As part of the absolute calibration process, the SDSU IP Lab has developed the capability to estimate the optical properties of the atmosphere at the time of satellite overpass. These estimates are based on openly available meteorological data and satellite data, or actual ground measurement data obtained by the lab, that are used as inputs to the Modtran radiative transfer function software. The outputs from this modeling are a gain and bias coefficient that are used in a linear equation to remove atmospheric effects. The customer receives either atmospherically corrected imagery or else the bias and gain parameters that are subtracted from and divided into the imagery to perform an atmospheric correction. The resulting product for the customer is an image where the values of the pixels are upwelling radiance at the surface or, more commonly, surface reflectance. An example of the input and output data produced from this work is shown in Figure 6.
Figure 6a and 6b show an example of input and output for Atmospheric Correction. Figure 6a is a plot of atmospheric aerosol values at a single location obtained from several satellite sensors using databases that are publicly available on the internet. Aerosol is one atmospheric parameter that is used as an input variable for atmospheric modeling. Figure 6b shows the results of atmospheric correction for a Landsat image of Brookings, SD. The left hand image is quite blue due to excessive atmospheric scattering at this wavelength. The right hand image is obtained after atmospheric correction using the optimized SDSU model that removes the atmospheric effects and allows a surface based look at vegetation. As a result, the blue haze is removed, and the vegetation now is the normal green color. The image in the center is the result of a non-optimized model available in the radiative transfer code.