The outputs from the Clean Seas project fall into three broad categories: specific technical results related to the methodologies developed; information on the state of the environment around the coastline of Europe; and logistic conclusions about the operation of the earth observation system and the deficiencies which impact on the successful exploitation of the satellite data.
Clean Seas has introduced several new techniques for marine remote sensing. An early objective was the exploitation of synergistic observations of the sea surface. Multiple looks at slightly different times have allowed dynamic information to be derived in both the Gulf of Lion and the North Sea. In one study, multiple looks from a single sensor were used to automate the delineation of frontal signatures for efficient use in hydrodynamic modelling; in the other, complimentary sensors dealt with the challenging of persistent cloud cover in a region noted for short time scales over which strong currents and hence sediment loads vary.
The dynamism that complicates satellite image interpretation as well as its assimilation into hydrodynamic models has also been investigated using novel techniques to characterise the turbulence at multiple scales that contribute to the dispersion of pollutants at the sea surface. The challenge of integrating this new information with conventional hydrodynamic modelling remains. A clear contribution will result in combination of multi sensor field inputs to initialise models, routine updates of current vectors and the use of climatological diffusivity maps. These elements will contribute to both the preparation and planning of responses to pollution incidents, and also to the immediate responses required to deal with incidents around our coasts.
All of the analyses in Clean Seas have been based on the study of satellite images of the sea surface. That process took a significant step forward on 15 July 1997 when the first multi-class observations were made over a 2-hour period and allowed some of the dynamics and bio-physics of potentially harmful algal blooms in the Baltic Sea to be laid bare. This single incident has raised many questions about the monitoring of blooms from space but it has also emphasised the value of additional information whilst highlighting the rarity of near-contemporaneous observation. The reliability of monitoring could undoubtedly be improved through greater co-ordination of image acquisitions but co-ordination by space agencies launching new satellites will have to come first.
The need for Clean Seas has been driven by the need for reliable environmental information. The outputs from several elements of the work have resulted in new perspectives on the quality of the environment. Traditionally, earth observation has focused on single anecdotal observations of an event and tried to extract the maximum amount of information for all uses from that data. Clean Seas has taken more of a ‘commodity’ approach by exploiting many observations of the sea surface in order to extract a little information from a selection of scenes where it was relevant and appropriate to do so. The results have been maps of oil spills clearly showing the location of shipping routes and the extent of the problem being faced to eliminate illegal discharges. The strategy of deriving Clean Seas style spill maps has been adopted by a number of groups both in Europe and further afield, and despite initial scepticism about the validity and reliability of the individual observations, the importance of these samples are no longer in doubt. The project has moved on, however, and it has been recognised that there are strong external influences on the such statistics. Recent work by the team has demonstrated ways in which the reliability and consistency in space and time can be developed to the point at which it will meet the needs of the bodies which require such routine information.
Consistent long term archives of colour and temperature data have allowed climatologies to be produced and examined in both the Baltic - looking at algal bloom distributions - and in the Gulf of Lion - looking at variability in space and time of marine biomass. Growing concerns about the stability and long term changes in the local ecosystem as a result of global climate changes have increased the need to understand the subtle long term changes that occur around about us. Substantial variability from one year to the next can easily mask the gradual degradation of an environment. Changes occur in space as well as time as the environment reacts to changing pressures and while in situ observations will continue to show the evolution of conditions at single points, they will not provide the full picture. Work by the Clean Seas team has resulted in several examples of complimentary climatological effects that relate directly to the quality of our marine ecosystems.
Hidden within image data acquired by low earth orbiting spacecraft, there is valuable information. The techniques to extract and interpret that information are becoming more robust, well understood and commonly known. To deliver benefits to the general population and provide a return in terms of improved management of the environment from the substantial investments in space-borne hardware, the ground based logistics that provide access to the data and hence the information requires improvement. Data supplied through Stockholm University and through RAIDS have shown that the process of transporting appropriate data from the satellites to the analysts can be managed efficiently. Involvement of commercial companies such as Orbital Imaging has demonstrated that research objectives can benefit from commercial missions and the importance they attach to the data supply chain. Public space agencies with a focus on the satellite technology rather than the exploitation of data do not appear to be as effective at delivering an acceptable level of service to their customers..
Flexible and ready access to data has been of value to the Clean Seas project and with the plethora of sensors due to be launched in the next few years, multi-sensor synergistic exploitation of earth observation will gradually become a reality. The data used will not necessarily be from satellites that have the highest specifications, or those most comprehensively calibrated before release. Rather, use will be made of those satellites that the customer, in this case Clean Seas, can access when and where it is required in a form which can readily be incorporated into the task a hand. Standardised products will be produced from non-standard datasets, and the commodity of satellite image data will be transformed into decision support tools which will realise the value of the information supplied and justify purchase or license fees for access to the data.
The marginal seas around Europe are complex, dynamic and sensitive environments, they cover a vast area and change rapidly in response to a variety of factors. The ad-hoc earth observing system available today does not provide the necessary coverage to monitor all aspects of this environment - it is unlikely that it ever will. Best use must be made of the resources at our disposal and that means exploiting the strengths of each monitoring technique in order to maximise its contribution. In situ sampling at coastal monitoring stations, airborne and ship-borne campaigns all have important roles to play. They provide the mainstay of environmental information used to manage the ecosystem in which we live. Satellites have different strengths and will not replace conventional monitoring techniques but they certainly have important uses:
Local monitoring can be targeted more effectively and economically as a result of information derived from the synoptic satellite sensors producing consistent long term data;
Subtle changes hidden behind large scale and local variability in the short term can be examined for trends and patterns which may then be traced to anthropogenic or natural sources.
These characteristics are the main strengths of satellite based monitoring systems for marine pollution and hence the main avenue through which value can be realised. Technical limitations of coverage and repeat observation times will can be overcome through volume of observation resulting from many more satellites of each of the three classes - colour, temperature and radar. Until the economics of spacecraft procurement and operation change, coverage will not be comprehensive Clean Seas, however, has demonstrated that the ‘system’ is adequate to derive useful information from the diverse mix of sensors with different characteristics operating today.