The European Copernicus program's constellation of Earth observation satellites providing free, open data for environmental monitoring. Sentinel-1 (SAR) and Sentinel-2 (optical) are particularly important for water resource applications.
The Sentinel satellite series is the space component of the European Union's Copernicus Earth observation program, operated by the European Space Agency (ESA). Sentinel-1 carries a C-band SAR instrument providing all-weather, day-and-night imaging at 5-20 m resolution with a 6-12 day revisit cycle, critical for flood mapping and soil moisture monitoring. Sentinel-2 carries a multispectral imager with 13 bands at 10-60 m resolution and a 5-day revisit cycle, complementing Landsat for water body mapping, water quality assessment, and vegetation monitoring. Sentinel-3 carries ocean and land colour instruments plus altimeters for monitoring coastal and inland water bodies, sea surface temperature, and lake/river levels. The free and open data policy, combined with systematic global coverage and higher spatial and temporal resolution than many predecessors, has made Sentinel data central to operational water resource monitoring. Sentinel-2's red-edge bands provide enhanced vegetation characterization capabilities useful for riparian corridor assessment and wetland classification. The Copernicus Emergency Management Service uses Sentinel data for rapid flood mapping and damage assessment during disaster events across Europe and internationally.