Ocean vector current retrieval method based on squint ATI-SAR multi-aspect sub-aperture focusing

Abstract

The present application relates to the technical field of marine remote sensing observation, in particular to a kind of oblique ATI-SAR multi-viewing direction sub-aperture focusing marine vector flow inversion method.The present application includes the following steps: the observation of oblique ATI-SAR load, the focusing of multi-viewing direction sub-aperture, the inversion of multi-viewing direction HLOS flow rate, the solution of vector flow overdetermined equation, the test of vector flow internal and external consistency.The present application uses non-normal side-looking observation, uses physical oblique to enhance the observability along the track component, and keeps single-beam low cost and system simple;The present application can obtain much larger along-track component than "virtual oblique" because the contribution of azimuth component is proportional to the sine of oblique angle, which improves the solvability of equation and reduces the instability of inversion;With small system burden, intuitive and reliable observation information is obtained, equipment investment is saved, and scalable vector flow on-orbit observation is realized.The present application is a "three-step walk" closed-loop process, which breaks through the bottleneck of traditional technology in engineering usability and result robustness.

Description

Technical Field

[0001] This invention relates to the field of marine remote sensing observation technology, specifically to a method for inverting marine vector currents using oblique-view ATI-SAR multi-view sub-aperture focusing. Background Technology

[0002] High-quality sea surface vector current observations, which simultaneously acquire both direction and magnitude information, are of great significance for climate research, understanding of ocean processes, and applications in shipping, fisheries, and pollution diffusion monitoring. Currently, there are various methods for acquiring sea surface currents: direct field measurements, such as those using moorings, buoys, and ADCP, are intuitive and reliable, but costly and have limited spatial coverage; shore-based high-frequency radar (HFR) facilitates continuous near-shore monitoring, but is limited by observation range and geometric and environmental conditions; satellite remote sensing offers long-term data, wide coverage, and lower cost; altimeters provide geostrophic current information but lack spatial detail; and synthetic aperture radar (SAR) offers all-weather, high-resolution performance. Among SAR current measurement techniques, Doppler spectral anomaly (DCA) and along-track interferometry (ATI-SAR) are representative, but both DCA and traditional single-beam ATI are limited by front-side observation and centrally symmetrical imaging, only acquiring radial velocity along the line of sight and being insensitive to along-track components, making it difficult to recover complete vector currents. Scholars have proposed various modification paths, such as Chinese Patent Publication No. CN117590345A, which discloses a method, system and medium for removing phase of time-varying cross-track error in ATI-SAR. However, the implementation cost and system complexity are high, error coupling amplification leads to increased uncertainty, and the engineering cost is high. Multi-aperture along-track interferometry MA-ATI has limited "virtual oblique angle", weak contribution of azimuth component, sensitivity to error, and insufficient marine verification, making it difficult to implement on a large scale in engineering. Summary of the Invention

[0003] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a method for ocean vector current inversion by focusing multiple angle sub-apertures in oblique-view ATI-SAR.

[0004] The technical solution adopted in this invention is as follows:

[0005] A method for ocean vector current inversion using oblique-looking ATI-SAR multi-view sub-aperture focusing includes the following steps:

[0006] S1. Observation of the oblique-looking ATI-SAR payload: Based on the oblique-looking ATI-SAR payload device carried by the satellite, electromagnetic waves are emitted towards the same ocean surface along the flight direction, and the original echo signals of the two channels after being reflected by the ocean surface are observed.

[0007] S2. Multi-view sub-aperture focusing: Based on the multi-center Doppler frequency and sub-band width, the original echo signal is divided into multiple view sub-apertures and focused independently, outputting two-channel SLC image pairs with different view directions;

[0008] S3. Inversion of HLOS velocities in multiple directions: Along-track interferometry is performed on two-channel SLC image pairs with different directions to obtain the interferometric phase, and the HLOS velocities in multiple directions are obtained by inversion of the interferometric phase.

[0009] S4. Solving the overdetermined equations of the vector current: Based on the observation geometry, establish the overdetermined equations between the multi-view HLOS velocity and the vector current to be determined, and use the least squares method to solve for the ocean vector current composed of the along-track and cross-track components.

