三江源地区卫星被动微波遥感特性的初步分析

Prilimary Analysis on Polarimetric Microwave Radiation in Sanjiangyuan Region

微波可以穿透云层,可以全天候监测目标区域,还可以比较有效地分辨水体、植被、冰雪和荒漠等。因此,微波遥感资料是研究地表类型众多的三江源地区的有效手段。全球第一个星载全极化微波辐射计WindSat测量的第3和第4个Stokes参数T3和T4,作为前所未有被卫星传感器大面积、长时间序列测量的亮温,为三江源地表目标的探测研究提供了新的工具和方法。仅使用垂直和水平极化亮温TV和TH,会将小面积水体和沼泽误识别成荒漠。结合WindSat辐射计所测量的4个Stokes参数,可以较好地分辨三江源地区的典型目标,例如雪山、湖泊和荒漠等,有利于消除由于地表目标识别错误导致的土壤湿度研究可能存在的潜在误差。TV,TV-TH,MPDI(MPDI=(TV-TH)/(TV+TH))以及T3等值线的走向基本体现出西南东北走向,这与该区域植被分布自东南向西北为针叶林、高山草甸草原、干旱草原及荒漠的特点密切相关。冰雪融化和凝结,以及植被的生长和消亡,使得该区域微波辐射的季节性变化显著。前视和后视垂直极化亮温TV及T3的差值表明,该区域的微波辐射随观测方位角的变化是,雪山积雪冰川和湖区的辐射方向性较强,而植被和荒漠的辐射方向性较弱。

With its cloud-penetrating capability, the microwave radiometer can provide all-weather information of ground surface, except for rainy areas. WindSat, the first polarimetric microwave radiometer in the world, can measure all of the four Stokes parameters. The third and fourth Stokes parameters, which have never been measured globally and for a long time, can be used to study Sanjiangyuan region. The types of ground, such as water, vegetation, hungriness and so on, can be easily distinquished according to all of the four Stokes parameters. Small lakes and swamps may be mistaken as bare soil or hungriness by using only vertical and horizontal polarimetric brightness temperature TV and TH. So, the identification with four parameters can eliminate errors with respect to soil moisture. In this respect, the microwave radiometer is superior in studying Sanjiangyuan, where there are various types of ground. The trends of isolines of TV, TV-TH, MPDI （MPDI=（TV-TH）/（TV＋TH）） and the third Stokes parameters T3 are generally southwest-northeast for forest of conifer, plain of meadow, droughty plain, hungriness distributed from southeast to northwest. The microwave radiation changes seasonally along with melting and freezing of ice and snow, growing and decaying of vegetation. The differences between TV and T3 of forward looking and back looking show that the microwave radiation of Sanjiangyuan region is anisotropic. The anisotropy of snow and ice and lake is stronger than that of vegetation and hungriness.