NLTE-based atmospheric radiance modeling for space-based 4.3μm infrared detection of rocket exhaust flames

The radiance characteristics of the atmosphere background provide the basis for rocket exhaust flame detection and tracking. The traditional atmospheric radiance model uses the LTE (local thermodynamic equilibrium) model. However, at high altitudes (above 50 km), the number density distribution of molecular is no longer a function of thermodynamic temperature, at which point the molecules are in NLTE (non-local thermodynamic equilibrium). Aiming at the requirement of space-based infrared detection of the rocket exhaust flame, a modeling method of space-based background radiance characteristics was established based on the coupling of remote sensing data and the NLTE model. Further, considering the background radiance characteristics of the cloud background in the detection view of the geosynchronous orbit infrared detection system, the radiance contrast of the rocket exhaust flame in the infrared band of 4.3μm are discussed, and the detectability of the narrow band within 4.3μm is analyzed. The results show that the NLTE effect has a significant effect on the radiance and transmittance of the atmosphere, and will reduce the contrast of the infrared radiance of the rocket exhaust flame. In the modeling process of space-based detection of background radiance, it is necessary to consider the influence of the NLTE effect in the middle and upper atmosphere. This paper provides support for infrared detection of rocket exhaust flame targets.