[0010] S5. Verification of internal and external consistency of vector currents: Perform internal and external consistency verification on the obtained ocean vector currents and output the evaluation inversion results.

[0011] This technical solution uses a satellite-borne oblique-looking ATI-SAR payload to transmit electromagnetic waves and receive two channels of raw echo signals reflected from the ocean surface, thereby acquiring initial information about the ocean surface. Then, based on the multi-center Doppler frequency and sub-band width, the raw echo signals are divided into multiple line-of-sight sub-apertures and focused separately to obtain two-channel SLC image pairs from different line-of-sight directions, enriching ocean information from multiple angles. Next, along-track interferometry is performed on the SLC image pairs from different line-of-sight directions to obtain the interferometric phase, which is then inverted to obtain multi-line-of-sight HLOS current velocities, converting image information into current velocity information. Then, overdetermined equations are established based on observation geometry, and the least squares method is used to solve for the ocean vector current, realizing the derivation from partial velocity information to the complete vector current. Finally, the obtained ocean vector current is subjected to internal and external consistency checks to evaluate the accuracy of the inversion results, ensuring that reliable and stable ocean vector current information is ultimately obtained. This technical solution employs non-frontal side-looking observation to enhance the observability of the track-direction components, maintaining the low cost and simplicity of a single beam and system, thus obtaining intuitive and reliable observation information with a small system burden. It reduces errors by dividing the original echo sub-bands, constructs a multi-line-of-sight overdetermined equation system and uses the least squares method to reduce random errors, and proposes a consistency check to evaluate the inversion results, thereby improving reliability. It systematically resolves the bottlenecks of traditional technical methods, achieving breakthroughs in engineering usability and result robustness, and filling the gap in reliable observation and inversion technology for single-beam ATI-SAR vector flow.

[0012] In addition, the ocean vector current inversion method based on oblique-looking ATI-SAR multi-view sub-aperture focusing proposed according to the present invention can also have the following additional technical features:

[0013] According to one embodiment of the present invention, in the observation of the slant-look ATI-SAR payload in step S1, the physical slant angle of the slant-look ATI-SAR payload device is set to be greater than 3°, which is used to enhance the observability of the azimuth velocity component.

[0014] In this technical solution, when the physical angle of inclination is greater than 3°, the propagation direction of the electromagnetic wave forms a certain angle with the normal direction of the ocean surface; the slight azimuth movement of the ocean surface will cause the reflected electromagnetic wave to produce a Doppler frequency shift, and the frequency shift is closely related to the azimuth velocity component; the larger angle of inclination amplifies the Doppler effect, making the frequency shift caused by the azimuth velocity component more significant, thus making it easier to detect and distinguish in the received echo signal.

[0015] According to an embodiment of the present invention, the multi-view aperture focusing in step S2 includes the following specific steps:

[0016] S21. Assume the Doppler center frequency of the original echo signal is... Calculate the first [value] under a given viewing angle. The angle between the aperture view and the frontal / side view The formula is as follows:

[0017] (1)

[0018] In the formula: The physical angle of view of the beam. For the first The angle of view of each aperture relative to the beam center line of view;

[0019] S22. Based on the Doppler subband method, first perform FFT on the original echo signal along the azimuth direction; at the subband center frequency... Applying a bandpass window with a bandwidth equal to the subband width at a given point yields the corresponding subband spectrum; the subband center frequency... The formula is as follows:

[0020] (2)

[0021] In the formula: For platform speed, For the operating wavelength, For the first The angle between the line of sight and the side-view direction; the Doppler center frequency of the central line of sight. ;

[0022] Then, an azimuth IFFT is performed on each sub-band to return to the time domain, obtaining the original sub-data for each line of sight;

[0023] S23. Based on the Chirp Scaling algorithm, the original sub-data of each viewing direction is imaged and focused to output two-channel SLC image pairs of different viewing directions.

