Numerical simulation of the radar signal modulation due to the long ocean waves: preparation of the VAGSAT mission

VAGSAT has been proposed in 1993 in response to an announcement of opportunity from the French Space Agency for a small-satellite mission. It has then been selected as one of the possible candidates for a future satellite mission. The aim of this project is to measure at the global scale the directional spectra of the ocean surface waves (in the [70-500] m range of wavelengths). The proposed system is a K_u-band radar (frequency ≈13.4 GHz) using real aperture antenna. The originality of the concept of VAGSAT is to propose an alternative to synthetic aperture radar systems (imaging radars) which present important limitations over the ocean because of the nonlinear character of the imaging process. The authors present the characteristics of VAGSAT and the principle of the measurement. The developments carried out to simulate the radar data and the statistical uncertainties associated with the retrieved wave directional spectra are also presented