1. Introduction The potential of remote sensing for the monitoring of the Earth environment and the detection of its temporal variations is well known. A variety of applications in the fields of flood monitoring, forest fire detection, landslide and subsidence, surface deformation and land cover variations were shown in the last ten years using space optical and radar data. However, the real-time utilisation of spaceborne remote sensing for emergency situations is still a difficult task because of the lack of a dedicated system (constellation) providing a day-today revisit of hazardous areas. Remote sensing data can easily allow for prevention (mapping of hazardous areas, drainage networks and land cover mapping, and precise basin modelling), or a-posteriori evaluation of damaged areas. On a case-to-case basis, one may need to provide cartographic products (maps of damaged and hazardous areas) issued from available satellite data with the shortest delay.