Sentinel-1 is one element in the GMES (Global Monitoring for Environment and Security) programme, an initiative by the European Commission and ESA to set up a sustainable European network for recording and analysing environmental data. Sentinel-1 will help to monitor and analyse environmental events round the globe.
Astrium will supply the C-band radar for the Sentinel-1 satellite. Weighing some 2.2 metric tons, from 2011 the satellite will orbit the Earth at an altitude of 700 kilometres. Its orbital path will take it across the poles on each orbit, enabling the radar instrument to scan the Earth in 'swathes' as it rotates beneath the satellite. Designed as a successor to the present satellites ERS and Envisat to assure continuity in radar-based Earth observation, Sentinel-1 will observe the Earth from orbit for at least seven years. In contrast to its predecessors ERS and Envisat, however, the radar instrument carried by Sentinel-1 will include improvements such as enhanced antenna performance, which in turn will ensure better data quality.
The Astrium-built C-band SAR (Synthetic Aperture Radar) instrument, which delivers radar images of the Earth’s surface, is the core element of the mission. By taking advantage of the satellite’s flight motion, SAR is able to simulate a considerably larger antenna than is actually present, thus significantly increasing the image resolution. The radar on Sentinel-1 operates in the C band frequency range. The C-band radar beam, which has a wavelength of six centimetres, penetrates forests and scrub to reach the ground, and the C band radar registers any movements or changes on the Earth’s surface to within a centimetre. Sentinel-1 will be equipped with an active antenna made of up 280 individual antennas. The active antenna can be electronically directed towards a new observation terrain without having to be physically moved. Thanks to this technology, several adjacent swathes can be scanned on each overflight and later combined to form a larger overall picture. The radar instrument can operate in four different observation modes which differ primarily in the width of the scanned corridor and the resolution of the radar images. This enables Sentinel-1 to respond to a wide range of varying requirements. In strip-map mode, strips of terrain 80 kilometres wide are scanned at a resolution of 5x5 metres. The interferometric wide-swathe mode registers corridors 250 kilometres wide at a pixel size of 5x20 metres. The extra-wide swathe mode provides a more extensive overview of larger expanses of terrain. In this mode, a corridor 400 kilometres wide is mapped at a resolution of 100x25 metres. The fourth mode, known as wave mode, scans 20x20 kilometre spots at a resolution of 20x5 metres.
Sentinel-1 has been specifically designed to cover a wide range of environmental and security tasks. Observing the melting ice masses in Greenland, for example, should provide important data to help predict rises in sea levels.
