Satellite to assist in flood prevention
Using information gathered by the European Space Agency's Earth Observation satellites, scientists are now able to study, map and predict the consequences of flooding with unprecedented accuracy. The announcement follows the devastating floods in Europe this month, which claimed nearly 30 victims in England, France, Italy and Switzerland, forcing the evacuation of tens of thousands of people. Results are achieved with the help of five tools developed by the ESA: land use maps, imaging of actual flood extents, accurate digital elevation models, soil moisture estimates and a flood modelling computer programme, which combines the data from all of these inputs. The instrument gathering most of the data is the synthetic aperture radar (SAR), flown aboard ERS-1 and ERS-2. The SAR reflects a series of radio pulses off the ground as the satellite flies along its orbital track, and the echoes are translated into a detailed picture of the land below by a sophisticated computer. SAR images can be used to differentiate between different types of terrain, and, ultimately, a detailed digital map. Such maps have many applications. For example, making it possible to calculate exactly how flood waters will behave at any given point on the map: rushing rapidly over steeply sloping tarmac or slowly filling a flat, waterlogged field. The last stage is to use a flood modelling computer programme to create realistic models of real and predicted events. Mathematical simulation techniques are used in this way to allow scientists to create digital rainstorms over the electronic landscape, and monitor what happens. 'What we are doing is creating scenarios for the civil defence authorities' says Jerome Bequignon from the ESA. 'We can show them typical rainfall patterns, or model the overflow of a dam, and then show them typical rainfall patterns, or how the resulting flood will begin and spread. They can then identify high-risk areas which need to be prioritised for evacuation or protection. We can also look at the potential consequences of proposed construction or civil engineering work. In effect, we can tell them that if that supermarket is built there, it is likely to be flooded three years in every ten. This will help them develop prevention plans.'