Recent development in the 3-12 µm radiometric calibration of the DAIS 7915

Kurzfassung

Radiometric calibration of sensors in the thermal infrared region is a critical issue especially for the DAIS 7915. As the scan mechanism of the DAIS is of the Kennedy type, there is a considerable fraction of intrinsic background radiation in the overall signal presented to the detector. The contribution of the background to the total signal increases towards larger scan angles. Until 1998 the 6 Bands in the 8-12 µm region were calibrated using the two external blackbodies of the DAIS operated at different temperatures during airborne data takes. This method did not account for scan angle dependencies other than the theoretical Kennedy intrinsic vignetting. Evaluation of in-flight data made evident that this is method is not satisfactory. The mid infrared band was not calibrated at all due to uncertainties in the estimation of emitted and reflected radiation components of the blackbody and housing. A new approach was therefore developed using a simplified sensor model. This paper presents the calibration strategy, which is based on laboratory measurements. The thermal data are processed and calibrated using laboratory coefficients, blackbody readings and scanner housing temperature measurements. This paper introduces the technique, the algorithm and its implementation. Examples of laboratory and in-flight data are shown together with results of a preliminary in-flight validation.