对ENVISAT ASAR level2算法固有误差的分析
Analysis on intrinsic error of ENVISAT ASAR level 2 algorithm
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摘要: 欧洲空间局的ENVISAT ASAR level 2算法是从合成孔径雷达(SAR)单视复图像反演涌浪方向谱的算法.该算法假设双峰海浪谱的SAR图像交叉谱是涌浪的图像交叉谱和风浪的图像交叉谱之和.实际上双峰海浪谱的SAR图像交叉谱中还有一个混合项,正是该混合项导致ENVI-SAT ASAR level 2算法有固有误差.利用遥感仿真的方法分析了不同海况条件下该算法的这一固有误差,结果表明,只有在有效波高较小、或风浪的成分较少、或双峰海浪的传播方向较靠近SAR距离向、或波长较长时固有误差才较小,ENVISAT ASAR level 2算法对海浪谱的反演才较为适用.
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关键词:
- 合成孔径雷达 /
- 海浪谱 /
- ENVISATASARlevel2算法 /
- 误差分析
Abstract: ENVISAT ASAR level 2 algorithm developed by the European Space Agency(ESA) provides directional ocean wave spectra retrieved from synthetic aperture radar(SAR) single look complex data.This inversion algorithm is based on approximating the total SAR cross-spectrum as a sum of a quasilinear part due to the swell and a nonlinear part due to the wind sea.How ever,this assumptionomits a mixed term which brings the intrinsic error to the ENVISAT ASAR level 2 algorithm.Ananalysis is made on the intrinsic error by inverting the simulated SAR cross-spectra using the EN VISAT ASAR level 2 algo rithm.The dependence of the intrinsic error on the ocean wave condition is discussed.It is shown that the ENV-I SAT ASAR level 2 algo rithm can provide the accept able results only when the ocean waves have a smaller significant wave height,or a smaller wind wave component,or a wave direction closer to the SAR range direction,or a longer wavelength. -
European Space Agency.ASAR Product Handbook Issue 2.2[M/OL].http://envisat.esa.int/handbooks/asar/CNTR.htm.2007. JOHNSEN H,CHAPRON B,WALKER N,et al.The ASAR wave mode:Level 1 and 2 algorithms and products[C/CD]//Proceedings of the Envisat Calibration Review.Noordwijk:ESA Publications Division,2002. COLLARD F,ARDHUIN F,CHAPRON B.Extraction of coastal ocean wave fields from SAR images[J].IEEE Journal of Oceanic Engineering,2005,30(3):526-533. JOHNSEN H,ENGEN G,CHAPRON B.Validation of ASAR wave mode level 2 product[C]//Proceedings of IEEE International Geoscience and Remote Sensing Symposium.Toulouse:IEEE Press,2003:1127-1129. KERBAOL V,JOHNSEN H,CHAPRON B,et al.Quality assessment of ENVISAT ASAR wave mode products based on regional and seasonal comparisons with WAM model outputs[C/CD]//Proc 2004 Envisat & ERS Symposium.Noordwijk:ESA Publications Division,2005. 王贺,杨劲松,黄韦艮,等.双峰海浪谱的SAR图像交叉谱仿真研究[J].遥感技术与应用,2007,22(2):291-296. ENGEN G,JOHNSEN H.SAR-ocean wave inversion using image cross spectra[J].IEEE Tran Geosci Remote Sens,1995,33(4):1047-1056. -
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