How it works
Satellite images are acquired in segments of up to 1 400km and swaths of up to 500km. 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 a number of wide swath satellite platforms mitigates orbit constraints and increases CleanSeaNet's availability 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.
SAR imagery used for oil spill analysis also allows vessel detection since they are able to measure the reflection of bright targets against the sea background. This results in ships appearing as bright dots on the sea surface