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A New Method for Doppler-Ambiguity-Number Estimation in Spaceborne SAR Imaging

ZHAI Wenshuai,ZHANG Yunhua (Center for Space Science and Applied Research,Chinese Academy of Sciences,Beijing 100080,China)  
It is found that in the Chirp Scaling algorithm,the curvature factor Cs and the effective FM chirp rate Ks are very sensitive to the change of Doppler-Ambiguity-Number(DAN).When DAN is inaccurate,Cs and Ks will be invalid and the definition of resulted SAR image will degrade,i.e.the definition-evaluation-function of SAR image(entropy or mean variance) varies with DAN.Based on the analysis,a new method was proposed for DAN estimation in spaceborne SAR imaging by finding the minimum of image entropy or the maximum of image mean variance.The raw data of Radarsat were used to validate the method.The results indicate that the algorithm based on mean variance is better than the algorithm based on entropy.The former is applicable no matter the contrast of image area is high or low,but the latter is only suitable for high contrast area.
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