APPLICATION OF SYNTHETIC APERTURE RADAR METHODS FOR MORPHOLOGICAL ANALYSIS OF THE SALAR DE UYUNI DISTAL FLUVIAL SYSTEM A. M. Oyen, R. Koenders, S. E. Hosseini Aria, and R. C. Lindenbergh Dept. of Geoscience and Remote Sensing Delft University of Technology J. Li and M. E. Donselaar Dept. of Geoscience and Engineering Delft University of Technology ABSTRACT Knowledge of the present-day activity of river channels in dis- tal fluvial systems strongly contributes to the reconstruction of past branching and avulsion processes. Established remote sensing techniques can be applied to monitor the formation of flooding planes (crevasse splays) and channel activity. In this research variations in the amplitude in Synthetic Aperture Radar images are interpreted as soil moisture changes. Inter- ferometric SAR showed minor phase changes during dry sea- son and loss of coherence after peak run-off. After peak dis- charge during the dry season in 2009 reactivation of multiple avulsed river paths and crevasse channels was detected. These results show that analysis of SAR images can contribute to the monitoring of fluvial systems. It is expected that these initial results will be confirmed by field data and analysis of alterna- tive remote sensing data sources. Index Terms— SAR, InSAR, channel morphology, en- dorheic basin, Salar de Uyuni 1. INTRODUCTION Distal fluvial systems in a low-gradient, semi-arid, endorheic setting are poorly understood currently. In particular, the ori- gin of the branching river channel morphology at the river terminus is a hot topic of debate: Is it the result of a distribu- tary pattern of simultaneously active channels or is the mor- phology the result of one or many river channels [1, 2, 3]? In order to answer this question a reconstruction of the de- positional history of a fluvial system should be made, which considers: (1) the avulsion history, and (2) the development of crevasse splays and terminal lobes. Mapping of previous and present-day active channels, crevasse splays, and termi- nal lobes will aid the reconstruction of the depositional his- tory. In addition, the correlation between the areal extent of crevasse splays and channel width and depth provides infor- mation about the downstream changes in crevasse sheet size and intensity. Crevasse splays originate during peak run-off when the channels are not able to contain the stream and mas- sive flood-out brings water and sediment onto the floodplain which borders the river. This work shows the application of Synthetic Aperture Radar (SAR) remote sensing for studying the distal fluvial system south of Uyuni city in the Bolivian Altiplano Basin. The main goal is to map changes after rainy seasons and sin- gle rainfall events. Two SAR analysis techniques with each their own application are used: amplitude analysis (changes of soil characteristics) and interferometry (deformation). The main challenges of this particular application of SAR remote sensing are the spatial resolution of the data and its availabil- ity. Furthermore, the high precipitation rates during rain sea- son as well as large single rainfall events in the dry season decrease the correlation between certain image pairs. There- fore, the image pairs should be selected carefully. 2. REGION OF INTEREST The Salar de Uyuni is the world’s largest salt lake, located in the Bolivian Altiplano Basin at an altitude of 3653 m. Ge- ological markers indicate that the present lake water level is much lower than in history. This results in a very flat land- scape near the present lake margin. These low slopes shape the terminal parts of the feeding rivers which are characterised by many branching channels with decreasing depth and width towards the terminal lobes. The Bolivia Altiplano Basin ex- periences heavy rain seasons and very dry summers. The precipitation during peak run-off cannot be contained in the river channels resulting in reactivation of old channels, chan- nel cut-offs and flooding events creating so-called crevasse splays. The chronology of the branching of these channels and their activity is the key question in this field. This work focusses on the Colorado river system to the South-East of Salar de Uyuni indicated in green in Fig. 1. Precipitation data from neighbouring stations show that the main rain season takes place from December to April. The image combinations selected to analyse surface changes will be chosen according to the precipitation information. 3875 978-1-4673-1159-5/12/$31.00 ©2012 IEEE IGARSS 2012