River discharge monitoring using Earth Observation techniques is a major challenge for hydrologists for the water resources management as well as the surveillance of climate changes. In northern regions, for instance, rivers are heavily impacted by climate changes. The melting of permafrost raises the income of water in river and consequently flooding and land erosion caused by the increase of river discharge. Water current measurement is a main variable for the calculation of river discharge. These researches aim at estimating this water surface current using radar Along Track Interferometry (ATI) techniques. The Along Track Interferometry technique is based on the comparison of the phase of two SAR images acquired with two antennas separated with a short distance in the along-track direction. The two images are acquired with the same geometrical configuration separated by a short time lag. The phase difference between the two images comes from the short time lag between the two acquisitions and the movement of the target (water particles) during this time lag. Therefore, the target radial velocity, toward or away from the radar, is estimated from this phase difference. Images have been acquired on the Rhone river (France) with the RAMSES SAR sensor (ONERA) operating at X band. The ATI techniques applied to the images acquired during the campaign allowed the extraction of a surface velocity map. The analysis of this map shows that the ATI techniques are very promising and are consistent with ground measurements acquired simultaneously (using ADCP) to the radar acquisition. Surface current profile, across the river section, extracted from the map matches the current profile extracted from ADCP measurements. A radar backscattering model using a specific water surface roughness model is under investigation. The roughness model is based on the study of the movements of water particles in wind induced short waves and the velocity of these waves on water surface under different wind stress conditions. The comparison between simulated data using this radar backscattering model and real data will allow the development of a reverse model of the radar signal to estimate water surface current and thereby the accuracy of water current measurement using EO techniques.