Shi Li-Juan, Qiu Yu-Bao, Shi Jian-Cheng
Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100094, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2013 May;33(5):1157-62.
The microwave emissivity is a function of structure, water content, and surface roughness, and all these factors have obvious seasonal variations. In the present study, the half-month averaged emissivities in summer and winter of 2003 over the vegetation of Northern Hemisphere were estimated using Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) combined with IGBP (International Geosphere-Biosphere Project labels) land classification data. Then the emissivities of vegetation land covers at different frequencies, the polarization and their seasonal variations were analyzed respectively. The results show that the emissivities of vegetation increase with the increase in frequencies, and decline with the frequency increasing over snow region. In summer, the vegetation emissivity at V-polarization of 89 GHz is larger than 0.944, and all emissivities are relatively stable and the RMSE of time series emissivity variation is less than 0.007 2. In winter, emissivities decrease over snow covered area, especially for higher frequencies. Furthermore, with the increase in vegetation density, the emissivities increase and emissivity polarization difference decreases.
微波发射率是结构、含水量和表面粗糙度的函数，并且所有这些因素都有明显的季节变化。在本研究中，利用先进微波扫描辐射计-地球观测系统（AMSR-E）结合国际地圈-生物圈计划（IGBP）土地分类数据，估算了2003年北半球植被在夏季和冬季的半月平均发射率。然后分别分析了不同频率、极化情况下植被覆盖地的发射率及其季节变化。结果表明，植被的发射率随频率增加而增大，而在雪区则随频率增加而减小。夏季，89GHz垂直极化的植被发射率大于0.944，且所有发射率相对稳定，发射率时间序列变化的均方根误差小于0.0072。冬季，在积雪覆盖区域发射率降低，尤其是高频情况。此外，随着植被密度增加，发射率增大，发射率极化差异减小。
