TerraSAR-X Rapid Mapping for Flood Events

The use of Earth Observation techniques in the context of hazard management issues has received growing importance in recent years. Due to global climate change the scientific community foresees an increase in the intensity and frequency of extreme weather events, such as hurricanes, floods and windstorms. Specifically, floods already results in estimates of up to 25,000 annual deaths worldwide, extensive homelessness, disaster-induced disease, crop and livestock damage and other serious harm. The nearly allweather capacity constitutes the main advantage of SAR data above optical systems for mapping of flood events. The high resolution, the multi-polarization and multi-incidence angle capability of TerraSAR-X, its quick site access and receiving times open very interesting perspectives for flood mapping, assessment of damages after a hazard. TerraSAR-X data, coupled with the use of optical data and auxiliary data allows getting one step further in the development of information services to better support risk management. The work presented in this paper focuses on the development of an object-based classification approach for operational flood extent mapping in near-real time conditions for TerraSAR-X data. The object-based methodology is implemented in a rule-based environment. Three modules sequentially activated are distinguished in the developed rules system: Segmentation, Water mask extraction and Flood extraction and refinements. The initial (Segmentation) and final (Flood extraction and refinements) modules are automated, while the Water masks extraction process is semi-automated. Two flood events of great intensities that occurred in May 2008 and January 2009, respectively in different environment conditions are used for illustrations. The robustness of the mapping chain is thus tested; the results obtained are compared with ones of a visual interpretation allowing a preliminary validation. The overall study demonstrates the potential of TerraSAR-X data and object oriented methods for the rapid delineation of flood extension maps in an operational environment.