Model of near-space limb contrast based on non-local thermodynamics equilibrium model

A physical model was established for studying near-space limb radiance contrast when the target is detected by space-borne infrared surveillance system. The definition of limb contrast and radiation issues of upper atmosphere of the model was described in detail. The target' s limb contrasts were simulated and analyzed to show upper atmospheric radiation properties' effects to the target visibility based on non-local thermodynamics equilibrium atmospheric model and assumed detector' s noise. The results indicate that the detector' s noise must be considered for evaluating surveillance feasibility correctly. The contrast at the traditional waveband of the strong absorption by water vapor is better than the often-used atmospheric windows' for the upper atmospheric limb detection. The complicated contrast characteristics result from the relationship among target inherent radiation, atmospheric absorption and background radiation.