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

Other remote sensing techniques

The Environment Agency has demonstrated the use of remotely sensed data to map habitats in the coastal environment, particularly in the intertidal zone. These techniques are capable of distinguishing saltmarsh, algae and bare mud, in addition to water and terrestrial vegetation. Thus the general extent of saltmarsh can be mapped using this method. The method employed involves the use of Light Detection and Ranging (LIDAR); an airborne mapping technique which uses a laser to measure the distance between the aircraft and the ground. The technique, used in conjunction with other remote sensing instruments, results in the production of cost-effective terrain maps, which are used to measure land topography and can be used to assess coastal erosion and geomorphology. (The information can also be used to define or characterise land to be set aside for managed realignment). The combination of a terrain map and vegetation coverage (supplemented with habitat survey) can be used to determine if vegetation is at the right niche level in relation to the tidal frame and be used to indicate the way the saltmarsh at a location is functioning.

The Environment Agency has also generated routines to allow for the removal of surface features from the data sets, including vegetation, such that it may be possible to measure gross change in saltmarsh surface levels using successive surveys. Successful measurement of erosion or accretion helps to identify areas that show a net decrease in the area of saltmarsh. It also provides a means of assessing the effectiveness and long term evolution of those areas currently subject to management, particularly where re-creating or restoring saltmarsh is a key component.

Ground-based measurements of saltmarsh vegetation reflectance, using a portable spectroradiometer, can also be used in combination with remote sensing data to inform saltmarsh management (through the provision of a spectral signature), for example, in relation to grazed and non-grazed saltmarshes. This approach can also, with expert interpretation, distinguish different (assemblages of) vegetation, although again ground truthing is probably required. This technique may, however, be particularly valuable where patterns are not easily visible at ground level or when disturbance to ground-nesting birds should be avoided.

In March 2000 a three year project entitled Collaborative Agreement for developing remote sensing techniques for marine SAC monitoring was initiated between English Nature and the Environment Agency’s National Centre for Environmental Data and Surveillance (NCEDS). Three main areas of study were identified that are critical for the use of remote sensing in habitat monitoring: Data preparation and accuracy, Image classification and habitat mapping, and Morphological change. The full report can be downloaded at:
http://www.english-Nature.org.uk/pubs/publication/PDF/552R.pdf