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).

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As methods continue to develop for predicting infrared signatures for complex propulsion systems, the need to validate such methods and, indeed to gain confidence in new designs grows. Within Dstl, work to develop static engine test rigs has been carried out. These rigs allow aspects of infrared signature such as plume mixing, cavity emissions, surface impingement and subsequent treatment, obscuration and nozzle shaping to be studied. However, there is a growing need for data, which is more closely related to actual flight conditions. Full flight measurements are prohibitively expensive and often out of the question when a range of geometries are to be studied. Wind tunnel tests can also be difficult because of the quantity of power required for the free stream flow and the need to produce realistic hot gas. This paper describes the work that has been carried out to produce a cost effective free stream measurement capability, which makes use of existing static engine facilities. By bleeding engine compressor flows and exhaust flows, a reduced scale system has been created which allows the simulation of infrared propulsion issues at free stream Mach numbers of up to 0.5. The data obtained with this system has been used to validate the prediction methods for 3D-exhaust plume and afterbody infrared signature.