Validation of CryoSat-2 SAR and SARin modes over rivers for the SHAPE project

Nicolas Bercher (Along-Track, France)


Pierre Fabry (Along-Track, France); Américo Ambrózio (DEIMOS/ESRIN, Italy); Marco Restano (SERCO/ESRIN, Italy); Jérôme Benveniste (ESA-ESRIN, Italy)

Event: 2016 SAR Altimetry Workshop

Session: SAR mode performances: SAR CALVAL from Cryosat-2 and Sentinel-3

Presentation type: Type Poster

In the frame of the preparation of Sentinel-3A SAR altimeter satellite, this study addresses the processing and validation of water levels derived from CryoSat-2 data over rivers. This work is part of the SHAPE project, the SEOM Sentinel-3 for Science Inland Waters activity. Meanwhile real Sentinel-3A data are available, the project focuses onto the use of CryoSat-2 data and try to mimic them as much as possible.

Previous studies have highlighted the benefits of the CryoSat-2 mission for the monitoring of river water levels. The on-board SIRAL altimeter implements altimetric SAR mode for the first time (as well as SARin mode), together with conventional low resolution mode (LRM). However, compared to conventional satellite altimetry missions, CryoSat-2 flies on an unusual geodetic orbit characterised by a long orbit period (369 days) and a dense spatial coverage (7km at equator).

This unusual orbit, for hydrology, induces an unusual sampling of the rivers path and make the water level measurements spread in space, along the river path, and in time. This exciting and challenging feature requires to develop and implement data processing in new and specific ways. One objective being to cancel the spatial component of the water level variations in order to retrieve the usual sampling pattern in which data are spread in time only (and thus are local time series).

One major topic developed in this work is what we call the migration of CryoSat-2 measurements along the river path. The migration is used to derive pseudo time series at given arbitrary places. It involves a group of local CryoSat-2 measurements in which we try to cancel the local spatial variations, according to an estimated longitudinal river profile.

The presentation of this work is broke down into three parts, with an emphasis on performing the validation of drifting/geodetic orbit data. There are:

(1) the estimation of longitudinal river profile from third party altimetry missions flying over the same river,

(2) the migration of the CryoSat-2 measurements along the river path to built local "pseudo time series" (i.e., in which local spatial variations were removed),

(3) the estimation of the errors that are attributable to the migration process itself, based in in situ data only.

In the end, validation results in SAR, and SARin mode for reference, against in situ data will be presented. The tools are implemented in the case of the Amazon river for which sufficient in situ data and gauging stations allow to perform the 3 points mentioned above.

Poster show times:

RoomStart DateEnd Date
Grande Halle Mon, Oct 31 2016,18:30 Mon, Oct 31 2016,19:30
Nicolas Bercher