2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/86210In this paper we focus on the microwave bistatic scattering process, with the aim of deriving an expression for the interferometric complex field auto-correlation function from a static platform. We start from the Fresnel integral and derive the auto-correlation function in the Fraunhofer and Modified Fraunhofer regime. The autocorrelation function at short times can be expressed as a Gaussian with a direction dependent time scale. The directional modulation is a function of the angle between the scattering direction and the wave direction. The obtained relation can be used for directional sea state estimation using one or more GNSS-R coastal receivers.Starlab Preprint 18062004-01. V2 corrected a typo, V3 adds a clarification on the definition of Modified Fraunhofer approximationAtmospheric and Oceanic PhysicsInstrumentation and Detectorstext