Satellite altimeters, designed to measure the topography of the ocean, are also good imagers of the ocean surface backscatter. A method was developed to invert the classical Low Resolution Mode high resolution HR waveforms in terms of surface backscatter at high resolution (similar to 300m). Since the launch of Cryosat-2 in 2010, a new generation of altimeters using Doppler capabilities has emerged and has become the standard for the new altimeters such as the Sentinel-3 one. The so-called SAR altimetry provides higher along-track resolution and lower noise level. In this mode altimeter are also good imagers of the surface backscatter. A new method of inversion of SAR waveforms is presented. The processing of the Sentinel-3 altimeters provides collocated SAR and LRM waveforms that are used to intercompare the inverted surfce backscatter.