[0024] This technical solution enables multi-view aperture focusing by analyzing the Doppler characteristics of the original echo signal. Specifically, based on the platform speed, operating wavelength, and the opening angle of the sub-aperture view relative to the beam center view, a specific formula is used to calculate the Doppler shift of different sub-apertures at a given view angle. Because the echo signals from different view directions will produce different Doppler frequency shifts due to platform motion and observation angle differences, this calculation can accurately quantify this difference. Using the Doppler sub-band method, the original echo signal is subjected to azimuth FFT to transform it into the frequency domain for frequency component analysis. Then, a bandpass window is applied at the sub-band center frequency to obtain the sub-band spectrum. The sub-band center frequency is determined by relevant formulas, thereby separating the frequency ranges corresponding to different view directions. After that, azimuth IFFT is performed back to the time domain to obtain the original sub-data for each view direction, realizing the initial division of the signal in the view direction. The Chirp Scaling algorithm is used to image and focus the original sub-data for each view direction, effectively handling the phase error problem in the signal propagation process, focusing the dispersed energy, and finally outputting two-channel SLC image pairs for different view directions.

[0025] According to an embodiment of the present invention, the two-channel SLC image pair with different viewing directions in step S23 includes:

[0026] The center line of sight SLC1, line of sight 1 SLC1, line of sight 2 SLC1, up to line of sight n SLC1 in channel 1;

[0027] The center line of sight SLC2, line of sight 1 SLC2, line of sight 2 SLC2, up to line of sight n SLC2 in channel 2;

[0028] Wherein: center view SLC1 and center view SLC2 are one SLC image pair; view 1 SLC1 and view 1 SLC2 are one SLC image pair; view 2 SLC1 and view 2 SLC2 are one SLC image pair, and so on, until view n SLC1 and view n SLC2 are one SLC image pair.

[0029] In this technical solution, Channel 1 and Channel 2 receive echo signals from different receiving channels respectively. For each line of sight, such as the central line of sight, line of sight 1, line of sight 2, up to line of sight n, a corresponding SLC image will be formed in Channel 1 and Channel 2. Because different regions of the ocean surface have different scattering characteristics under different line of sight and channel combinations, this multi-line of sight and multi-channel observation method can capture information about the ocean surface from different angles and polarization characteristics, enriching the data dimensions.

[0030] According to an embodiment of the present invention, the inversion of multi-view HLOS flow velocity in step S3 includes the following specific steps:

[0031] S31. For two-channel SLC images with different viewing directions, the interference is processed along the track. The interference is obtained by sub-pixel level registration, forming interference phase, channel phase deviation correction and multi-view filtering.

[0032] S32. Based on the phase-velocity mapping relationship, obtain the multi-view HLOS flow velocity. The formula is as follows:

[0033] (3)

[0034] In the formula: This refers to the baseline length between the two channels of the oblique-looking ATI-SAR payload. For the first An angle of incidence in a line of sight. This represents the interference phase corresponding to the line of sight.

[0035] This technical solution is used to achieve the inversion of multi-view HLOS current velocity. Specifically, subpixel-level registration ensures a high degree of spatial matching between the two channel images; interferometric phase is formed to extract phase change information caused by ocean surface motion; channel phase deviation correction eliminates errors caused by differences in channel characteristics, ensuring the accuracy of the interferometric phase; multi-view filtering reduces noise interference through averaging, improves the quality of the interferometric phase, and finally obtains a reliable interferometric phase; current velocity inversion is performed based on the phase-velocity mapping relationship. Since the baseline length, incident angle, and interferometric phase between the two channels of the slant-view ATI-SAR payload have a specific physical relationship with the ocean surface current velocity, the obtained interferometric phase is converted into multi-view HLOS current velocity through a given formula, thereby accurately extracting the ocean surface current velocity information from the image interferometric information.

[0036] According to an embodiment of the present invention, in step S32, the HLOS flow rate calculated in formula (3) is... For the projection of the radial LOS velocity onto the horizontal plane, to calculate the LOS velocity, formula (3) should not contain the following: item.

