Envisat ASAR mosaic of changes in Arctic sea-ice

Satellites carrying SAR (Synthetic Aperture Radar) instruments contributing to GMES include ESA's ERS-2 and Envisat missions, the Italian Cosmo-SkyMed mission, the Canadian Radarsat-2 mission and the German TerraSAR-X and TanDEM-X missions.

Unlike optical systems that rely on reflected solar radiation or thermal radiation emitted by Earth, imaging radar instruments work independently of light and heat. Radar is an active system that transmits a beam of radiation in the microwave region of the electromagnetic spectrum.

SAR can provide day-and-night imagery of Earth. In addition, clouds, fog and precipitation do not have any significant effect on microwaves, so images can also be acquired independent of weather conditions.

The GMES Contributing Missions carrying SAR sensors complement the Sentinel-1 mission, which is due for launch in 2013.

Sentinel-1 operates at C-band to provide SAR imagery at medium resolution. Its wide swath offers fast global coverage. The Cosmo-SkyMed, TerraSAR-X, TanDEM-X and SeoSAR operate at X-band and provide high-resolution imagery. Radarsat operates at C-band and with its follow-on RCM will augment Sentinel-1's revisit capabilities.

ERS and Envisat

ERS-2/SAR
Launched in 1995, ESA's ERS-2 carries a C-band SAR sensor that operates in two modes. The wide-swath mode has a swath of 100 km and spatial resolution of 26 m across track and 6–30 m along track. The wave mode provides small 5×5 km images at 200 km intervals along track.

Envisat/ASAR
Launched in 2002, Envisat is the largest Earth observation satellite ever built. It carries 10 instruments, one of which is the Advanced Synthetic Aperture Radar (ASAR). ASAR operates at C-band and in four modes: image, wave, wide-swath and global monitoring. The ground resolution in the first two modes is approximately 30×30 m. In wide swath mode it is around 150×150m and in global monitoring mode 1000×1000 m.

Cosmo-SkyMed

Cosmo-SkyMed
The Italian Cosmo-SkyMed mission is a four-satellite constellation, each equipped with an X-band SAR sensor. The fourth satellite was launched in 2010. The mission operates in three different modes: StripMap, with a 3040 km swath width and a ground resolution of 3–15 m, ScanSar, with a100×100×200×200 km swath and a ground resolution from 30×30 m to 100×100 m and Spotlight-2 with a10×10 km swath and 1×1 m ground resolution.

COSMO-SkyMed was conceived as a dual-use programme to meet both civil and defence needs. The services derived from Cosmo-SkyMed include surveillance, intelligence, damage assessment, risk management for events such as flood, drought, forest fire and also services pertaining to the marine and coastal environment.

Radarsat-2

Radarsat-2
The Canadian Radarsat-2 was launched in 2007 and follows on from Radarsat-1. The advanced C-band radar imager provides commercially available high-quality data products for many applications. It can operate in a number of modes with resolutions ranging from 3 to 100 m and swath widths from 20 to 500 km.

Radarsat Constellation Mission (RCM) is a Radarsat-2 follow on mission made up of three satellites to be launched from 2014. It will have multiple operating modes with similar resolutions and swaths as Radarsat-2.

TerraSAR-X and TanDEM-X

TerraSAR-X
The German TerraSAR-X was launched in 2007 carries and a high-resolution X-band SAR sensor. TerraSAR-X operates in three alternate operating modes: SpotLight giving 1 m resolution for a surface area of 5×10 km, StripMap giving 3 m resolution for a surface area of 30×50 km and ScanSAR giving 16 m resolution for a surface area of 100×150 km.

The mission was implemented through a public private partnership between the German Aerospace Center (DLR) and Astrium GmbH.

TanDEM-X
The German TanDEM-X was launched in 2010 and is almost identical to TerraSAR-X. The two satellites fly in closely controlled formation with between 250 and 500 m between the two. The mission will provide consistent global digital elevation models with an unprecedented accuracy.

SeoSAR

SeoSAR
To be launched in 2012, SeoSAR is Spain's first high-resolution X-band SAR mission. It operates in three modes: SpotLight with a 10×10 km swath and ground resolution of 1 m, StripMap with a 30×30 km swath and ground resolution of 3 m and ScanSAR with 100×100 km swath and ground resolution of 6×18 m.