1. Department of Geodesy and Geoinformation, TU Wien, 1040 Vienna, Austria
2. Earth Observation Data Centre for Water Resources Monitoring (EODC), 1030 Vienna, Austria
3. V.O.F. APSS, 4725 SJ Wouwse Plantage, The Netherlands
4. Department of Geography, University of Zurich, CH-8057 Zurich, Switzerland