SATELLITE ATMOS. CORRECTION COEF. (FIFE)

The atmospheric effects on the transmitted and reflected solar radiation should be factored into the estimation of geophysical and biophysical parameters from remotely-sensed data, so that appropriate correction schemes can be employed to infer reflectivity of the ground from satellite radiometric data. Some of the correction techniques require derived coefficients as inputs in the algorithms that perform the atmospheric correction. As part of the FIFE staff science data collection effort, the FIFE Information System (FIS) utilized atmospheric correction and related algorithms to generate coefficients for deriving corrected values from the FIFE level-1 image products. These coefficients were used by FIFE staff in calculating site reflectances from pixel values extracted from the level-1 imagery. The Fraser (Fraser et al., 1992) and LOWTRAN 7 (Kneizys et al., 1988) models were used for computation of coefficients used to correct radiances of scattered radiation measured by aircraft and/or satellite during FIFE. The Fraser algorithm is designed to compute the surface reflectance for a given measured radiance, or alternatively, the upward radiance at an arbitrary height when the surface reflectance is given. LOWTRAN 7 is a low-resolution propagation model and computer code for predicting atmospheric transmittance and background radiance from 0 to 50,000 [cm^-1] at a resolution of 20 [cm^-1].在利用遥感数据（remotely-sensed data）估算地球物理与生物物理参数的过程中，必须考虑大气对传输及反射太阳辐射产生的影响，以便通过合适的校正方案，从卫星辐射数据中反演地表反射率。部分大气校正（atmospheric correction）算法需要将衍生系数作为输入参数。作为FIFE科研数据采集工作的一部分，FIFE信息系统（FIFE Information System, FIS）借助大气校正及相关算法，从FIFE一级影像产品（level-1 image products）中生成用于获取校正后数值的系数。FIFE科研人员利用这些系数，从一级影像提取的像素值中计算各站点的反射率。在FIFE项目期间，针对航空器和/或卫星测得的散射辐射亮度（radiance）的校正系数计算，采用了Fraser模型（Fraser等，1992）与LOWTRAN 7模型（Kneizys等，1988）。Fraser算法可针对给定的实测辐射亮度计算地表反射率；反之，若已知地表反射率，也可计算任意高度处的上行辐射亮度。LOWTRAN 7是一款低分辨率传输模型及计算机代码，可用于预测0至50000 [cm⁻¹]波段范围内、分辨率为20 [cm⁻¹]的大气透过率与背景辐射亮度。