89 GHz多入射角亮温差反演海冰密集度的可行性分析

Feasibility analysis of retrieving sea ice concentration by multi-incidence angle brightness temperature at 89 GHz

被动微波遥感是目前进行海冰密集度观测的重要方式,ASI(ARTIST Sea Ice algorithm)算法利用AMSR-E的89 GHz双极化亮温可获得目前海冰密集度(SIC)产品中最高空间分辨率6.25 km,但是需要低频数据进行大气校正。本文提出一种基于89 GHz综合孔径辐射计单频多角度观测亮温反演海冰密集度的新方法,并开展了可行性分析。该方法利用多入射角亮温信息弥补观测过程中海冰与海水亮温信息的混淆,提高SIC的反演精度,并且可以实现高空间分辨率。首先构建了星载观测海冰辐射亮温仿真系统,利用仿真亮温数据及FY-3C星微波湿度计89 GHz通道实测亮温数据,开展89 GHz亮温角度敏感性分析;其次,推导建立了基于89 GHz角度亮温差的SIC反演算法,结合欧洲中期天气预报中心(ECMWF)的SIC产品及亮温仿真系统完成了初步反演验证。验证结果表明,利用入射角亮温差可以实现海冰密集度的反演,利用多组入射角组合进行最小均方根加权平均后处理可以最大程度的降低SIC的反演误差。输入的高斯白噪声为2 K时,可以获得5%的SIC误差。最终结果证明利用连续角度亮温差进行SIC反演,可以充分扩大海水与海冰的区分。

Passive microwave remote sensing is an important method for observing the sea ice concentration(SIC).The ASI(ARTIST Sea Ice algorithm)can obtain the highest spatial resolution of 6.25 km2in the current SIC products by using the dual-polarized brightness temperature of AMSR-E at 89 GHz.However,additional auxiliary low-frequency band data are still needed for weather filter.In this work,a new SIC retrieving algorithm based on single-frequency multi-incident angle brightness temperature data has been proposed and studied,which can be applied on an 89 GHz synthetic aperture radiometer.Fully utilizing the multi-incident angle brightness temperature with a synthetic aperture radiometer can separate the information of sea ice and seawater,improve the precision of SIC retrieving,and achieve high spatial resolution.The first step involves creating a simulation system for space-borne observation of sea–ice radiant brightness temperature and using the measured data of the 89 GHz channel from the FY-3C/MWHS to carry out the sensitivity analysis between brightness temperature and angle at 89 GHz.The second step consists of developing an SIC retrieving algorithm based on the angle brightness temperature difference at 89 GHz and completing the preliminary retrieving verification by combining the SIC product of ECMWF and the brightness temperature simulation system.The results show that the SIC retrieval can be realized by using the incident angle brightness temperature difference.Moreover,the minimum root mean square weighted average post-processing by using the combination of multi-incidence angle can minimize the retrieving error of SIC.When the input Gaussian white noise is 2 K,5%SIC error can be obtained.The final results show that the SIC retrieval with the combination of multi-incidence angle can fully expand the distinction between sea water and sea ice.