Two-dimensional Nonlinear Frequency Modulation Method for SAR Imaging in Geosynchronous Orbit

Abstract

The invention discloses a two-dimensional non-linear frequency conversion and modulation method for SAR imaging of a geosynchronous orbit. By means of the two-dimensional non-linear frequency conversion and modulation method, imaging processing of GEO SAR large-scale scene echoes can be effectively completed. According to the two-dimensional non-linear frequency conversion and modulation method, firstly, a GEO SAR space variation model is established, wherein focusing parameters, namely secondary changes of the second-order coefficient in the distance direction and the azimuth direction during slope distance history 4-order Taylor series expansion of a radar and linear changes of the third-order coefficient in the azimuth direction, in the SAR imaging processing process are considered in the model; secondly, NCS imaging processing in the distance direction and NCS imaging processing in the azimuth direction are conducted according to the space variation model. Compared with the prior art, by means of the two-dimensional non-linear frequency conversion and modulation method, imaging processing of the GEO SAR large-scale scene echoes can be effectively completed, phase errors, caused by two-dimensional space variation of the parameters, in the azimuth direction are eliminated, accurate focusing in the azimuth direction can be completed, and imaging of the GEO SAR large-scale scene (400 km * 400 km) can be realized.

Description

technical field [0001] The invention relates to the technical field of synthetic aperture radar imaging, in particular to a two-dimensional nonlinear frequency modulation method for geosynchronous orbit SAR imaging. Background technique [0002] Geosynchronous Orbit Synthetic Aperture Radar (GEOSAR) is a Synthetic Aperture Radar (SAR) system operating on satellites in geosynchronous orbit at an altitude of 36,000km above the ground. Since GEOSAR can cover an area of ​​more than 1000km, and the revisit period for key areas can be less than 1 day, GEOSAR has great practical value in land detection, soil moisture detection, atmospheric water vapor mapping, and surface deformation detection. [0003] Due to the high orbital height of GEOSAR, non-zero eccentricity, small satellite velocity, long synthetic aperture time, and large observation range, the imaging focusing parameters have not only distance-to-space variability, but also azimuth-to-space variability, so effective Ima...

AI Technical Summary

Problems solved by technology

In the traditional GEOSAR imaging algorithm, the nonlinear frequency modulation (NCS) algorithm is a relatively accurate imaging algorithm, but because the azimuth and space variability of GEOSAR imaging parameters are ignored, the imaging scene and imaging resolution are restricted.

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