Atmospheric correction including the BRDF influence of the target

The atmospheric correction program ACUMAM (atmospheric correction using MODTRAN and more) considers the influence of the bi-directional reflectance distribution function (BRDF) for the corresponding surface target and is based on a semi-analytic solution of the radiative transfer equation. The key of the method is a special separation of the directly transmitted surface radiance from the total measured one. It takes advantage of the statistical BRDF features derived from a number of BRDF models and field measurements. The path scattered radiance of the atmosphere and the various atmospheric transmission functions which are used in ACUMAM do not depend on the actual BRDF of the surface. They are calculated from the output radiances of MODTRAN and from the results of the radiative transfer code which was written by Diner and Martonchik, 1984. Their code works for Lambertian as well as non-Lambertian surface BRDFs. The presented atmospheric correction program can be adapted to any passive remote sensing sensor which operates in the solar spectral range. In order to evaluate the accuracy of ACUMAM it was tested with simulated radiances and real air and space borne measurements. The simulation procedure was restricted to the technical parameters of the wide angle optical spectral sensor (WAOSS). This sensor has the capability to perform multi-angular measurements in the near infrared spectral region. It will be mounted on the bi-spectral infrared detection (BIRD) micro-satellite which will fly next year.