Radiometric calibrations of sensor data are routinely performed using one or more radiation sources at different radiance levels. Calibration of spectral bands in the thermal infrared region (> 2.0 µm) is needed due to the bias drift which is a characteristic of the detector technology (e.g. MCT, InSb). To maintain the accuracy during an extended measurement the calibration has to be frequently repeated. The complexity of the radiometric calibration increases even more when a) the number of spectral bands to calibrate increases, b) the spectral range of the sensors to calibrate increases, c) the radiation level of the scene or object under interest (like hot spots) increases. If the accuracy in the calibration is to be maintained, all these factors will both increase the time needed to perform the calibration and the number and/or complexity of the radiation sources needed. Either or both may be impractical to handle during a field trial. In this paper we have studied the radiometric calibration of spectral bands in the mid wave infrared region (MWIR, 1.5 - 5.5 µm), with the focus on hot spots. The model and methodology proposed are however general and can be applied on an arbitrary set of sensor data collected in the 0.4 - 12 µm spectral region. Data was obtained from a cooled multi-band sensor based on an MCT detector. The study also includes the development of a SWIR source practical for field trials.