Optical EngineeringFast Risley prisms camera steering system: calibration and image distortions correction through the use of a three-dimensional refraction model
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To improve airborne search and rescue operations and the general aerial surveillance efficiency, new concepts of multiple field-of-view and variable-resolution imagers have been developed. These imagers provide surveillance operators with simultaneous wide area coverage and high-resolution imaging. Over the last years, several optical steering systems have been developed and field tested in operational conditions. These developments helped us to develop a novel camera steering system using achromatic Risley prisms. This simple and sturdy steering system allowed us to move rapidly and precisely the field of view of an infrared camera. To improve its performance, a three-dimensional (3D) refraction model was applied to enable fast pointing direction calibration and correction of distorted images. Image deformations were analyzed, and a fast linear image correction based on homographic transformation and the 3D refraction model are presented. Experimental results of mosaicking applications with real imaging systems in the 3- to 5-μm, 8- to 12-μm infrared, and 850- to 860-nm visible bands demonstrate the improvements achieved with the homographic image distortions correction and the fast pointing calibration procedure.