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Navigation, especially in aviation, has been plagued since its inception with the hazards ofpoor visibility conditions. Vehicular ground movement is also hampered at night or in low visibility even with night vision augmentation because of the lack of contrast and depth perception. For landing aircraft in fog, the visible and near-infrared have been discounted because of the large backscatter coefficients in favor of primarily radar that penetrates waterladen atmospheres. Aircraft outfitted with an Instrumentation Landing System (ILS) can land safely on an aircraft carrier in fog. Landing at an airport with an ILS is not safe because there is no way to detect small-scale obstacles that do not show up on radar but can cause a landing crash. We have developed and tested a technique to improve navigation through fog based on chopped active visible laser illumination and wide baseline stereo (hyperstereo) viewing with real-time image correction of backscatter radiation and forward scattering blur. The basis of the approach to developing this active hyperstereo vision system for landing aircraft in fog is outlined in the invention disclosure ofthe Army Research Laboratory (ARL) patent application ARL-97-72, filed Dec. 1997. Testing this concept required a matched pair of laser illuminators and cameras with synchronized choppers, a computer for near real-time acquisition and analysis of the hyperstereo imagery with ancillary stereo display goggles, a set of specular reflectors, and a fog generator/characterizer. The basic concept of active hyperstereo vision is to compare the imagery obtained from alternate wings ofthe aircraft while illuminating only from the opposite wing. This produces images with a backscatter radiation pattern that has an increasing gradient towards the side with the illumination source. Flipping the imagery from one wing left to right and comparing it to the opposite wing imagery will allow the backscattered radiation pattern to be subtracted from both sets of imagery. Use of specular reflectors along the sides of the runway will allow the human stereo fusion process to fuse the forward scatter blurred hyperstereo imagery of the array of specular reflectors with backscatter eliminated and allow the appropriate amount of inverse point spread function deblurring to be applied for optimum resolution of scene content (i.e., obstacles on the runway). Results of this testing will be shown.
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