[0037] According to an embodiment of the present invention, the solution of the overdetermined equations of the vector flow in step S4 includes the following specific steps:

[0038] S41. Based on observation geometry, establish a right-handed coordinate system with the x-axis as the intersection with the orbital direction, the y-axis as the direction along the orbital direction, and the z-axis as the vertical direction, and define the following parameters:

[0039] For the first The angle between the HLOS velocity in each view and the x-axis; For the first An angle of incidence in one direction of view; The angle of incidence is the angle of incidence from the side view direction; For the first The angle between the viewing direction and the side viewing direction;

[0040] S42. According to the view geometry, the parameters satisfy the following relationship:

[0041] (4)

[0042] (5)

[0043] S43, HLOS flow rate for each view direction With the ocean vector velocity to be determined Establish a linear relationship, where, For the cross-track component, Let the component be along the orbital direction, then:

[0044] (6)

[0045] make:

[0046] (7)

[0047] In the formula: n represents the total number of n sets of view sub-equations;

[0048] The resulting overdetermined equations are as follows:

[0049] (8)

[0050] The vector velocity is obtained by solving the least squares method. .

[0051] This technical solution transforms multi-view observation data into a solvable set of equations to obtain ocean vector currents. Specifically, a right-handed coordinate system is established based on observation geometry, and various parameters are clearly defined. These parameters precisely describe the angles between the HLOS velocities and the coordinate axes, as well as the angles of incidence, for different viewpoints. The relationships between these parameters are determined based on viewpoint geometry, ensuring that the established model conforms to actual observation conditions. A linear relationship is established between the HLOS velocities of each viewpoint and the ocean vector current velocity to be determined, transforming the complex ocean current velocity observation problem into a linear equation problem. By integrating n sets of viewpoint sub-equations, an overdetermined equation is formed. Overdetermined equations mean that the number of equations exceeds the number of unknowns, providing richer information constraints. Finally, the least squares method is used to solve this overdetermined equation. The least squares method effectively reduces the influence of observation errors and finds the vector current velocity that best matches the observation data among numerous solutions, thereby accurately reproducing the ocean vector current.

[0052] According to one embodiment of the present invention, the internal consistency check of the vector current in step S5 includes: projecting the obtained ocean vector current back onto any line of sight to obtain the estimated HLOS velocity, and comparing it with the HLOS velocity in the corresponding line of sight. The external consistency check of the vector current in step S5 includes: comparing it with independent external observation signals.

[0053] In this technical solution, the internal consistency test checks whether the estimated HLOS velocity differs significantly from the actual observed HLOS velocity, indicating that the vector current inversion results are logically sound and do not contain obvious calculation errors or logical contradictions. The external consistency test uses data sources including buoy observations and shipborne ADCP data; good consistency between the two indicates that the inversion method accurately captures the true characteristics of ocean currents, and the inversion results have high reliability.

[0054] To achieve the above objectives, the present invention also provides a slant-view ATI-SAR ocean vector current multi-view inversion system.

[0055] A slant-view ATI-SAR ocean vector current multi-view inversion system includes the following modules:

[0056] Sub-aperture and imaging module, used to divide the original echo into multiple line-of-sight sub-apertures according to the multi-center Doppler frequency and sub-band width and focus them independently, outputting two-channel SLC image pairs of different line-of-sight;

[0057] The ATI processing module is used to perform track-to-track interferometry on each line-of-sight SLC image pair and obtain the corresponding HLOS flow rate.

[0058] The vector solution module is used to output ocean vector current results;

[0059] The quality control module is used to verify the internal and external consistency of ocean vector current results.

