Surface Water Extent

EO Capability Benefits

Mapping the extent and permanence of surface water bodies using Earth Observation provides valuable information on the impacts of human activities such as land use conversion and climate change on water resources. While seasonal cycles cause natural fluctuations in water levels, long-term climate impacts from rising temperatures, glacial melts to changing precipitation patterns can significantly affect water availability. Earth Observation can differentiate between permanent and non-permanent water bodies, and help quantify the frequency, timing and location of maximum or minimum extents.

EO Capability Description

Surface Water Extent provides the minimum and maximum extents, the water cover frequency and water body classification for surface water bodies within a defined Area of Interest and time period. Since it partially relies on Synthetic Aperture Radar (SAR) imagery, the EO capability can be applied under cloudy conditions but achieves best results with minimal cloud cover as optical imagery, e.g. from Sentinel-2, is used to enhance its thematic accuracy. Water bodies should not be covered by dense vegetation. This EO capability works reliably for water bodies greater than 500m². Linear features such as rivers are detected less reliably than broader water bodies such as lakes. It is most suited for multi-year analyses to detect trends outside of seasonal effects.

Relevant EO Technologies

SAR

HR OPTICAL

Synthetic Aperture Radar (SAR) sends out microwave pulses and coherently combines their echoes along the satellite’s flight path to “synthetically” create a very long “virtual antenna”, generating sharp images–independent of daylight and largely independent of clouds–even though microwave radar uses much longer wavelengths than visible light. Changes in backscatter amplitude (i.e. the strength of the returned signal) reflect variations in surface roughness, geometry, moisture and dielectric properties (and, over land, vegetation structure). When complex images from two (or more) acquisitions are interferometrically compared (e.g. with InSAR), differences in phase—after accounting for topography and atmospheric effects—reveal surface deformation or ground displacement along the radar line of sight.

EXAMPLES

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