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The all weather day and night imaging capability of radar sensors renders them an excellent tool for deployment in situations of emergencies caused by natural or technological disasters. Orbital radars are particularly useful in such situations, because the ground-based and airborne means can no longer be relied upon when major disasters strike. The relatively simple imaging principles of active radar sensors based on the dielectric properties and surface roughness of the ground targets can generate rapidly information on the areas affected by such disasters as floods, oil spills and lava flows, without requiring a significant amount of image enhancement and value-adding. Consequently, Synthetic Aperture Radar (SAR) sensors onboard several satellites are routinely used for disaster response. One of the best examples of the use of these sensors in an operational mode is the International Charter 'Space and Major Disasters'.
The Charter is in fact the first successful multinational attempt to exploit the benefits of space technologies in managing natural and technological disasters. The Charter is about joint operations and tasking of satellites of the member space agencies of Europe (ESA), France, (CNES), Canada (CSA), the U.S.A. (NOAA/USGS), India (ISRO), Argentina (CONAE), Japan (JAXA), the Disaster Monitoring Constellation (DMC) and China (CNSA) to acquire satellite images, derive products as needed and deliver these within the brief emergency response period to users directly involved in disaster management. The uniqueness of the Charter lies in a single point of contact and a coordinated approach to space supported disaster relief offered by the above space organizations.
After a brief introduction to the Charter operations, the paper goes on to describe a few major events of coastal and inland flooding, oil spills, and lava flows covered by the Charter with its SAR satellites, namely RADARSAT-1, ERS, ENVISAT and ALOS. Together, these SAR systems operating in C or L band offer a good choice of polarization, illuminated swath width, spatial resolution, and look angle, suitable for the extent and type of the disasters being covered. Damage assessment is carried out with post-disaster acquisitions and their comparison with reference imagery derived from the rich SAR data archives of these satellite missions for the purpose of change detection and creation of map products. A variety of products, generated by special software tools for change detection or by means of standard image interpretation techniques, is offered to the requesters. These include flood polygons, lava flow maps, oil slicks on water surface, space maps on various scales, before and after event images, damage maps, and 3-D visualizations. Examples of major disasters related to large-scale inland floods in North America and Central Europe, lava eruptions in Africa, Asian Tsunami and Hurricane Katrina are described with animated slides.
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