[0060] In this technical solution, the sub-aperture and imaging module receives the raw echo signal from the slant-viewing ATI-SAR payload. Since the raw echo signal contains various noises and interferences, it is meticulously divided using a pre-set multi-center Doppler frequency and sub-band width. Echo signals from different viewing directions exhibit different Doppler characteristics due to varying observation angles; this division separates the signals from different viewing directions, forming multiple viewing direction sub-apertures. Each viewing direction sub-aperture undergoes independent focusing processing, and the echo signal is converted into an image using an imaging algorithm, ultimately outputting two-channel SLC image pairs for different viewing directions. The ATI processing module receives the viewing direction SLCs output by the sub-aperture and imaging module. For image pairs, along-track interferometry is performed. First, subpixel-level registration is conducted to ensure precise spatial alignment of the two channels. Then, an interferometric phase is formed through complex calculations, containing information about minute changes caused by ocean surface motion. Channel phase deviations are corrected to eliminate errors caused by differences in channel characteristics. Multi-view filtering is performed to reduce noise interference and improve the quality of the interferometric phase, thereby obtaining the HLOS current velocity for each view direction. After obtaining the HLOS current velocity for each view direction from the ATI processing module, the vector solution module uses algorithms to process the unidirectional velocity information. Considering the geometric relationships between different view directions and the physical characteristics of ocean currents, the HLOS current velocities for multiple view directions are converted into two-dimensional ocean vector flow results by solving overdetermined equations, thus comprehensively describing the flow state of the ocean surface. The quality control module rigorously verifies the ocean vector current results output by the vector solution module. For internal consistency verification, the obtained ocean vector current is back-projected onto any line of sight to obtain the estimated HLOS velocity, which is then compared and evaluated with the HLOS velocity actually observed in that line of sight. For external consistency verification, the inversion results are compared and evaluated with independent external observation signals to ensure the accuracy of the final output ocean vector current results.

[0061] Compared with the prior art, the present invention has the following advantages:

[0062] (1) The invention uses non-orthogonal side-view observation for the payload, which enhances the observability of the along-track component by using physical oblique view, while maintaining the low cost of single beam and system simplicity. Since the contribution of the azimuth component is proportional to the sine of the oblique view angle, the invention can obtain a much larger along-track component than the "virtual oblique view", which improves the solvability of the equation and reduces the inversion instability. The invention exchanges a small system burden for intuitive and reliable observation information, saves equipment investment, enables large-scale on-orbit observation of vector flow, and is easy to implement in engineering.

[0063] (2) The invention divides the original echo sub-band during imaging, flexibly sets the line of sight, and reduces errors; it solves the vector flow to construct an overdetermined set of equations and uses least squares to reduce random errors; the invention proposes a consistency evaluation of the inversion results, which improves the reliability of the results and is of great significance to meteorological and oceanographic research.

[0064] (3) The three-step closed-loop processing of this invention resolves the bottleneck of traditional technology, makes breakthroughs in engineering usability and result robustness, and fills the gap in reliable observation and inversion technology of single-beam ATI-SAR vector flow. Attached Figure Description

[0065] Figure 1 This is a flowchart illustrating the principle of the method of the present invention.

[0066] Figure 2 This is a schematic diagram of the principle connection of the present invention.

[0067] Figure 3 This is a schematic diagram of the observation geometry of the oblique-view ATI-SAR payload device. Detailed Implementation

[0068] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0069] Example 1

[0070] like Figure 1 and Figure 2 As shown, this invention provides a multi-line-of-sight inversion system for oblique-view ATI-SAR ocean vector currents, comprising the following modules:

[0071] Sub-aperture and imaging module, used to divide the original echo into multiple line-of-sight sub-apertures according to the multi-center Doppler frequency and sub-band width and focus them independently, outputting two-channel SLC image pairs of different line-of-sight;

[0072] The ATI processing module is used to perform track-to-track interferometry on each line-of-sight SLC image pair and obtain the corresponding HLOS flow rate.

[0073] The vector solution module is used to output ocean vector current results;

[0074] The quality control module is used to verify the internal and external consistency of ocean vector current results.

[0075] In this technical solution, the sub-aperture and imaging module receives the raw echo signal from the slant-viewing ATI-SAR payload. Since the raw echo signal contains various noises and interferences, it is meticulously divided using a pre-set multi-center Doppler frequency and sub-band width. Echo signals from different viewing directions exhibit different Doppler characteristics due to varying observation angles; this division separates the signals from different viewing directions, forming multiple viewing direction sub-apertures. Each viewing direction sub-aperture undergoes independent focusing processing, and the echo signal is converted into an image using an imaging algorithm, ultimately outputting two-channel SLC image pairs for different viewing directions. The ATI processing module receives the viewing direction SLCs output by the sub-aperture and imaging module. For image pairs, along-track interferometry is performed. First, subpixel-level registration is conducted to ensure precise spatial alignment of the two channels. Then, an interferometric phase is formed through complex calculations, containing information about minute changes caused by ocean surface motion. Channel phase deviations are corrected to eliminate errors caused by differences in channel characteristics. Multi-view filtering is performed to reduce noise interference and improve the quality of the interferometric phase, thereby obtaining the HLOS current velocity for each view direction. After obtaining the HLOS current velocity for each view direction from the ATI processing module, the vector solution module uses algorithms to process the unidirectional velocity information. Considering the geometric relationships between different view directions and the physical characteristics of ocean currents, the HLOS current velocities for multiple view directions are converted into two-dimensional ocean vector flow results by solving overdetermined equations, thus comprehensively describing the flow state of the ocean surface. The quality control module rigorously verifies the ocean vector current results output by the vector solution module. For internal consistency verification, the obtained ocean vector current is back-projected onto any line of sight to obtain the estimated HLOS velocity, which is then compared and evaluated with the HLOS velocity actually observed in that line of sight. For external consistency verification, the inversion results are compared and evaluated with independent external observation signals to ensure the accuracy of the final output ocean vector current results.

