CRYOSAT-2 SAR Mode Closed to the Coast: Processing Methods, Data Quality Assessment and Benefits
Boy, François1; Picot, Nicolas1; Desjonqueres, Jean-Damien1; Moreau, Thomas2; Labroue, Sylvie2; Thibaut, Pierre1

In the frame of the Sentinel3 project, CNES is involved in the overall topography payload product quality. Sentinel3 embarks an altimeter including a conventional LRM mode and a SAR mode. The SAR mode propose enhanced performances compared to the conventional mode, thanks to a reduced along track resolution (from 10km to 300m) and a lower mesurements noise level. However, while there is a long experience of LRM data processing, SAR nadir looking data are new and will need extensive prototype development and an in depth validation. To contribute to those analysis, CNES took the opportunity of the availabilty of CRYOSAT-2 SAR data over ocean and started, two years ago, the development of a Cryosat processing Protoype to generate Level2 product including Sea Level Anomaly and Significant WaveHeigh information from both LRM L1B and SAR FBR products.

At 2012 OSTST and AGU, Boy et al presented the SAR processing strategy and the first results over deep ocean. But beginning 2013, CNES has modified its processing prototype in order to implement a processing method suitable for the coastal areas. Indeed, SAR data are very promising approaching the coast since the reduced along track resolution will allow to go closer to the coast (less land contamination into the altimeter waveform) and providing finer measurements thanks to the lower noise level. In the frame of the ESA Living planet, we will adress this topic, presenting how we have optimized the CNES SAR processing methods for this particular areas. Indeed, some signal processing technics that are extensively used for SAR Imaging missions as Over Sampling and Hamming can now be used in altimetry. We will compare the pro and cons of these technics over different types of surfaces and situations. Results will be compared to results from LRM classical measurements as JASON-2. Moreover, we will report the results of independant data quality assessment performed by coastal expert PIs who accepted to analyse precisely several months of SAR data processed by the CNES processing prototype. In particular a focus on the Mediterranean sea will be presented.