CN-122017831-A - Satellite-borne SAR self-focusing method, system, computer and storage medium for long-time integral beam-focusing mode

CN122017831ACN 122017831 ACN122017831 ACN 122017831ACN-122017831-A

Abstract

The invention discloses a satellite-borne SAR self-focusing method, a system, a computer and a storage medium aiming at a long-time integral beam-focusing mode, which are used for realizing range migration error estimation of a partial region by screening a strong scattering target region in a mode of taking maximum contrast or maximum power as a target and applying a minimum entropy range alignment algorithm based on a partial frequency spectrum according to the divided grid size, the full-scene range migration error estimation is realized by combining hample filtering and polynomial fitting, the phase error estimation of the partial region is realized by a minimum entropy phase correction algorithm, the phase error estimation of the full scene is realized by combining a Savitzky-Golay filter and polynomial fitting, the range migration error and the phase error estimation result of the full scene are applied, the unified compensation processing is carried out on the original full-scene image, and the fine focusing of the full scene is realized. The invention can realize the fine focusing of the full view of the large scene under the condition of ultra-long synthetic aperture time of more than 15 seconds.

Inventors

WEN XUEJIAO
QIU XIAOLAN
CHEN WEIDONG

Assignees

苏州空天信息研究院

Dates

Publication Date: 20260512
Application Date: 20251128

Claims (10)

