EARSeL eProceedings Vol. 3, No. 1, 105-117, 2004

Abstract
This paper addresses the need for a finer description of coastal zone relief that is currently of interest for benthic habitat mapping. For example, the distribution of seaweed species in the tidal zone will mostly depend on the terrain's hypsometric level, slope and orientation. These parameters can be used in predictive distribution models, or more simply merged with 2.5/3D imagery to enhance interpretation. Since the required accuracy is of the order of 20-30 cm, two remote sensing techniques, lidar and photogrammetry, were examined and conditions for their application were assessed.
Lidar surveys have been shown to provide such accuracy in all instances, whatever the substratum and vegetal cover type, as well as with the slope values currently encountered in tidal zones. Photogrammetric techniques were compared with lidar. They could achieve the required accuracy, provided that two conditions were met: a) the availability of a sufficient number of high quality ground control points, and b) the textural content of the ground observed. Tidal sedimentary areas clearly lack both of these assets, resulting in dramatically reduced accuracy. In mixed zones with hard and soft substrata, a strategy has to be implemented whereby methods are adapted locally to the specific needs of benthos and biodiversity mapping, while keeping in mind the constraints and costs incurred.

ISSN 1729-3782