[0076] Example 2

[0077] In practical applications, such as Figure 1 As shown, this embodiment provides a method for ocean vector current inversion using oblique-looking ATI-SAR multi-view sub-aperture focusing, including the following steps:

[0078] S1. Observation of the oblique-looking ATI-SAR payload: Based on the oblique-looking ATI-SAR payload device carried by the satellite, electromagnetic waves are emitted towards the same ocean surface along the flight direction, and the original echo signals of the two channels after being reflected by the ocean surface are observed.

[0079] like Figure 3 As shown, the physical angle of view of the selected oblique-looking ATI-SAR payload is 4.6° and the beam opening angle is 2.4°, which significantly improves the observability of the azimuth velocity component.

[0080] S2. Multi-view sub-aperture focusing: Based on the multi-center Doppler frequency and sub-band width, the original echo signal is divided into multiple view sub-apertures and focused independently, outputting two-channel SLC image pairs with different view directions;

[0081] Assuming the Doppler center frequency of the original echo signal The Hz frequency is 1109 Hz, and the center viewing angle is 4.6° ± 0°. Preferably, 12 angle groups are selected within the range of -0.8° to -1.2° and +0.8° to +1.2°. According to formula (1), the calculation of the first digit under a given viewing angle is obtained. The angle between the aperture view and the frontal / side view:

[0082] (1)

[0083] In the formula: The physical angle of view of the beam. For the first The angle of view of each aperture relative to the beam center line of view;

[0084] S22. Based on the Doppler subband method, first perform FFT on the original echo signal along the azimuth direction; at the subband center frequency... Applying a bandpass window with a bandwidth equal to the subband width at a given point yields the corresponding subband spectrum; the subband center frequency... The formula is as follows:

[0085] (2)

[0086] In the formula: For platform speed, For the operating wavelength, For the first The angle between the line of sight and the side-view direction; the Doppler center frequency of the central line of sight. ;

[0087] Perform an FFT on the original echo along the azimuth direction; at the center frequency in each line of sight. A bandpass window with a bandwidth equal to the sub-band width is applied to obtain the corresponding sub-band spectrum. Then, an azimuth IFFT is performed on each sub-band to return to the time domain, obtaining the original "sub-data" for each line of sight. Based on the Chirp Scaling (CS) algorithm, the sub-data of each channel in each line of sight is imaged and focused to obtain multiple sets of SLC pairs corresponding to the line of sight.

[0088] S3. Inversion of HLOS velocities in multiple directions: Along-track interferometry is performed on two-channel SLC image pairs with different directions to obtain the interferometric phase, and the HLOS velocities in multiple directions are obtained by inversion of the interferometric phase.

[0089] Along-track interferometry (ATI) processing is performed, including sub-pixel-level registration of the two-channel SLC pair, interferometric phase formation, channel phase deviation correction, and multi-view filtering, to obtain the interferometric phase. Based on the phase-velocity mapping relationship, the HLOS flow velocity in each view direction is obtained. :

[0090] (3)

[0091] S4. Solving the overdetermined equations of the vector current: Based on the observation geometry, establish the overdetermined equations between the multi-view HLOS velocity and the vector current to be determined, and use the least squares method to solve for the ocean vector current composed of the along-track and cross-track components.

