M pixel classes are obtained as M ship wakes.

6. The method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR according to claim 5, characterized in that: The radial velocity field of the ship's wake in step S6 is calculated as follows: Where vw(n) represents the radial velocity of pixel n in the trail region.

7. The method for acquiring the wake region and measuring the wake velocity field of a moving ship using interferometric SAR as described in claim 6. Its features are: The specific steps of the inversion in step S7 are as follows: S71. For each ship wake, extract the acute-angled edges from its image as its respective Kelvin wake. Use FFT to obtain the Kelvin wake spectral distribution. The maximum spectral peak corresponds to the wave number kd of the Kelvin wake wave. Estimate the ship speed corresponding to the ship wake. The calculation method is as follows: S72. The direction of the angle bisector of the two Kelvin trail angles of each ship's wake is recorded as its corresponding ship's course, wherein the two Kelvin trail angles in the wake point to its corresponding ship's sailing direction.

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