The Sentinels are a fleet of European Space Agency (ESA) satellites designed to acquire measurements from multiple sensor types that will provide information necessary to meet Europe's Copernicus Programme objectives. 

The first mission in the series, the Sentinel-1 constellation, includes twin satellites that each carry C-band synthetic aperture radar (SAR) and together provide all-weather, day-and-night imagery of Earth's surface. Sentinel-1A was launched on April 3, 2014, and Sentinel-1B on 25 April 2016. They orbit 180° apart, together imaging the Earth every six days.

The Sentinel-1 constellation benefits numerous services, such as monitoring of Arctic sea-ice extent, routine sea-ice mapping, and surveillance of the marine environment. Applications include oil-spill monitoring and ship detection for maritime security; monitoring land-surface for motion risks; mapping for forest, water, and soil management; and mapping to support humanitarian aid and crisis situations.

In December 2021, an anomaly in the power supply of Sentinel-1B caused the SAR sensor to stop working. Attempts to restore power to the sensor failed, and the mission officially ended on August 3, 2022.

Sentinel-1C was launched in December 2024, reestablishing a twin satellite constellation with extensive worldwide coverage and, in most areas, six-day repeat-pass observations.

All products from the Sentinel-1 mission are available to download from NASA's Alaska Satellite Facility Distributed Active Archive Center (ASF DAAC) through the Vertex search application, programmatically using asf_search and SearchAPI, and through Earthdata Search.