<title>Modeling multispectral imagery data with NIRATAM v3.1 and NPLUME v1.6</title>

Abstract

Spectral imagery data(2.0 to 5.4 ¡rm) was collecred of plumes of ships by the NATO Special Working Group 4 (ttl).tr provides the means to study the signature of a target spectrally, spatially, and temporally. This experimental data hai been used to validate the infrared signature of the plume of a ship as computed by NATO's flow-field program NpLUME vl.6 and the NATO Infra-Red Air Target Model NIRATAM v3. t. Two spatial positions in the spectral imagery data cube were selected. One which represents the background specçum, and one which represents the spectrum of the plume of the ship. Theoretical spectra were computed by means of NpLUME vl.6 and NIRATAM v3.1. A computed background spectrum was fitted to the experimental bãckground spectrum using a userdefined atmosphere in accordance with the meteorological conditions during the trial. A cõmputed plume spectrum was fitted to the observed plume spectrum in order to determine the chemical composition of the exhaust gãs. Since NIRATAM onþ takes into account plume radiation from CO, CO2, HrO, and soot, the analysis is necessarily limite¿ to these species. Using the derived fitting parameters from the experimental data we make predictions about the infrared signature of the plume in two wavelength bands (mid-wave infrared and the long-wave infrared). The average transmission through the plume in the mid-wave infrared (3.0 to 5.0 ¡rm) ranges from 65 o/o close to the exit plane, io 100 % where the plume dissolves in the ambient atmosphere. For the long-wave infrared (8.0 to 10.0 ¡rm) the range in transmission is 90 % to 100 %o. The active species in the mid-wave infrared and the long-wave infrared are the same foi the plume as for the intervening atmosphere' The main difference is that the absorption features are deeper and wider for the plume. Based on this work we arrive at the conclusion that spectral imagery data of the plume of a ship can be adequately modeled using NIRATAM v3'l in conjunction with NPLUME vI.6. Alternatively, the experimenral d;ta validates NIRATAM v3.l and NPLUME vI.6. Some modifications to the NIRATAM source code have been proposed as a result of this study. A new release of NIRATAM and NPLUME which incorporates some of these changes is expetted shortly (NIRATAM v3.2).

Infrared signature studies of aerospace vehicles

“…The code also predicts the effect of carbon particles on IR emission characteristics of plume. Bakker et al [73] gave a brief methodology for computing plume IR signatures from naval ship gas turbine engines, using NATO's NPLUME program for exhaust field computations.…”