An Inverse Problem in Astronomy: Earth Occultation Transform Imaging

Dr. Shuang-Nan Zhang

Universities Space Research Association and
Marshall Space Flight Center

February 13, 1998

Abstract

The fluxes of gamma-ray sources in the sky detected by the BATSE detectors aboard the NASA CGRO satellite are periodically modulated by the Earth occultation. The modulation can be described in close analogy to Radon Transform, which is the integral of a two dimensional function along a straight line. Thus the gamma-ray sky can fully reconstructed by applying the Radon Theorem, if sufficient Earth occultation sampling of the sky is available. However, the limited sampling in practice makes the inverse problem ill-posed. We have applied the Maximum Entropy principle to achieve the first continuous all-sky imaging of the gamma-ray. Recently another yet more complicated ill-posed inverse problem has been recognized for another NASA satellite to be launched soon. Solving this problem would also enhance the scientific capability of this mission significantly.