A study of the electromagnetic bias for GNSS-R ocean altimetry using the choppy wave model

Abstract

Global Navigation Satellite System-Reflectometry (GNSS-R) altimetry involves measuring reflections of Global Positioning System transmissions from the Earth’s surface (a bistatic radar configuration.) These reflected signals carry information about the Earth’s surface, including the sea surface height. The electromagnetic (EM) bias is a significant error source when measuring sea surface height with GNSS-R due to the non-symmetric properties of sea waves. Although previous studies of the EM bias have been conducted for traditional backscatter altimetry, information on the EM bias in the bistatic configurations important for GNSS-R is limited. Of particular interest is the influence of the bistatic geometry on the EM bias. This paper presents a study of the EM bias in GNSS-R altimetry. The study employs a Monte Carlo procedure with numerical nonlinear hydrodynamic simulations coupled with a physical optics method for EM scattering from the sea surface to produce a deterministic set of sea surface profiles and the corresponding GNSS-R waveforms. In this initial study, “choppy wave” model is used for nonlinear surface description in order to improve further the computational efficiency and one-dimension surface analysis is chosen for the simple computations. The influence of the bistatic configuration on the EM bias properties has analyzed, and it is shown that the EM bias varies approximately as a cosine function of the incident angle and that “short wave” effects make important contributions.