Modeling of Diffuse Photometric Signatures of Satellites for Space Object Identification.

Abstract : The diffuse reflective characteristics of four types of low earth orbit satellites were mathematically modeled using phase functions for ideal Lambertian surfaces. A FORTRAN computer program was developed to generate simulated signatures and compare them point by point to real signatures to obtain a sum of the squares of the residuals (SSR), in order to perform pattern recognition and satellite identification. One set of signatures was used to validate the computer model of one satellite type, and the others were used to test the program's ability to identify the satellite. The tested model involved line-of-sight obcuration of some parts by others, relative motion of body parts, and for phase shadowing. The program was able to correctly identify the modeled satellite, as long as the phase angle remained small, generally less than ninety degrees. For larger phase angles, the true signatures diverged significantly from simulated signatures. In every case, the signatures predicted using the Lambertian assumption were dimmer than the measured signatures at larger phase angles.