[0092] First, declare the coordinate system and parameter definitions: establish a right-handed coordinate system: the x-axis is the direction intersecting the track, the y-axis is the direction along the track, and the z-axis is the vertical direction.

[0093] For the first The angle between the HLOS velocity in each view and the x-axis; For the first An angle of incidence in one direction of view; The angle of incidence is the angle of incidence from the side view direction; For the first The angle between the viewing direction and the side viewing direction;

[0094] According to the line-of-sight geometry, the above angles satisfy the following relationship:

[0095] (4)

[0096] (5)

[0097] HLOS flow rate for each view With the ocean vector velocity to be determined Establish a linear relationship, where, For the cross-track component, Let the component be along the orbital direction, then:

[0098] (6)

[0099] make:

[0100] (7)

[0101] In the formula: n represents the total number of n sets of view sub-equations;

[0102] The resulting overdetermined equations are as follows:

[0103] (8)

[0104] In the formula: the subscript n indicates that there are n sets of line-of-sight sub-equations. In this embodiment, n=12. The vector velocity is obtained by solving the least squares method. .

[0105] S5. Verification of Internal and External Consistency of Vector Flow: The internal consistency verification includes: projecting the obtained vector flow back onto the central line of sight to obtain the estimated HLOS velocity and comparing it with the HLOS velocity in that line of sight; the deviation is 0.04 m / s. The external consistency verification includes: comparing and evaluating with independently observed GNSS buoy data; the velocity direction deviation is 5.46°, and the velocity magnitude deviation is 0.07 m / s. Therefore, the inversion results of this embodiment achieve good internal and external consistency, indicating that the vector flow inversion method of this patent can obtain good inversion accuracy.

[0106] In this specification, the present invention has been described with reference to specific embodiments. These embodiments are preferred embodiments of the present patent and are not intended to limit the scope of the invention. It should be noted that the present invention is not limited to the specific embodiments described above. Improvements, variations, combinations, substitutions, etc., made by those skilled in the art without departing from the principles of the present invention are all within the scope of protection claimed in the claims of the present invention.

Claims

1. A method for ocean vector current inversion using oblique-looking ATI-SAR multi-view sub-aperture focusing, characterized in that, Includes the following steps: S1. Observation of the oblique-looking ATI-SAR payload: Based on the oblique-looking ATI-SAR payload device carried by the satellite, electromagnetic waves are emitted towards the same ocean surface along the flight direction, and the original echo signals of the two channels after being reflected by the ocean surface are observed. S2. Multi-view sub-aperture focusing: Based on the multi-center Doppler frequency and sub-band width, the original echo signal is divided into multiple view sub-apertures and focused independently, outputting two-channel SLC image pairs with different view directions; S3. Inversion of HLOS velocities in multiple directions: Along-track interferometry is performed on two-channel SLC image pairs with different directions to obtain the interferometric phase, and the HLOS velocities in multiple directions are obtained by inversion of the interferometric phase. S4. Solving the overdetermined equations of the vector current: Based on the observation geometry, establish the overdetermined equations between the multi-view HLOS velocity and the vector current to be determined, and use the least squares method to solve for the ocean vector current composed of the along-track and cross-track components. S5. Verification of internal and external consistency of vector currents: Perform internal and external consistency verification on the obtained ocean vector currents and output the evaluation inversion results.

2. The ocean vector current inversion method using oblique-looking ATI-SAR multi-view sub-aperture focusing as described in claim 1, characterized in that, In step S1, the observation of the slant-look ATI-SAR payload is performed with a physical slant angle greater than 3°, which is used to enhance the observability of the azimuth velocity component.

