Potential of SARAL/AltiKa for Inland Water Applications

Abstract

SARAL uses the same orbit as ERS and Envisat and can be used to extend inland water height time series derived from these missions. This article investigates the potential of SARAL for this application over the Great Lakes and the Amazon basin. SARAL/AltiKa is the first altimeter using Ka-band that is rarely influenced by ionospheric effects but susceptible for atmospheric water. Our investigations show clear waveform disruptions for SARAL due to precipitation. It is demonstrated that the quality of water heights improved when using alternative retracker products, for example, the ice-1 product. The improvement depends on the weather and yields up to 3.8 cm for wet conditions. The advantage of the smaller footprint of SARAL is demonstrated for land-water transitions where SARAL provides better water level heights up to 6 km to the lakeshore whereas Envisat is limited to about 11 km. SARAL provides also more reliable water level heights for narrow Amazon rivers than Envisat. Furthermore, the hooking effect is decreased for SARAL. Comparing water level time series of SARAL-only, Envisat-only, and multi-mission with in-situ data demonstrates that SARAL has the potential to extend Envisat long-term time series and to decrease the RMS by about 10% for large lakes and 40% for selected rivers.

Keywords:

• SARAL/AltiKa
• Envisat
• inland water 

Acknowledgements

The used altimeter data are based on altimetry missions operated by CNES/NASA (TOPEX, Jason-1), ESA (Envisat), CNES/NASA/Eumetsat/NOAA (Jason-2), and ISRO/CNES (SARAL). The SGDR data sets are disseminated by AVISO, ESA, NOAA, and PODAAC. We thank the National Oceanic and Atmospheric Administration (NOAA) and the Agência Nacional de Águas (ANA) for providing water levels of gauges for validation. We also thank the Great Lakes Environmental Research Laboratory (GLERL) for providing data about ice coverage of the Great Lakes.

Funding

This work was funded by the Deutsche Forschungsgemeinschaft (DFG), Bonn, Germany, under the grants, BO1228/6-3. This work was also supported by Deutsche Forschungsgemeinschaft (DFG), Bonn, Germany, through the TUM International Graduate School of Science and Engineering (IGSSE).