GNSS Ocean Bistatic Statistical Scattering in the Time-Varying Regime: Modeling and Correlation Properties

The main contributions to signal decorrelation in Global Navigation Satellite Systems Reflectometry (GNSS-R) over the ocean are known to be the platforms motion and the sea surface roughness. These two actions play at different timescales: of the order of few milliseconds, the former and hundreds of milliseconds, the latter. Currently, bistatic scattering models as well as simulators do not provide a rationale for sea surface correlation, whose nature is essentially random. In this work, the scattered signal is modeled as the sum of incoherent contributions arising from single spatial regions that correspond to delay-Doppler cells in the glistening zone. The statistical model of the signal scattered by a moving sea surface is derived by introducing a process for appearing and disappearing of local scattering cores on the sea surface. The scatterers lifetime is governed by a birth-death-immigration process; in the limit of a large number of scatterers, a compound Gaussian process arises, whose temporal statistics are investigated. The analysis of the signal correlation and of the correlation time is considered for the case of an airborne receiver.