3. The ocean vector current inversion method using oblique-looking ATI-SAR multi-view sub-aperture focusing as described in claim 1, characterized in that, The multi-view aperture focusing in step S2 includes the following specific steps: S21. Assume the Doppler center frequency of the original echo signal is... Calculate the first [value] under a given viewing angle. The angle between the aperture view and the frontal / side view The formula is as follows: （1） In the formula: The physical angle of view of the beam. For the first The angle of view of each aperture relative to the beam center line of view; S22. Based on the Doppler subband method, first perform FFT on the original echo signal along the azimuth direction; at the subband center frequency... Applying a bandpass window with a bandwidth equal to the subband width at a given point yields the corresponding subband spectrum; the subband center frequency... The formula is as follows: （2） In the formula: For platform speed, For the operating wavelength, For the first The angle between the line of sight and the side-view direction; the Doppler center frequency of the central line of sight. ; Then, an azimuth IFFT is performed on each sub-band to return to the time domain, obtaining the original sub-data for each line of sight; S23. Based on the Chirp Scaling algorithm, the original sub-data of each viewing direction is imaged and focused to output two-channel SLC image pairs of different viewing directions.

4. The ocean vector current inversion method using oblique-looking ATI-SAR multi-view sub-aperture focusing as described in claim 3, characterized in that, The two-channel SLC image pairs with different viewing directions in step S23 include: The center line of sight SLC1, line of sight 1 SLC1, line of sight 2 SLC1, up to line of sight n SLC1 in channel 1; The center line of sight SLC2, line of sight 1 SLC2, line of sight 2 SLC2, up to line of sight n SLC2 in channel 2; Wherein: center view SLC1 and center view SLC2 are one SLC image pair; view 1 SLC1 and view 1 SLC2 are one SLC image pair; view 2 SLC1 and view 2 SLC2 are one SLC image pair, and so on, until view n SLC1 and view n SLC2 are one SLC image pair.

5. The ocean vector current inversion method using oblique-looking ATI-SAR multi-view sub-aperture focusing as described in claim 4, characterized in that, The inversion of multi-view HLOS flow velocity in step S3 includes the following specific steps: S31. For two-channel SLC images with different viewing directions, the interference is processed along the track. The interference is obtained by sub-pixel level registration, forming interference phase, channel phase deviation correction and multi-view filtering. S32. Based on the phase-velocity mapping relationship, obtain the multi-view HLOS flow velocity. The formula is as follows: （3） In the formula: This refers to the baseline length between the two channels of the oblique-looking ATI-SAR payload. For the first An angle of incidence in a line of sight. This represents the interference phase corresponding to the line of sight.

6. The ocean vector current inversion method using oblique-looking ATI-SAR multi-view sub-aperture focusing as described in claim 5, characterized in that, In step S32, the HLOS velocity calculated in formula (3) For the projection of the radial LOS velocity onto the horizontal plane, to calculate the LOS velocity, formula (3) should not contain the following: item.

7. The ocean vector current inversion method using oblique-looking ATI-SAR multi-view sub-aperture focusing as described in claim 6, characterized in that, The solution of the overdetermined equations for the vector flow in step S4 includes the following specific steps: S41. Based on observation geometry, establish a right-handed coordinate system with the x-axis as the intersection with the orbital direction, the y-axis as the direction along the orbital direction, and the z-axis as the vertical direction, and define the following parameters: For the first The angle between the HLOS velocity in each view and the x-axis; For the first An angle of incidence in one direction of view; The angle of incidence is the angle of incidence from the side view direction; For the first The angle between the viewing direction and the side viewing direction; S42. According to the view geometry, the parameters satisfy the following relationship: （4） （5） S43, HLOS flow rate for each view direction With the ocean vector velocity to be determined Establish a linear relationship, where, For the cross-track component, Let the component be along the orbital direction, then: （6） make: （7） In the formula: n represents the total number of n sets of view sub-equations; The resulting overdetermined equations are as follows: （8） The vector velocity is obtained by solving the least squares method. .

8. The ocean vector current inversion method using oblique-looking ATI-SAR multi-view sub-aperture focusing as described in claim 7, characterized in that, The internal consistency check of the vector current in step S5 includes: projecting the obtained ocean vector current back onto any line of sight to obtain the estimated HLOS velocity, and comparing and evaluating it with the HLOS velocity of the corresponding line of sight.

9. The ocean vector current inversion method using oblique-looking ATI-SAR multi-view sub-aperture focusing as described in claim 7, characterized in that, The verification of the internal and external consistency of the vector flow in step S5 includes the external consistency verification, which involves comparing and evaluating the data with independent external observation signals.

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