Passive ranging of dynamic rocket plumes using infrared and visible oxygen attenuation

Abstract

Atmospheric oxygen absorption bands in observed spectra of boost phase missiles can be used to accurately estimate range from sensor to target. One method is to compare observed values of band averaged absorption to radiative transfer models. This is most effective using bands where there is a single absorbing species. This work compares spectral attenuation of two oxygen absorption bands in the near-infrared (NIR) and visible (Vis) spectrum, centered at 762 nm and 690 nm, to passively determine range. Spectra were observed from a static test of a full-scale solid rocket motor at a 900 m range. The NIR O 2 band provided range estimates accurate to within 3 %, while the Vis O 2 band had a range error of 15 %. A Falcon 9 rocket launch at an initial range of 13 km was also tracked and observed for 90 seconds after ignition. The NIR O 2 band provided in-flight range estimates accurate to within 2 % error for the first 30 seconds of tracked observation. The Vis O 2 band also provided accurate range estimates with an error of approximately 4 %. Rocket plumes are expected to be significantly brighter at longer wavelengths, but absorption in the NIR band is nearly ten times stronger than the Vis band, causing saturation at shorter path lengths. An atmospheric band is considered saturated when all the in-band frequencies emitted from the rocket plume are absorbed before reaching the sensor.

Monocular passive ranging through a PQ:PMMA holographic wavelength division demultiplexer

“…More specifically, MPR as first proposed by M. R. Hawks 1 observes the optical spectrum of an emissive target around the 762 nm absorption band of O2 as well as the non-absorbing 750 nm and 780 nm bands in order to calculate the total transmissivity of this particle species, from which a range estimate can be obtained. This method has been used to estimate distance for rockets, fighter jets, and reference lamp sources [2][3][4][5][6] , yielding errors below 7% and 3% for long and short distance experiments, respectively. However, most of these experiments have been performed either with a Fourier transform spectrometer or by switching between three bandpass filters in series, significantly impacting the feasibility of the systems.…”

Monocular Vision Ranging and Camera Focal Length Calibration

“…Monocular vision-based ranging methods can be divided into three categories, including proportion-based methods, machine learning-based methods, and coordinate transformation-based methods. Proportion-based methods are according to the principle that the distance is inversely proportional to the image's size from the target in the image plane [4,5]. Taking the ranging model proposed by Bao and Wang [5], this model first assumes the width of all vehicles as a fixed value and then uses this value to learn the model parameters from the images of vehicles at different distances.…”

Short-Range Demonstrations of Monocular Passive Ranging Using O2 (X3Σg− → b1Σ+g) Absorption Spectra

“…The spectral resolution was typically chosen as 4 cm −1 , although experiments show the results are largely independent of instrument resolution. 9,-10 The instrument field of view (FOV) was 4.9 mrad, although smaller field stops were sometimes used to limit the background light. A video camera boresighted to the instrument was used to ensure the source was not clipped by the field stop.…”