CoAuthors

Eduard Makhoul (isardSAT UK, United Kingdom); M. Joana Fernandes (University of Porto, Portugal); Mònica Roca (isardSAT Barcelona, Spain); David Cotton (Satellite Oceanography Consultants, UK); Marco Restano (Serco/ESRIN, Italy); Jérôme Benveniste (ESA/ESRIN, Italy)

The advent of SAR altimetry has prompted a radical rethinking of the amount of information contained in the altimetric echoes, and has brought along advanced processing techniques that exploit the Doppler information in the signal. Many groups around the world are at work to refine aspects of the processing with the aim of an improved (i.e. more accurate) retrieval of the traditional parameters (height, wave height, normalized backscatter and mis-pointing) or even new parameters such as the mean square slope. A review of the state of the art in SAR altimetry has been carried out recently within the ESA SCOOP project; this contribution summarises the results of that review and describes the key progress points on which research is focusing, and the remaining challenges still faced by SAR altimetry. Recent improvements have been both in the L1A to L1B processing and in L1B to L2: they include the weighting of the SAR stack and the exploitation of the power distribution in the stack for new observables, the retracking of individual Doppler beams, the computation on a finer ground step, the fully focused SAR processing, the compensation of amplitude variations and look dilation in the stack, some improvements in the L2 retracking models and specific approaches to the retracking in the coastal zone. Those are accompanied by improvements in the range corrections required to account both for the path delay induced by the water vapour in the altimeter signal (Wet Tropospheric Correction) and for the sea state effects, with active research being carried out at present to derive a SAR mode Sea State Bias solution and to compensate for expected effects of swell on the SAR footprint.