Infrared Radiation Model For Aircraft And Reentry Vehicle

NIR.ATAM ( NATO InfraRed Air T.Arget Model ) is a computer model which predicts IR radiation of an aircraft in its natural surroundings. A special version of NIRATAM enables to treat a hypersonic reentry vehicle. The model takes into account the IR radiation emitted by aerodynamically and internally heated surface, hot engine parts and combustion gas and particles in the exhaust plume. The reflected radiation of the sky and terrain background and the sun on the aircraft surface is calculated. The atmospheric transmission and emission between target and observer and the radiation of a homogenous background in the scene is determined. The spectral response of a sensor is included. The development took place in collaboration with other NATO-countries. The code is of modular structure. One of the major modules (IRMA) , for the hot gas emission calculation, was developed at This paper describes the modules, the major features and shows some typical results. For the "Reentry-Version" the exhaust plume flew field model is replaced by an aerodynamic flow field model which determines the hypersonic flow around the body. A thermal model computes the aerodynamic heating and heat balance of the body by considering the convection , the thermal conduction and the radiative heat loss. A dynamic thermal map of the surface is computed for the course of reentry. The principal model components and steps for &terming the IR-signature are discussed and results for a typical reentry vehicle are presented in the paper. The code is applicable in the spectral range from 2 to 25 μm with 5cm ' spectral resolution. Radiation of gas can be predicted within the temperature range from 100 -- 3000° K . The results are presented as emission spectra and their cumulated integrals. Thermal images are provided in radiance and equivalent blackbody temperature values. The contributions of the different radiation sources are analysed.