Retrieval of wet snow by means of multitemporal SAR data
Retrieval of wet snow by means of multitemporal SAR data
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DOI：
10.1109/36.842004
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发表时间：
2000-03
期刊：
影响因子：
--
通讯作者：
T. Nagler;H. Rott
中科院分区：
文献类型：
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作者：
T. Nagler;H. Rott
提出了一种利用重复通过合成孔径雷达（SAR）图像绘制山区湿雪的算法。作为算法开发的基础，利用ERS合成孔径雷达数据和奥地利阿尔卑斯山试验场的实地测量，对无雪和有雪覆盖的阿尔卑斯山表面的后向散射特性进行了研究。来自SAR数据的后向散射的入射角的依赖性进行了比较与模拟无雪的表面和表面覆盖的干雪和湿雪。后向散射的季节变化显著，这主要是由雪中液态水含量和表面粗糙度的变化引起的。表面粗糙度的重要性后向散射湿雪的表面粗糙度实验证明。用于映射湿雪的算法使用湿雪与无雪或干雪表面的比率来应用变化检测。主要步骤包括配准、斑点减少、比率图像的阈值化、地理编码，以及可选地，交叉通道的组合以减少由于停留造成的信息损失。据认为，雷达卫星和欧洲遥感合成孔径雷达将湿雪与其他表面分开的阈值为-3分贝是适当的。基于历史雪图或地形信息的后处理步骤用于校正高海拔地区的干雪区域。通过比较具有19/spl deg/视角的ERS SAR图像和具有40/spl deg/视角的Radarsat SAR波束模式S7图像，研究成像几何结构的影响。合成孔径雷达和大地卫星5号专题成像仪图像的雪图比较表明，在封闭的积雪覆盖区，雪图吻合较好，而雪线/合成孔径雷达附近往往略低估积雪范围。
An algorithm has been developed for mapping wet snow in mountainous terrain using repeat pass synthetic aperture radar (SAR) images. As a basis for algorithm development, backscattering properties of snow-free and snow-covered alpine surfaces were investigated using ERS SAR data and field measurements at test sites in the Austrian Alps. The incidence angle dependence of backscattering derived from SAR data is compared with simulations for snow-free surfaces and for surfaces covered by dry snow and wet snow. Significant seasonal changes of backscattering are observed, which are mainly caused by variations of the snow liquid water content and of the surface roughness. The importance of surface roughness for backscattering of wet snow is demonstrated by a surface roughness experiment. The algorithm for mapping wet snow applies change detection using ratios of wet snow versus snow-free or dry snow surfaces. The main steps include coregistration, speckle reduction, thresholding of ratio images, geocoding, and, optionally, combination of crossing passes to reduce the loss of information due to layover. A threshold of -3 dB was found to be appropriate for both Radarsat and ERS SAR to separate wet snow from other surfaces. Postprocessing steps, based on historic snow maps or topographic information, are used to correct for dry snow areas at high elevations. Effects of imaging geometry are investigated by comparing ERS SAR images with a look angle of 19/spl deg/ and Radarsat SAR Beam Mode S7 images with a look angle of 40/spl deg/. The comparison of snow maps from SAR and Landsat-5 Thematic Mapper images shows good agreement in areas of closed snow cover, whereas near the snow line/SAR tends to slightly underestimate the snow extent.