Copernicus Sentinel-1

A radar for Copernicus

Sentinel-1 is the radar mission of the European Union's Copernicus programme, built and operated by the European Space Agency. Sentinel-1A was launched on 3 April 2014 from Kourou on a Soyuz, and Sentinel-1B on 25 April 2016. Ramón Torres was the project manager for the mission, and Pierre Potin the mission manager for the data.

Each satellite carries a C-band synthetic aperture radar, which makes images by processing the echoes of its own microwave pulses as it moves. Because it provides its own illumination, it works at night, and microwaves pass through cloud, which makes it reliable where optical satellites are not.

Ground motion and floods

The satellites image the same area on a regular repeat, each in 12 days and the pair in 6, so that changes between passes can be mapped. Interferometry, comparing the phase of two images, measures ground motion to millimetres, used for subsidence, landslides and earthquakes. The imagery maps floods, sea ice, oil spills and ships.

A power failure ended Sentinel-1B's mission in 2022. Sentinel-1C launched on 5 December 2024 on a Vega-C, and Sentinel-1D on 4 November 2025 on an Ariane 6, restoring the pair.

Free and open

The data are free, full and open, to anyone for any purpose, within hours of acquisition. That policy has produced a large community of users and applications, from national flood services to commercial insurance, and encouraged other agencies to open their archives. The volume is large, and ESA and others offer cloud platforms where the data can be processed without downloading.

Radar changes what can be watched

Before Sentinel-1, radar images of the Earth were scarce and expensive, and flood maps depended on the weather being clear enough for optical satellites. With a free and regular stream, flood mapping, ship detection, glacier monitoring and subsidence mapping became routine services. The data volume is so large that it has pushed users toward cloud processing, in which the code goes to the data and not the other way. That change in practice is probably as significant as the sensor itself, and it applies to every observing system whose archive outgrows a single machine.

Instruments and technologies

• C-band synthetic aperture radar A phased-array antenna of 12.3 metres sending pulses at 5.405 GHz and recording echoes, with an electronically steered beam.
• Interferometric mode Repeat passes from almost the same position give phase differences that measure change.
• Precise orbit determination GNSS receivers and laser retroreflectors allow the orbit to be known to a few centimetres.

The people

• Ramón Torres Project manager of the Sentinel-1 mission at ESA.
• Pierre Potin Mission manager for the Sentinel-1 data.

Timeline

• 2014 Sentinel-1A launched on 3 April from Kourou on a Soyuz.
• 2016 Sentinel-1B launched on 25 April.
• 2022 Sentinel-1B mission officially ends after a power-supply failure.
• 2024 Sentinel-1C launched on 5 December on Vega-C.
• 2025 Sentinel-1D launched on 4 November on Ariane 6.

Key lessons for observation today

• Own your illumination A radar makes its own light, so it works at night and through cloud. Active sensors give reliable coverage.
• Open data policy is a design choice The free and open policy increased use. Licensing decisions are as significant as engineering ones.
• Plan the replacement The programme launched successors as the first satellites aged. Constellations need a replenishment plan.

Sources

• ESA, Sentinel-1 facts and figures
• NASA Earthdata, Sentinel-1
• ESA, Handing over Sentinel-1A (2014)
• Belgian Science Policy, Mapping ground motion at European scale