The Optical Design Of VIS/IR Dual-band Airborne Reconnaissance Systems

There is a growing need for dual band cameras in airborne reconnaissance systems having simultaneous multi-band measurement recently. Performance about 0.1m of ground resolvable distance (GRD) at 20000m altitude has been realized in the UAV abroad. The dual band requirement stems from considerations of system performance and cost as well as installation on the platform.There are three optical system structures as reflective systems, refractive systems and catadioptric systems. Based on the information of domestic and overseas literatures, this article reports a new dual band airborne camera, within sphere platforms about 480mm in diameter, designed for simultaneous registration of both visible and IR imagery. The camera design uses a common front end Cassegrain optical system and several relay optical sub-systems capable of delivering both high spatial resolution visible and IR images to the detectors. To enable the operation of the dual band, a unique dichroic beam splitter with special coating and broad band anti-reflection coating is required. The visible optical path is designed dual field-of-view with 0.5m/1m focal length, relative aperture of 1:4/1:8,1''/3 with 1024×766pixels of detector format and pixel size of 4.7μm , obtaining GRD of 0.188m/0.094m at 20000m altitude and the MWIR optical portion designed with fixed focal length of 0.5m, relative aperture of 1:4,with 640×480 IR cool FPA of 15μm pixel size reaching GRD of 0.6m. Three fundamental issues have been analyzed, of which the result indicates this system within 350mm×280mm(diam×h) provides high-resolution images in the thermal IR at night and simultaneous IR and visible images during day, completely meeting the requirement of the airborne reconnaissance platforms currently.