Theory and Implementation of an End-to-End Radio Occultation Simulator

Rapport, 2014

In this report we present the results of a project aimed at developing an end-to-end radio occultation simulator. The project was a cooperation between Chalmers University of Technology, RUAG Space AB, and OHB Sweden, and financed by the Swedish Space Board within the second National Space Research Program (NRFP-2). The simulator includes a wave optics propagator (WOP) capable of simulating realistic GNSS signals as they propagate through the Earth’s atmosphere using realistic refractivity, a routine for propagating the signal to LEO, a routine for adding noise to the received signal, and a routine for interpreting the signals in the terms of bending angle and impact height (in our case achieved using phase matching). In this report we go through the theory behind each of these techniques, we describe how to implement them in Matlab, and we evaluate the accuracy of each step. In addition to this, and in order to evaluate the results from the code, it was necessary to make a detailed investigation into geometrical optics (GO) and the Abel transform. Mainly to find a fast and accurate way to calculate the results from geometrical optics, but as a spin-off we also present a small investigation into the problem with Abel inversion for super-refractive refractivity profiles.