The study proposed in this paper deals with the analysis, in the time-frequency domain, of a L-band signal reflected by an time-evolving sea surface. The final goal of this project is to evaluate the technical potential of passive GNSS based systems to estimate oceanographic parameters. With this purpose in mind, this paper presents the experimental setup and describes the physical modeling applied to generate numerical simulations. We put more particular stress on the time-frequency representation of the signal received by an observer above the time-evolving sea surface. Finally, physical interpretations of the features obtained in the time-frequency domain from these simulated signals are proposed.