A Numerical Study on the Influence of Ocean Surfacewaves on Gps-reflected Signals

1. ABSTRACT The ability to investigate properties of the sea surface by means of navigation signals has recently received growing interest from the remote sensing community. This innovative technique is known as Global Navigation Satellite System-Reflectometry (GNSS-R), and it relies on signals of opportunity transmitted from GNSS Constellations (e.g. GPS, Glonass, Galileo etc.), and reflected from the surface of the ocean, to look at a variety of ocean properties, primarily ocean surface roughness (scatterom-etry), but also sea surface height (altimetry). The retrieval of ocean roughness from GNSS-R data has now been demonstrated with a reasonable level of accuracy both from airborne [1] and spaceborne platforms [2]. GNSS-R signals are available globally, all the time and over the long term, and could potentially provide high-density global measurements of sea surface roughness, that are relevant for operational uses and scientific purposes, as well as to support climate Earth Observation missions such as SMOS. Having shown in [2] that it is possible to retrieve the Directional Mean Square Slope of ocean height (DMSS) from UK-DMC Satellite Delay-Doppler Maps (DDMs) using the established theoretical scattering model by Zavorotny & Voronovich [3] (the Z-V model hereafter), we now focus on the implementation of an end-to-end simulator of the scattering of GPS signals from realistic sea surfaces. This approach was mainly motivated by the differences highlighted in [2] between the measured DDM and the DDM simulated using the Z-V theoretical model [3]. The Z-V model is sufficiently advanced to retrieve directional roughness information from GNSS-R data with reasonable accuracy, but it relies on a high-frequency limit approximation, the Geometric Optics (GO) for the scattering, and is able to describe the average sea surface scattering only. Our end-to-end simulation approach aims to address these limitations through the use of explicit realizations of the sea surface from which the scattering is computed, and through a more general scattering model, which accounts for the scattering from both large-scale and small-scale roughness components. Moreover, the vector formulation of the scattering here, as opposed to the scalar formulation used in [3], allows us to explore the effect of polarization, the importance of which has already been recognised and stressed from observations and modeling efforts as in [4] and [5]. In this work, the simulation of wind waves on the ocean surfaces is carried out by filtering a white Gaussian noise with the theoretical wave spectrum model described in [6], dependent only …