短波红外垂直失水指数对大气效应的敏感性分析

Analysis of Sensitivity of Shortwave Infrared Perpendicular Water Stress Index to Atmospheric Effect

在业务应用中,用光学遥感方法反演地表土壤水分时常常会因受到大气效应的影响而降低精度。利用中分辨率成像光谱仪(Moderate Resolution Imaging Spectroradiometer.MODIS)的卫星观测数据、相应的地表反射率产品以及辐射传输模型模拟方法,评估了短波红外垂直失水指数(Shortwave Infrared Perpendicular Water Stress Index,SPSI)对大气效应的敏感性。结果表明,大气效应会使近红外和短波红外波段的反射率呈线性增加,但对由近红外和短波红外波段组成的光谱特征空间中的典型三角形分布以及像元间几何关系影响较小,能够在一定程度上补偿大气效应对土壤水分反演的影响。因此,在实际的区域化应用中,可以不考虑大气效应给SPSI指数计算及土壤水分反演带来的不确定性,从而简化业务流程。

In practical applications, the accuracy of optical remote sensing data is often reduced because of the influence of atmospheric effect. The sensitivity of Shortwave Infrared Perpendicular Water Stress Index （SPSI） to atmospheric effect is evaluated by using the data from the Moderate Resolution Imaging Spectroradiometer （MODIS）, the corresponding ground reflectivity product and the atmospheric transfer model simulation. The result shows that the atmospheric effect can make the reflectivity in near infrared and shortwave infrared bands increase linearly. However, since it has less influence on the typical triangular distribution and the geometric relationship among the pixels in near infrared and shortwave infrared spectral space, the influence of atmospheric effect on soil moisture inversion can be compensated to a certain extent. Therefore, the uncertainty brought by atmospheric effect to SPSI and relative soil moisture can be ignored in practical applications and the operational process can be simplified.