Over three years, the Clean Seas project team has focused on the problem of monitoring marine pollution and the role that earth observing satellites might play. Starting from the concept of the existing scientific satellites being an ad-hoc system, the project has examined synergy within the data from radar, optical and infrared sensors. In conjunction with hydrodynamic models and routine data acquisition from a range of satellites, the team has examined three test sites in detail during a two-year acquisition campaign. The test sites in the Baltic Sea, the North Sea and the north-western Mediterranean around the Gulf of Lion, have produced a number of significant results.
The three test sites were selected for their varied environmental risks and susceptibilities as well as the challenges that they presented from a space-borne monitoring perspective. The team, comprised of experts in the individual disciplines required to analyse and exploit the particular sensor data, has made numerous contributions to the discipline of marine pollution monitoring from space, including:
With a strong emphasis on local monitoring, river outflows have been tracked, for example to improve modelling of heavy metal transport from the Rhine and of surface pollutants in the Mediterranean. Climatological work has also examined the variations in biomass obtained from consistent, long-term monitoring.
The project objective of "assessing the effectiveness of the earth observation system for routine pollution monitoring" has resulted in an opinion that earth observation has a significant contribution to make to routine pollution monitoring. The main strengths of the technique lie in the wide, synoptic coverage that results in consistent results over large areas. Repeatability of results due to extensive calibration activities of single instruments also play a role in ensuring the usefulness of the image data.
Ultimately, the decision made by the environmental manager must be recognised as the point at which any value in a satellite image is realised. To this end, statistics and indicators based on routine, repeated observation are thought to be a key requirement. To deliver this value, the earth observation sector must have reliable and straightforward access to data from well managed archives that respond promptly and accurately to requests.
Single sensors are unlikely to provide adequate temporal and spatial coverage at adequate resolution for pollution monitoring, therefore networks of sensors are required which are co-ordinated in terms of the data formats, quality control information and distribution, in addition to initial acquisition. In the marine environment, conditions change rapidly and features are frequently obscured by cloud, thus requiring multiple looks.
Systematic, routine monitoring of marine pollutants and the dynamic systems that transport them require inputs of colour, temperature and radar data in ways that take advantage of their respective strengths. The contribution of the earth observing system to routine monitoring of marine pollution can be both directly through observation of the pollutant, e.g. algae in the Baltic or oil in the Mediterranean, and indirectly through the dynamic signatures extracted, e.g. in the North Sea to assist modelling the trajectory of known pollutants. Although earth observation has definite strengths, it has weaknesses too and these must be addressed when considering the monitoring of a cloudy temperate area with optical or infrared data or looking for oil slick in predominantly calm or windy locations. Earth observation is a valuable tool, but only when used appropriately.