1. The satellite-borne SAR self-focusing method for the long-time integral beam-focusing mode is characterized by comprising the following steps of: Step 1, for a single-view complex image of SARL1A level, carrying out full-image blocking processing according to a set azimuth blocking size and a distance blocking size; Step 2, counting power values of any segmented image, calculating contrast of the segmented image according to power distribution in the segmented image, and sequencing the contrast of the segmented image to obtain a segmented image with the largest contrast in all the segmented images and marking the segmented image as a strong scattering area; Step 3, carrying out Fourier transform on the strong scattering region slice to obtain azimuth frequency domain data, taking out-of-band signal energy as clutter energy, screening a frequency spectrum with high signal-to-clutter ratio, adopting a minimum entropy distance alignment algorithm to obtain a full-band distance alignment curve, compensating to the azimuth frequency domain data to finish distance alignment, and simultaneously obtaining a full-scene distance migration correction curve from the full-band distance alignment curve in a polynomial fitting mode; Step 4, slicing the strong scattering region after distance alignment, performing phase self-focusing processing by applying a minimum entropy phase correction algorithm to obtain a fine focusing result and a phase compensation error of slice data of the strong scattering region, drawing a phase error compensation curve of the strong scattering region, performing high-order fitting after smoothing processing by applying a Savitzky-Golay filter to obtain a phase error compensation curve of a full-scene full-band; And 5, performing two-dimensional Fourier transform on the data of the whole scene to obtain double-frequency-domain data, performing distance envelope alignment by applying a distance migration correction curve of the whole scene, performing inverse distance Fourier transform to a distance Doppler domain, performing phase error correction on the whole frequency band by applying a phase error compensation curve of the whole frequency band of the whole scene, converting the data back to an image domain by azimuth Fourier transform, and simultaneously realizing azimuth compression to obtain a result after fine focusing.
2. The method for satellite-borne SAR self-focusing for long-time integral beam-focusing according to claim 1, wherein for any of the block images, the contrast is calculated from the power distribution inside the block, according to the following formula: ; Wherein the method comprises the steps of Represents a block image, m represents an azimuth sampling point, n represents a distance sampling point, Representing the block image statistics power value, The average value is calculated, M represents the total number of azimuth sampling points of the segmented image, and N represents the total number of distance sampling points of the segmented image; Is a constant, let it be The above method is simplified into 。
3. The method of claim 1, wherein the contrast of the segmented image is ordered to obtain a segment with the largest contrast among all segments and marked as a strong scattering region, or the average power of the segmented image is ordered to obtain a segment with the largest power among all segments and marked as a strong scattering region, wherein: the contrast of the segmented images is sequenced, and the segmented image with the largest contrast in all the segmented images is obtained and marked as a strong scattering area, so that the segmented image is suitable for scenes with more strong points, including urban areas and ports; And sorting the average power of the segmented images, and marking the segmented blocks with the largest power values in all the segmented blocks as strong scattering areas, so that the method is suitable for uniform scenes, including mountain areas and forest lands.
4. The method for satellite-borne SAR self-focusing in long-time integral beam-focusing mode according to claim 1, wherein the method is characterized in that the method comprises the steps of: Strong scattering area slices of single-view complex images are recorded as Where t represents azimuth information, The data representing the distance information and the azimuth frequency domain obtained by performing fourier transform are as follows: ; Wherein the method comprises the steps of Represents fourier transform, n represents distance-wise sampling points, m represents azimuth-wise sampling points, R represents slant-distance information of the target, λ represents wavelength, c represents light velocity, σ represents scattering intensity, And Respectively representing the residual range migration and phase error after imaging processing caused by various errors.
5. The method for satellite-borne SAR self-focusing in long-term integral beam-focusing mode according to claim 1, wherein the azimuth spectrum of the strong scattering region slice is analyzed, the out-of-band signal energy is used as clutter energy, the spectrum with high signal-to-clutter ratio is screened, and a minimum entropy distance alignment algorithm is adopted to obtain a full-band distance alignment curve The distance alignment is completed by compensating to the azimuth frequency domain data, and the specific method comprises the following steps: full-band distance alignment curve obtained by minimum entropy distance alignment algorithm The unit is pixel point, and the pixel point is converted into distance time according to the relation between the pixel point and the distance time, and the distance time is expressed as: ; Wherein the method comprises the steps of The distance direction time corresponding to the distance alignment curve is represented, hereinafter, the distance alignment curve time is referred to as a code, Representing the distance-wise sampling rate; alignment of curve time to distance Applying Hampel filter, identifying and removing abnormal value in distance alignment curve by using neutral nonlinear filtering method, and keeping basic shape unchanged to obtain filtered distance alignment curve time And then to Performing high-order fitting; Assuming that the fitting coefficient is p, the azimuth bandwidth is Ba, the pulse repetition frequency is PRF, the total number of azimuth sampling points of slice data is M, the total number of azimuth sampling points corresponding to the azimuth bandwidth is na, and the time of the distance alignment curve of the processed full frequency band is : ; Wherein the method comprises the steps of Representing a polynomial calculation function with x as a fitting coefficient, y as an independent variable and z as a sampling point number, Representing a downward rounding function; The obtained distance alignment curve time after processing Compensating into azimuth frequency domain data: ; At this time This term should be substantially corrected to zero.
6. The method of on-board SAR self-focusing for long-time integral beam focusing mode according to claim 5, wherein the distance alignment curve time obtained for the strong scattering region slice Obtaining a range migration correction curve of the whole scene by interpolation in a polynomial fitting mode And performing distance alignment processing, wherein the formula is as follows: ; Wherein, ma represents the azimuth sampling point number of the full scene data, and Na represents the azimuth sampling point number corresponding to the full field Jing Daikuan Ba.
7. The method for satellite-borne SAR self-focusing in long-time integral beam-focusing mode according to claim 6, wherein the method is characterized in that a phase error compensation curve of a strong scattering area is drawn, a Savitzky-Golay filter is applied to carry out smoothing treatment and then high-order fitting is carried out, and a phase error compensation curve of a full-scene full-band is obtained, and the specific method comprises the following steps: Is provided with For the phase error compensation curve of the strong scattering area, a Savitzky-Golay filter is applied to carry out smoothing treatment and then carry out high-order fitting, and a fitting coefficient is set as q, so that the azimuth frequency domain data of the whole scene and the azimuth frequency domain data of part of the scene have the same bandwidth and are basically equivalent to have the same frequency domain error The phase error compensation curve of the full scene full frequency band is : 。
8. A satellite-borne SAR self-focusing system for a long-time integral beam-gathering mode, wherein the satellite-borne SAR self-focusing method for the long-time integral beam-gathering mode according to any one of claims 1 to 7 is implemented to realize the satellite-borne SAR self-focusing for the long-time integral beam-gathering mode, and the method is divided into five modules respectively executing: The module 1 is used for carrying out full-image blocking processing according to the set azimuth blocking size and the distance blocking size for the SARL1A level single-view complex image; The module 2 calculates the contrast of any block image according to the power distribution in the blocks, ranks the contrast of the block images to obtain the block with the largest contrast in all the blocks and marks the block with the largest contrast as a strong scattering area, or ranks the average power of the block images to obtain the block with the largest power value in all the blocks and marks the block with the largest power value as the strong scattering area; The module 3 performs Fourier transform on the strong scattering region slice to obtain azimuth frequency domain data, takes out-of-band signal energy as clutter energy, screens a frequency spectrum with high signal-to-clutter ratio, adopts a minimum entropy distance alignment algorithm to obtain a full-band distance alignment curve, compensates the azimuth frequency domain data to complete distance alignment, and simultaneously obtains a full-scene distance migration correction curve from the full-band distance alignment curve in a polynomial fitting mode; The module 4 performs phase self-focusing processing on the slices of the strong scattering region after the distance alignment by applying a minimum entropy phase correction algorithm to obtain a fine focusing result and a phase compensation error of slice data of the strong scattering region, draws a phase error compensation curve of the strong scattering region, performs high-order fitting after smoothing processing by applying a Savitzky-Golay filter to obtain a phase error compensation curve of the whole scene and the whole frequency band; and a module 5, performing two-dimensional Fourier transform on the data of the whole scene to obtain double-frequency-domain data, performing distance envelope alignment by applying a distance migration correction curve of the whole scene, performing inverse distance Fourier transform to a distance Doppler domain, performing phase error correction on the whole frequency band by applying a phase error compensation curve of the whole frequency band of the whole scene, converting the data back to an image domain by azimuth Fourier transform, and simultaneously realizing azimuth compression to obtain a result after fine focusing.
9. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the method of spaceborne SAR self-focusing for long-time integral beaming mode of any one of claims 1-7 when the computer program is executed, to achieve spaceborne SAR self-focusing for long-time integral beaming mode.
10. A computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements the spaceborne SAR self-focusing method for long-time integral beaming mode of any one of claims 1-7, implementing the spaceborne SAR self-focusing for long-time integral beaming mode.

