Computing Specular Points Over Complex Land Surfaces for Airborne GNSS-R Applications.

This paper proposes a novel global-to-local (G2L) searching algorithm to find the locations of specular reflections over terrestrial surfaces for GNSS-R applications. In the proposed method, an initial coordinate of the specular reflection is first computed on a smooth WGS84 datum using the Fibonacci method. Second, a local coordinate frame that is centered at the initial WGS84 specular point (SP) is defined with respect to the local topography, and the G2L searching algorithm is applied to more precisely locate the specular reflection point. The effects of the complex land topography, including the local slope and incidence angles, are considered. This method is simulated for an airborne GNSS-R scenario where the receiver position is based on historical flight data from Gisborne to Wellington in New Zealand, where the results show that the finalized SP positions have been significantly shifted due to the complex topographical surfaces. This G2L method can be implemented to accurately track the location of reflected GNSS signal power from measured delay-Doppler maps (DDM) for land applications.