The primary sensor on the Sentinel-1 satellite is a C-band Synthetic Aperture Radar. This active sensor provides information on ocean, land and ice surfaces and is not impacted by cloud cover. It emits radiation at 5.405GHz and measures the signal scattered back from the surface below the satellite. The strength of the backscatter gives us information on the surface below.
Land applications include mapping and monitoring of agriculture and forestry, mapping of water bodies and flood mapping. Small changes in surface elevation, for example following earthquakes or landslides can be monitored.
Sentinel-1 data is key for the Copernicus Emergency Management Services as the data is acquired and available very quickly and cloud cover is not an issue. The figure shows a map of flooding around Ballinasloe which was generated by the CEMS in the days following a very heavy rainfall event in January 2016.
Backscatter over the oceans and over inland waters can show up surface slicks, due to oil spills or natural processes. Ships can be detected in SAR images, either by their wakes or in contrast to the surrounding waters. SAR is also useful for detecting and measuring swell waves.
Finally, SAR sensors give us information on ice type and concentration in high latitudes and are used for glacier and pack ice monitoring and tracking.