Sub-range profile offset deviation-based satellite borne SAR (Synthetic Aperture Radar) ionosphere calibration method

Abstract

The invention provides a sub-range profile offset deviation-based satellite borne SAR (Synthetic Aperture Radar) ionosphere calibration method, which eliminates the limitation to a sampling rate while eliminating the influence of a non-ideal matrix envelope and improves the robustness of ionosphere TEC (Total Electron Content) measuring accuracy. The method comprises the following steps: 1, decomposing a strong scattering point target signal or an active calibrator signal into two upper and lower sub-band pulse signals by using a low-pass filter and a high-pass filter; 2, compressing distance of the upper and lower sub-band pulse signals; 3, mutually correlating upper and lower sub-range profile envelopes to obtain a normalized mutual correlation energy spectrum; and 4, extracting a phase spectrum of the normalized mutual correlation energy spectrum in the third step, obtaining an estimated value of delta t shift by estimating the slope for change of the phase along with frequency f, and further obtaining an estimated value of the ionosphere TEC, wherein the sub-range profile offset deviation generated by ionosphere is at a sub-pixel level, i.e., the delta t shift is less than 1 / fs, fs represents a radar sampling rate, and the phase wrapping of the normalized mutual correlation energy spectrum is avoided.

Description

technical field [0001] The invention relates to a spaceborne SAR ionospheric calibration method based on sub-range image offset difference, which relates to the field of synthetic aperture radar (SAR) signal processing, in particular to the field of spaceborne synthetic aperture radar ionospheric calibration. Background technique [0002] The ionosphere is the partially ionized region of the Earth's atmosphere, extending from about 50 km above the ground to about 1000 km. Spaceborne SAR works at a satellite orbit altitude of 500km to 800km, and the spaceborne SAR signal passes through the ionosphere twice, which inevitably produces amplitude and phase distortion. Among them, the ionospheric group delay effect causes the SAR image distance shift, the ionospheric dispersion effect causes the SAR image range resolution to decrease, and the ionospheric fluctuation causes the SAR image azimuth resolution to deteriorate. In addition, the above three effects will destroy the phase...

AI Technical Summary

Problems solved by technology

[0008] 2) Spaceborne SAR and active scalers record digital signals, and the measurement accuracy of pulse time width is limited by the sampling rate of the equipment

[0009] 3) Affected by noise, the time envelope of the spaceborne SAR signal will degrade to a certain extent

[0010] In summary, the spaceborne SAR ionospheric calibration based on the comparison of the pulse time width of the transmitted signal and the received signal has high requirements on the performance of the spaceborne SAR radar, and there are many error sources, and its practicability still needs to be improved.

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