A simulation method of 3D cirrus radiance images for space-based missile warning detectors

High-altitude cirrus clouds are main clutter sources for space-based missile warning in 2.7μm band, their radiance images can serve as an important guide in designing and evaluating early warning systems. First of all, the 3D finite element model of atmosphere (include clouds) was constructed, and its corresponding discrete radiative transfer calculation method was derived as well. Then, the geometry and scattering properties of cirrus were given for the special application in 2.7μm band. With the auxiliary calculation of MODTRAN, the primary and secondary factors in the radiative transfer process were distinguished leading to a simplified radiance calculation means. Finally, a new method was proposed to generate radiance images by integrating source functions in the chief ray pathway of each camera pixel. The simulated results were given and compared with the results of SHDOMPP (Spherical Harmonic Discrete Ordinate Method for Plane-Parallel Atmospheric Radiative Transfer) program, which prove the correct projecting relationship between the 3D cirrus sense and its image on detector focal plane, and validate the rationality and credibility of the proposed method in quantitative radiance calculation.