Synthetic Aperture Radar (SAR) Altimetry for Hydrology
Martin-Puig, Cristina1; Amador, Javier2; Martinez-Val, Bernat1
1isardSAT, SPAIN; 2Universidad de Oviedo, SPAIN
Over the last decade Climate Change has been of growing concern; such is that the Global Climate Observing System (GCOS) in support to the United Nations framework convention on climate change (UNFCCC) and the intergovernmental Panel on Climate Change (IPCC) has defined a set of Essential Climate Variables (ECVs) to allow for its quantification. This paper offers an innovative solution for the monitoring of one terrestrial ECV: lakes level by the use of Synthetic Aperture Radar (SAR) altimetry mode data.
Lakes level inferred from conventional altimetry [Ref. 1][Ref. 2] has shown promising results in the last decade. However, one of the main constrains of this technique for this purpose relies on its along-track resolution. The application of SAR techniques to classical radar altimetry may offer a potential solution to significantly enhance Earth surface mapping, thus provide better estimates of currently observed lakes or even allow for the identification of small water bodies not distinguishable with current missions. The key innovation of this new altimetric mode is the addition of along-track processing for increased resolution and multi-looking. In turn, this allows for accumulation of more statistical independent looks for each reduced scatting area under observation, leading to better Speckle reduction, hence finer precision of altimetric measurements. With the ''recent'' launch (Spring 2010) of Cryosat-2 this satellite is the first of its kind allowing for scientific users to investigate for specific regions in the globe the expected theoretical potentialities of this new altimetric mode in preparation for the future missions Sentinel-3 and Jason-CS also with a SAR altimeter on board.
This paper focuses on investigating the potentialities of this new altimetric mode for hydrology. Precisely, our work will focus on investigating the Chinese Qinghai-Tibet plateau lakes since these represent the main source of fresh water for Chinese population. To this aim CryoSat-2 SARM L1b products will be retracked with isardSATīs SARM L2 retracker inherited from the SAMOSA contract [Ref. 3], which has been adapted at isardSAT for lakes and rivers monitoring. Results will be validated and cross-calibrated with in situ and other altimetric missions. Performance indexes and overall achievements will be presented. Furthermore, we will also aim at providing suggestions and recommendations for forthcoming missions with a SAR altimeter to be applied for lakes monitoring.
[Ref. 1] Aladin, N.V., Crétaux, J-F., Plotnikov, I.S., et al. Modern hydro- biological state of the Small Aral Sea. Environmetric 16, 1-18, doi:10.1002/env.709, 2005.
[Ref. 2] Crétaux, J-F., Kouraev, A. V., Papa, F., Bergé Nguyen, M., Cazenave, A., Aladin, N.V., Plotnikov, I.S. Water balance of the Big Aral Sea from satellite remote sensing and in situ observations. J. Great Lakes Res. 31 (4), 520534, 2005.
[Ref. 3] Surface Topography Mission (STM) SRAL/MWR L2 Algorithms Definition, Accuracy and Specification. ESA doc ref S3PAD-RS-CLS-SD03-00017. June 2011.