摘要
用辐射传输理论提出的地表微波辐射极化指数PI的定义 ,分别指出了土壤湿度、地面粗糙、植被层和大气层的各自影响。用DMSPSSM/I多时相 6年的数据给出中国主要陆地 19.35GHz通道的PI值月平均分布 ,表征土壤湿度的月变化 ,并获得中国主要陆地同季同月PI距平值ΔnPI的统计分布 ,展示了中国陆地土壤湿度变化的分布图 ,以及在干旱与水涝期间PI距平值的异常 ,用中国山西 2 0 0 1年 5月的干旱和中国长江中游 1998年 8月水涝作了个例证明。这一理论方法可同样推广到有较低频率 (如 10 .7GHz)的 2 0 0 2年 5月发射的AMSR E或中国风云系列卫星微波成像辐射计的通道 ,而获得土壤湿度分布更好的PI指数评估。在已知区域平均PI值与平均土壤湿度的条件下 ,可以定量反演该区域的土壤湿度 。
Denoting the polarization difference, a polarization index (PI) of microwave radiance from the terrain surface is derived from the radiative transfer model. This PI separates the radiance effects of the soil surface moisture, surface roughness, vegetation canopy and atmosphere, and can be focused on mapping the land surface moisture. As example, statistics of the monthly average from multi-temporal 6 years data of the DMSP SSM/I observations at lowest 19.35 GHz channel is obtained to individually demonstrate variation of the land surface moisture. The deviation of the PI data at the same month from the , i.e. ΔnPI(≡(PI-)/), gives prominence to focusing surface moisture variation and its anomaly shows possible drought or flood occurrence. The ΔnPI mapping is validated by the examples of the drought in China's Shanxi area in May 2001 and the flood around China's Yangtze River in August 1998, respectively. The approach is recommended to lower frequency channels to minimize the influence from vegetation canopy for future application (such as 10.7 GHz of the AMSR-E launched in May 2002 and microwave imaging radiometer of China's Fengyun satellite series). When the monthly and the ground truth of average volumetric moisture v> of the region are available, it is tractable to retrieve the land surface moisture by using the PI data at the same month and the same region without much knowledge of surface roughness, vegetation canopy and others. As an example, the retrieval of v> is favorably tested by using the TRMM TMI data.
出处
《电波科学学报》
EI
CSCD
2004年第4期386-392,共7页
Chinese Journal of Radio Science
基金
国家重点基础研究规划项目 (2 0 0 1CB30 94 0 1)
国家自然科学基金资助项目(6 0 1710 0 9)
