Absolute spectroradiometric calibration of the ADS40 sensor

Digital cameras have spectral and radiometric properties superior to analogue film cameras. Due to its radiometrically stable construction the ADS40 sensor is capable of making images for cartography as well as remote sensing applications. For the increased size of current projects, for sensor fusion, as well as for change detection purposes it is necessary to produce comparable images for different flight conditions (weather, camera system, etc.). This is not possible with classical film cameras since comparable images require the absolute radiometric calibration of the imaging system, before atmospheric correction, reflectance calibration and BRDF correction can take place. The methods for satellite laboratory calibration can be also used for digital airborne cameras. A laboratory calibration of the ADS40 is made with a calibrated integrating sphere in order to determine dark signal, lens falloff, and radiometric gain for each sensor line. For the ADS40 a linear radiometric model is sufficiently accurate. The knowledge of the system spectral response allows a more accurate calculation of the radiometric calibration coefficients and is a check for system integrity. In order to provide a regional camera service, radiometric calibration facilities are being established on several service sites of the world.