Attenuation correction of airborne gamma-ray spectrometric data using digital terrrain models. Gamma-rays are partially absorbed in air on there way from Earth's surface to the sensor package in the aircraft, thus attenuated following an exponential law, coming from a footprint area with a few hundred metres diameter. This effect shall be removed as far as flying height deviates from some nominal flying height. Instead of assuming a flat surface, this is done for the true travel distance of the gamma-rays using digital terrain models and an arbitrarily fine sector system around the sensor package.