CleanSeaNet network of ground stations

CleanSeaNet uses three polar orbiting SAR satellites: ENVISAT, RADARSAT-1 and RADARSAT-2. ENVISAT provides 405 km swath coverage, and RADARSAT-1 and -2 provide 300 km. Swath coverage refers to the width of the strip covered by the radar at each overpass. The frequency of observations for polar orbiting satellites is significantly greater at higher latitudes than at the equator. Therefore, having access to three wide swath capable satellites mitigates orbit constraints and increases CleanSeaNet flexibility for surveillance operations in support of illegal discharge response chains also at lower latitudes.

Remote sensing radars are used to identify objects and landscapes through the transmission of pulsed microwave (radio wave) beams. The beams bounce off, and are altered by, objects and surfaces they come into contact with (termed backscatter). The backscatter is transmitted back to the satellite, and the strength and origin of these returning reflections is captured by sensors. The resulting data can be analysed to provide information of varying kinds, for example whether a sea surface area has an unusual texture which may be due to spilt oil. Synthetic Aperture Radar (SAR) sensors have enhanced capabilities for transmitting and receiving beams, and therefore produce higher quality images.

Even very thin oil films, some measuring just micrometres, can be visible from space. Nevertheless, it is important to note that CleanSeaNet does not detect "oil spills" but "possible oil spills". This is due to the fact that SAR satellite images cannot provide information on the nature of a spill (mineral oil, fish or vegetable oil, other look-alikes). Discrimination between oil spills and look-alikes require more information and most often on site verification.

Furthermore, SAR imagery allows vessel detection in the images. Like any radar, SAR sensors are able to detect ships due to the reflection of metallic elements on the vessels. A ship will appear as a bright dot on the sea surface. In 2011 vessel detection capabilities, which have become increasingly sophisticated, will become a regular feature of the CleanSeaNet service.

If necessary, SAR sensor images can also be supplemented by optical images. Optical sensors detect reflected sunlight, rather than microwaves. For this reason, they can only be used during daytime and in good weather conditions (free of cloud cover). Pilot projects and activities undertaken in the scope of CleanSeaNet have used optical images, and their future integration as a regular part of the CleanSeaNet service is envisaged in 2011.

Spill detected by CleanSeaNet (left).
Same spill overlaid with SafeSeaNet information (right)