Low-frequency broadband satellite-borne SAR imaging ionosphere phase error compensation method

Abstract

The invention provides a low-frequency broadband satellite-borne SAR imaging ionosphere phase error compensation method, which is characterized in that series decomposition is carried out on ionosphere phase error to three terms based on Legendre orthogonal basis, and the obtained errors are mutually orthogonal, so that the problem of order coupling of an existing assessment method is solved; then, based on an expression of each order derived based on an orthogonal model, influence of zero-order phase error on broadening of direction images, first-order phase error on translation of distance images, on pulse broadening caused by second-order phase error and on pulse distortion caused by third-order phase error are quantitatively evaluated; and based on the influence, ionosphere total electron content TEC information can be obtained, and ionosphere influence compensation can be carried out on the images. The method can accurately reflect the influence of true ionosphere phase error on low-frequency broadband satellite-borne SAR imaging, and thus ionosphere influence compensation precision is improved.

Description

technical field [0001] The invention relates to a low-frequency broadband spaceborne SAR imaging ionospheric phase error compensation method, which belongs to the field of synthetic aperture radar and ionospheric wave propagation, and is mainly used for improving the ionospheric compensation accuracy of low-frequency broadband spaceborne SAR imaging. Background technique [0002] Focusing on the global demand for high-resolution identification of forest vegetation and underground hidden targets, one of the development trends of low-frequency spaceborne Synthetic Aperture Radar (SAR) systems operating in the VHF / UHF frequency band is to move towards a larger Relative bandwidth design. However, because it works on or in the ionosphere, the echo phase of these frequency bands is inevitably affected, and the lower the carrier frequency and the larger the bandwidth, the more serious the impact, which makes the performance of the SAR system drop sharply. In order to suppress the ...

AI Technical Summary

Problems solved by technology

With the increase of the bandwidth, because the existing method does not consider the zero-order component in the quadratic phase error, it cannot well compensate the influence of the zero-order phase error

[0005] Second, a phase error will cause the image to shift in distance. Although for a single point in the scene, the image shift will not affect the image quality, but the actual scene is composed of many point targets, and this shift will cause a decrease in local resolution.

As the bandwidth increases, the existing compensation method does not consider the first-order component of the third-order phase error, so it will also lead to a non-negligible error

[0006] Third, the quadratic phase error will cause the range-to-pulse broadening (after the pulse pressure), resulting in a decrease in resolution. Since the quadratic phase error evaluated by the existing method contains a zero-order term, its accuracy needs to be improved

[0007] Fourth, the three-time phase error will cause asymmetric distortion after the range pulse pressure. For narrow-band systems such as PALSAR or BIOMASS SAR, the magnitude of the three-time phase error is very small and can be ignored

However, when analyzing a large bandwidth, the primary component in the existing method will cause obvious errors

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