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Performance penalties associated with infrared (IR)-signature suppression (IRSS), e.g., increased engine back pressure, weight, drag, cost, and complexity, can shift the engine operating point to higher combustion temperatures. Extra weight degrades aircraft flight performance in terms of reduced range, higher length needed for takeoff, reduced maneuverability, etc. Lift-induced drag penalty due to increased weight shifts the aircraft gas turbine engine operating point to a higher combustion temperature. But the divergent section of the convergent-divergent (C-D) nozzle gives the extra thrust up to optimal flow expansion, which more than compensates the increased lift-induced drag corresponding to its weight. Thus, for the same thrust, an engine with a C-D nozzle operates at a lower combustion temperature than with a convergent nozzle.

This paper outlines a quick method of estimating the transmissivity of the intervening atmosphere (between the infrared detector and the object to be detected - aircraft/missile), for vertical and slant beams of infrared radiation. The data needed is the transmissivity for horizontal beams of infrared radiation, of a given length, at various altitudes. The intervening atmosphere is discretized into regions of constant extinction co-efficients and the transmissivities of these regions are multiplied together to find the transmissivity of the intervening atmosphere.