In Detail: Recommended Practice Flood Mapping

Efficient monitoring and prediction of floods and risk management for a large river is quasi-impossible without the use of Earth Observation (EO) data from space. As a matter of fact, one of the most important problems associated with flood monitoring is the difficulty to determine the extent of the flood area as even a dense network of observations cannot provide such information. The flood extent information is used for damage assessment and risk management, and benefits to rescuers during flooding; it is also very important for calibration and validation of hydraulic models to reconstruct what happened during the flood and determine what caused the water to go where it did.

SAR (synthetic aperture radar) measurements from space are independent of daytime and weather conditions and can provide valuable information to monitoring of flood events. This is mainly due to the fact that smooth water surface provides no return to the antenna in microwave spectrum and appears black in SAR imagery. SAR data produces a result with limited accuracy in densely populated areas due to the increased amount of backscattering from houses and other objects. In such cases, the use of optical data is advantageous and can be found here.

However, this recommended practice focuses on a simple threshold method for deriving flood extent from SAR imagery.