Stereoscopic mapping with thermal infrared images

Thermal infrared cameras using an imaging array, do have similar geometric conditions like perspective photos. So a geo-reference of the determined object temperatures is possible by means of orthophotos. A sufficient geometric accuracy requires the knowledge of the image geometry which is not available by the factory. A first test of the used ThermScan camera by self calibration with bundle block adjustment of a flight over a dump, failed because of problems with the exact image tie. The tie points in thermal infrared images cannot be measured with the same pixel accuracy like in corresponding photos based on the visible spectrum The gray values are based on differences of the object temperature which is usually limited and edges are not so well defined. By this reason a laboratory calibration with a test field, marked by small bulbs, was made. Depending upon the used optics, radial symmetric distortions of 1 pixel and not symmetric distortions of 1.5 pixels have been determined. Based on the geometric calibration, a block adjustment is possible. This is the required geometric information for a stereoscopic mapping and the creation of orthophotos with thermal infrared images.