Satellites • Other remote sensing techniques • Saltmarsh morphology • Vegetation • Species specific studies

Satellites

Relatively detailed, ground-based surveys (such as those undertaken by Burd, 1989; Hemphill & Whittle, 2002; Stark et al., 2002) provide the necessary information to establish change in saltmarsh. Changes may be quite small (a few mm change in level) but, nonetheless, significant. However, such survey is resource intensive and expensive to undertake on a regional scale. Remote sensing can provide the opportunity for more frequent observations, albeit at a coarser scale and to determine longer term changes (decadal).

Satellites (currently under-utilised as a source of information on change in coastal habitats) can cover large areas and record cumulative and significant effects (potentially over a period of weeks). However, they are less useful for measuring more rapid or small-scale change. Until recently, a further impediment was the very coarse scale of resolution that could be obtained (of ten to twenty metres, which limited the level of detail available), but recent improvements in periodicy and resolution has reduced this (in some cases to about a metre) and thus, at a strategic level, the need for more traditional forms of spatial survey might be reduced. However, for this to be achieved there must be a clear relationship established between the satellite imagery and the situation ‘on the ground’. This rectification is achieved by comparison with direct land measurements. In some cases this is needed on an image-by-image basis and so can be less attractive (as the ground survey is needed anyway), however, the larger the area to be covered and the greater the frequency between surveys the more attractive this approach becomes.

The European Space Agency and the EC through the European Environment Agency are currently developing a maritime information system devoted to integrating Earth Observation data into policy and decision-making in the coastal zone (see CoastWatch, which forms one part of a the European Global Monitoring for Environment and Security initiative). It is not clear if this will be developed as a separate initiative or as part of a wider marine information system. However, it could provide a useful source of information at national/regional scales and may be especially valuable in determining the overall status of the saltmarsh resource.