随着卫星遥感关键技术的突破,卫星光谱分辨率达到了分辨大气成分单个谱线的水平,研究人员开始了大量通道同时反演大气廓线和多种微量成分的研究。针对AIRS(Atmospheric Infrared Sounder)就红外高光谱资料反演大气水汽廓线的研究进展进行了评述,从训练数据、通道信息的提取及降维、反演算法和反演精度改进4个方面对反演晴空大气水汽廓线的研究现状进行了分析与讨论。AIRS资料反演大气水汽廓线的训练数据通常选用威斯康星大学提供的全球晴空反演训练样本集CIMSS(Cooperative Institute for Meteorological Satellite Studies,University of Wisconsin-Madison)和SARTA(Stand-Alone Radiative Transfer Algorithm)辐射传输模式模拟的亮温辐射值。归纳总结了2种通道信息的提取及降维方法:一是采用有效的方法来完成光谱信息压缩,对常用的主成分分析和独立分量分析方法进行了对比,认为独立分量分析更为可行。二是通道选择,即保留部分含有较多大气廓线信息量的通道,达到降维目的。在进行通道选择时要注意针对不同地区气候类型、下垫面、季节以及即时天气条件,选择不同的通道组合。介绍了3种反演算法:特征向量统计法、牛顿非线性迭代法和神经网络法。对比发现特征向量统计法简单易行,但精度不够理想;牛顿非线性迭代法精度虽高但计算耗时长,因此不适合业务使用;神经网络计算速度快、精度也能达到要求,具有很好的前景。对目前的几种样本分类方法及附加因子进行了对比分析,对反演算法精度的改进提出了一些有益的设想。最后对晴空辐射订正及云天大气水汽廓线反演进行了简要介绍,提出了该领域未来的一些研究方向。
Satellite microwave thermal emissions mixed with signals from active sensors are referred to as radio- frequency interference （RFI）. Based on Advanced Micro- wave Scanning Radiometer-Earth Observing System （AMSR-E） observations from June 1 to 16, 2011, RFI over Europe was identified and analyzed using the modified principal component analysis algorithm in this paper. The X band AMSR-E measurements in England and Italy are mostly affected by the stable, persistent, active microwave transmitters on the surface, while the RFI source of other European countries is the interference of the reflected geostationary TV satellite downlink signals to the measurements of spacebome microwave radiometers. The locations and intensities of the RFI induced by the geostationary TV and communication satellites changed with time within the observed period. The observations of spacebome microwave radiometers in ascending portions of orbits are usually interfered with over European land, while no RFI was detected in descending passes. The RFI locations and intensities from the reflection of downlink radiation are highly dependent upon the relative geometry between the geostationary satellite and the measuring passive sensor. Only these fields of view of a spaceborne instrument whose scan azimuths are close to the azimuth relative to the geostationary satellite are likely to be affected by RFI.
利用2009年不同季节COSMIC湿反演的大气温度和相对湿度廓线数据,分别与时、空相匹配的ECMWF(European Centre for Medium-Range Weather Forecasts,欧洲中尺度天气预报中心)、NCEP(National Centers for Environmental Prediction,美国环境预报中心)模式客观分析场和无线电探空观测数据,进行全球范围的比较分析。初步研究表明,无论夏季还是冬季,各种资料源之间相互比较的偏差和标准差分布相似,与季节无关。就温度而言,三种资料源的温度水平、垂直分布都很接近,ECMWF模式数据比NCEP不论是温度廓线还是湿度廓线都更接近COSMIC反演值。模式的水汽客观分析场在对流层基本上都比无线电探空观测值偏湿,对流层中高层在大部分海洋地区也比COSMIC反演场偏湿。COSMIC反演的相对湿度相对于无线电探空整层偏大,具有明显正偏差,在300 h Pa偏差达最大值(约30%)。
