Coherent GPS Reflections Over Ocean Surface

This paper presents assessment on the coherency of reflected GPS signals received on a LEO satellite for high accuracy ocean altimetry applications. We analyze the coherent signal levels dependence on sea surface conditions and signal parameters based on GPS reflection data collected by Spire cubeSats between January and April 2019. The data contains carrier phase estimations obtained from an open-loop tracking process sampled at 50Hz for GPS carrier frequency L1 and L2. A conservative coherency quality test based on two circular statistics of the carrier phase measurements, circular-length and circular-kurtosis, is applied to the data. The results show that ~ 1% and ~40% of the events contain sufficient coherent energy for high precision altimetry applications over ocean and sea ice respectively.