CryoSat-2 SARin Mode for Coastal Altimetry
García-Arnaud, Pablo1; Martin-Puig, Cristina1; García-Mondéjar, Albert1; Roca, Mònica2
1isardSAT, SPAIN; 2isardSAT, POLAND

The CryoSat-2 (CS-2) mission is an altimetric mission designed to meet the measurement requirements for ice-sheet elevation and sea-ice 'freeboard'. Its main payload is a Synthetic aperture Interferometric Radar ALtimeter (SIRAL) operating in three different modes: Low Resolution Mode (LRM, equivalent to pulse-limited mode), Synthetic Aperture Radar Mode (SARM) and SAR interferometric mode (SARin). CryoSat-2 is the first of its kind since it has on board a SARM/SARin altimeter for the first time. In addition to Cryospheric applications, this mission is of great interest to the Hydrosphere and Oceanographic communities since it allows for quantitative assessment of expected enhanced altimetric capabilities in coastal monitoring, ocean floor topography, gravity field and inland water monitoring.

Under the framework of the CryoSat Plus for Ocean (CP4O) project (ESA/ESRIN STSE funded) isardSAT has the responsibility to investigate the potentialities of exploiting SARin mode for coastal altimetry applications. This paper aims at presenting isardSAT main achievements within CP4O, as well as further investigations done at isardSAT for the exploitation of the mode to enhance sea level mapping at coastal regions.

When operating in SARin mode the altimeter measures the phase difference of the backscattered echoes at the two receiving antennas. This information allows for the derivation of the Angle of Arrival (AoA), and so the reflection points at any range bin can be geolocated.

In coastal altimetry land contamination highly degrades the backscattered echo. This is sometimes, but not always, overcome with the SARM when tracks are perpendicular to the coast, since this mode provides a resolution enhancement with respect to LRM mode along-track [Ref. 1]. However, across-track interferences still remain an issue in coastal altimetry and our expectation is that SARin mode may provide a solution for their cancellation.

This paper is aiming at investigating CS-2 Level-2 (L2) SARin retracked results and determining if they are coherent with the AoA information in line with our activities at the CP4O project. In addition, we will apply isardSAT SARM L2 retracker inherited from the SAMOSA contract [Ref. 2] adapted to SARin, and analyze if there are any improvements with respect current SARin data retracker by the CS-2 ground processor to this aim. The methodology of our work will be based on investigating lose of track and mitigation of coastal contaminations with the usage of phase information from the SARin mode. A new CS-2 SARin area covering the Cuban archipelago has been created to meet this CP4O investigation needs.

[Ref. 1] S. Dinardo, B. Lucas and J. Benveniste. SAR Altimetry in coastal zone: performances, limits, perspectives. Oral presented at the 5th Coastal Altimetry Worshop, San Diego, CA, USA, 2011.

[Ref. 2] Various. Surface Topography Mission (STM) SRAL/MWR L2 Algorithms Definition, Accuracy and Specification. ESA doc ref S3PAD-RS-CLS-SD03-00017. June 2011.