Illumination compensation in LANDSAT-images to improve land-use classification in the German Alpes

In order to enable accurate land-use classifications in mountainous areas atmospheric influences and solar illumination changes with slope and aspect have to be allowed for. A method was developed for compensating these effects and it is demonstrated on a part of a LANDSAT-TM-Scene of a region in the German Alps. A fine-resolution digital elevation model (DEM) is necessary to perform an illumination correction. In order to adapt the geometry of the DEM and the TM-image, the relief displacement of each pixel of the TM-image was calculated and corrected. The DEM was used to calculate the total shortwave solar irradiance at the time of overflight. As the ratio of the diffuse and direct fraction of the irradiance changes with the wavelength the calculated irradiance was modified for each TM-band using a LOWTRAN-based procedure. The comparison of the classification results of the uncorrected and corrected image show an increase of the classification accuracy from 62% without illumination compensation to 77% with illumination compensation