Passive Ranging Using a Dispersive Spectrometer and Optical Filters
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
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Monocular passive ranging using atmospheric oxygen absorption has been demonstrated in the past using an FTS. These instruments are very sensitive to vibration making them di cult to use on an airborne platform. This work focuses on whether passive ranging can be done with instruments that are easier to deploy. Two potential instruments are tested and compared a diffraction grating spectrometer and optical filters. A grating spectrometer was able to estimate range to within 5 for a static solid rocket motor ring at a distance of 910 m using the NIR absorption band of oxygen. Testing at shorter ranges produced range estimates accurate to within 5 for the NIR band and 15 for the visible band. Using the sun as a source, optical filters were able to successfully measure the pathlength through the atmosphere to within 3 for both bands. Testing the filters using a quartz lamp as the source, however, proved unsucessful. A system is discussed and modeled in ZEMAX to potentially measure multiple filters simultaneously. A model was also created to predict how both techniques will scale to longer ranges. Using filters is predicted to be more accurate at long ranges, but only if the grating spectrometer has to be ber coupled to the collection optic.