被动微波遥感雪深反演中积雪特性与下垫面的散射与辐射机理研究

The underlying boundary is the key factor of snow cover identification in the derivation of snow depth from passive microwave remote sensing. The temperature of frozen soil induces to the misclassification of snow cover, but has not been considered, although some research have been performed on the influences of soil moisture and roughness on emissivity. Snow characteristics, especially snow grain size, is the main factor influencing the retrieval accuracy of snow depth, but the observation and parameterization scheme of it are influenced by manual observation, resulting in large uncertainty of snow depth estimation. This study will implement an experiment in the Altay in Xinjiang province to obtain the brightness temperature and back scattering coefficients of K and Ka bands, several parameters related to grain size using different measurement methods, analyze the relationship between these parameters and scattering coefficients and backscattering coefficients, and finally find out a stable parameterization scheme of grain size. The brightness temperature and backscattering coefficients of ground with different temperature at K and Ka bands will observed at the Altay and Binggou watershed, as well as other soil parameters, to build the relationship between the temperature of underlying soil and emissivities at K and Ka bands. And the results from the research on grain size and ground temperature are finally applied apply in the snow depth derivation over the Qinghai-Tibetan plateau to improve the accuracy of it.

在被动微波雪深反演中，下垫面边界条件是积雪识别的关键，虽然已有研究针对土壤发射率受土壤水分和粗糙度的影响，但目前并没有考虑冻土温度引起的积雪误判问题。积雪特性，尤其是积雪粒径是影响雪深反演精度的主要因素，但是其观测和参数化受人为因素的影响较大，具有较大的不确定性。本研究在新疆阿勒泰开展积雪观测实验，获取K和Ka波段的微波亮度温度和后向散射系数，利用不同方法观测雪粒径参数和其他积雪特性信息，分析不同雪粒径参数、后向散射系数与不同频率微波散射系数的关系，探寻稳定的粒径参数化方案。在阿勒泰和祁连山冰沟流域开展不同土壤温度条件下K和Ka波段的微波辐射计和散射计以及土壤参数观测，分析土壤温度对不同微波频率的亮度温度影响机制，建立土壤温度与不同频率亮度温度的关系。将土壤温度和雪粒径研究结果应用于青藏高原的雪深反演中，提高雪深或雪水当量反演精度。

被动微波遥感是目前全球和区域尺度上最有效的雪深反演方法。但在被动微波雪深反演中，下垫面边界条件是积雪识别的关键，虽然已有研究针对土壤发射率受土壤水分和粗糙度的影响，但没有考虑冻土温度引起的积雪误判问题。积雪特性，尤其是积雪粒径是影响雪深反演精度的主要因素，粒径变化给反演带来了较大的不确定性。本研究在新疆阿勒泰开展积雪地基微波辐射计和积雪特性观测实验，获取逐日积雪特性，以及K和Ka波段的微波亮度温度，开展积雪微波辐射传输模型模拟工作，分析积雪特性演化对微波亮度温度的影响，发展了K和Ka波段积雪体散射模型。并将散射模型替换多层积雪微波辐射传输模型MEMLS中已有的体散射模型，提高模型模拟精度。考虑到青藏高原土壤温度对不同微波亮度温度的影响，以及被动微波空间分辨率粗，无法描述以瞬时积雪为主要特征的青藏高原积雪分布状态，本研究分析了土壤温度对不同微波频率的亮度温度影响机制，结合光学遥感反演的地表温度、积雪面积以及微波亮度温度，获取了青藏高原不同频率发射率的空间分布。在MEMLS模型中考虑不同的地表发射率，发展被动微波雪深反演算法，并结合光学遥感反演的500m积雪面积比例以及积雪衰减曲线发展青藏高原500m雪深反演算法。