The depth of absorption bands in observed spectra of distant, bright sources can be used to estimate range to the source. Experimental results are presented based on observations of the O<sub>2</sub> X(v? = 0) ? b(v? = 0) absorption band centered around 762 nm and the O<sub>2</sub> X(v? = 0) ? b(v? = 1) band around 689 nm. Range is estimated by comparing observed values of band-average absorption against predicted curves derived from either historical data or model predictions. Accuracy of better than 0.5% was verified in short-range (up to 3 km), static experiments using a high-resolution (1 cm<sup>-1</sup>) spectroradiometer. This method was also tested against the exhaust plume of a Falcon 9 rocket launched from Cape Canaveral, Florida. The rocket was launched from an initial range of 13 km and tracked for 90 s after ignition. Range error was below 2% for the first 30 s and consistent with predicted error throughout the track.
Michael R. Hawks, R. Anthony Vincent, Jacob Martin, and Glen P. Perram, "Short-Range Demonstrations of Monocular Passive Ranging Using O2 (X3Σg- → b1Σg+) Absorption Spectra," Appl. Spectrosc. 67, 513-519 (2013)