Sea state observation using ground-based GNSS-SNR data

The signal-to-noise ratio (SNR) data is widely used in GNSS reflectometry to derive water or snow surface heights and surface characteristics like roughness or soil moisture. In a marine environment the attenuation of the SNR oscillation is related to the roughness of the sea surface. It was shown that the significant wave height (SWH) of the water surface can be calculated from the analysis of the attenuation.

The attenuation depends strongly on the relation between the coherent and the incoherent part of the scattered power. The correlation length of the sea surface governs the incoherent part and varies with respect to the direction of the line of sight relative to the wave direction. The resulting anisotropic characteristic of the attenuation yields a directional pattern of the cutoff angle at which the coherence is lost. The cutoff angle can be deduced from the attenuation of the SNR data, from which the wave direction can be derived. The contribution will recapitulate the relation between the sea state and the cutoff angle based on sea surface simulations and present the analysis of experimental data from a GNSS station in the North Sea.

A sea state observation would be incomplete without an information about the wave period. The wave period does not influence the SWH but the correlation length of the sea surface. Hence, for a particular SWH, different peak wave periods should yield different correlation length for a line of sight in the wave direction. Analysis based on sea surface simulations show that it should be possible to derive the peak wave period as a function of the SWH and the maximum cutoff angle of the SNR attenuation. The results of this analysis will be presented here, too.