Description

Satellite-borne SAR self-focusing method, system, computer and storage medium for long-time integral beam-focusing mode Technical Field The invention relates to a synthetic aperture radar (SYNTHETIC APERTURE RADAR, SAR) signal processing technology, in particular to a satellite-borne SAR self-focusing method, a system, a computer and a storage medium aiming at a long-time integral beam-focusing mode. Background The spaceborne Synthetic Aperture Radar (SAR) has the advantage of being free from the limitation of climate and environment, and can continuously and stably acquire the surface information under severe weather conditions such as cloud, rain and snow, night and the like. The capability enables the ultra-high resolution spaceborne SAR to still provide important earth surface observation data [ Lan G.cumming, frank H.Wong. Synthetic aperture radar imaging, algorithm and implementation [ M ]. Electronic industry Press, 2012 ]. The ultra-high resolution on-board SAR greatly improves the precision and detail of global monitoring and provides more abundant data resources for the earth science research. The research of the ultra-high resolution space-borne SAR has important significance, not only can realize global remote sensing monitoring in all weather and all day, enhance the application capability of multiple fields such as environmental monitoring, natural resource management, disaster assessment and early warning, and the like, but also can provide key data support for urban planning, agricultural precise planting, and the like. The beamforming mode is an important way to achieve ultra-high resolution SAR. The working principle is that the radar sight line is fixed in a specific area for a long time by dynamically adjusting the direction of the antenna wave beam, and the radar can increase the synthetic aperture accumulation time of the area in the observation process, thereby obviously improving the azimuth resolution ratio. The highest resolution achieved by the currently internationally disclosed spaceborne SAR beaming modes varies among different satellite systems. For example, terraSAR-X satellites in Germany can achieve a resolution of 0.25 m in a beam-focusing mode, capella series satellites in the United states can achieve a resolution of 0.3 m in a beam-focusing mode, and the beam-focusing mode of GF3 SAR satellites in China can achieve a resolution of 0.5 m. The azimuth resolution of the beamform mode is usually positively correlated with the synthetic aperture time, which is available in low orbit satellite-borne SAR from a simple way of calculating the azimuth resolution, requiring a synthetic aperture time of 4-6 seconds to achieve the highest resolution currently known, 0.25 meters. To achieve true centimeter-level resolution, larger synthetic aperture times and finer antenna control techniques are required, resulting in long-term integration beamforming modes. At present, the mode is known to be carried on Qilu satellite I in China and is a test mode. The mode enables the radar to irradiate the target area for a longer time by prolonging the synthetic aperture time to 15-17 seconds, so that more azimuth information is acquired, and the azimuth resolution of 0.025 meters at the maximum can be realized. This prolonged gaze results in a further improvement in resolution, enabling finer surface images to be provided. Fig. 1 shows a simple geometry of a long-time integral beam-forming mode, where Ls represents the synthetic aperture length corresponding to the synthetic aperture time Ts, T represents the target point, R 0 represents the target shortest slant distance, θ is the accumulation angle of the target. In the long-time integral beam-focusing mode, SAR can achieve higher resolution due to the extension of synthetic aperture time. However, this mode is less tolerant of errors and any minor errors are amplified during the imaging process. First, in this mode, the Doppler information required for imaging is not limited to the second order Doppler tone frequency, but also includes higher order Doppler information. Conventional frequency domain imaging algorithms are highly dependent on doppler information, which can lead to severe defocusing of the image if higher order doppler information is not accurately processed. Secondly, the GPS navigation information precision requirement of the long-time integral beam-focusing mode on the satellite is extremely high, because accurate navigation information is needed in the imaging process to compensate errors caused by platform movement, and if the navigation information has errors or insufficient precision, defocusing phenomenon can occur in the image. In addition, the synthetic aperture time of the long-time integral beam-gathering mode is long, the synthetic aperture time can reach tens of seconds generally, the space-borne SAR has a long acting distance, the accumulation angle of the target in a scene can reach 5-6 degrees, and compared with