External Calibration Processing Method of Airborne SAR Radiation Based on Weakly Arranged Corner Reflectors

Abstract

The invention relates to an airborne SAR radiation external calibration processing method based on weak arrangement of corner reflectors. The method comprises the following steps: obtaining original SAR image data of a calibration field; on the basis of a point target radar equation, reconstructing an radiation external calibration equation; performing stable estimation on calibrator image energy and geometric optical solution on a calibration RCS; carrying out fitting and correcting on a radar system transfer function to obtain preliminary radiation calibration SAR image data; carrying out the stable estimation on the calibrator image energy and the geometric optical solution on the calibration RCS; and estimating a system constant item so as to generate calibration data and obtain final radiation calibration SAR image data. According to the invention, on the basis of the point target radar equation, according to the characteristic of parameters of a radar system, the SAR radiation external calibration equation comprising a change system transfer function and a constant system constant item is reconstructed, the application process of radiation external calibration is simplified, and the problem is avoided that it is quite difficult for airborne SAR flight to obtain a large-scope homogeneous stable tropical rainforest area frequently used by similar spaceborne SAR radiation calibration.

Description

technical field [0001] The invention relates to the technical field of airborne synthetic aperture radar SAR data processing, in particular to an airborne SAR external calibration processing method based on weakly arranged corner reflectors. Background technique [0002] The purpose of SAR radiation calibration is to establish the correct correspondence between the intensity value of each image pixel and the real backscattering coefficient of the target in the obtained SAR image, so that the SAR image intensity can be accurately correlated with the physical parameters of the observed target, which is beneficial to Quantitative applications of SAR data. According to whether the external calibration reference target of the SAR system needs to be used in the calibration process, SAR radiation calibration can generally be divided into internal calibration and external calibration. Radiation external calibration is better than internal calibration in that it directly measures end...

AI Technical Summary

Problems solved by technology

Compared with placing the background area, the point target requires a fairly large and known radar cross-section in advance, common angular reflectors, radar transponders, etc., the current angular reflector generally uses the maximum RCS value as the known value, so It is necessary to adjust the azimuth and elevation angles of each corner reflector according to the flight path of the airborne platform and the radar incident angle. However, due to the change of the radar incident angle from the distance upward and the flight instability of the airborne SAR platform, it is actually necessary to achieve precise adjustment. At the same time, due to the difference in the degree of focus of the SAR system and the resolution of the image, the point target does not appear as a single strong pixel on the SAR image, but often appears as a collection of multiple strong pixels, thus bringing The difference between the point target pixel peak and the actual point target image energy affects the calibration accuracy

Generally, distributed targets should have stable backscattering, time-invariant, and isotropic properties, such as tropical rain forests, large areas of uniform grassland, etc. Compared with spaceborne SAR, due to the limited flight range of airborne SAR, it is generally difficult to obtain Tropical rainforest is a large-scale distribution target with known scattering characteristics and stability, while the use of other distribution targets such as grassland and vegetation with unknown stability will reduce the accuracy of SAR external radiation calibration

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