Low-cost digital elevation model for marine protected areas

Abstract

Digital Elevation Models (DEM) are essential for a better comprehension of different terrains, as they represent the original geomorphology, and through processing, such as color classification of data, shaded relief, slope, direction of faces and curvature, allows for a range of transdisciplinary interpretations of great value to the management of conservation areas. Mona Cagarras is the chosen spatial area and has positive and negative altimetry amplitudes. For such a fully protected Conservation Unit (CU), remote sensing mapping is an adequate tool for data acquisition, causing no direct interference to the sensitive environment. Existing topographic and bathymetric data do not attend management’s needs for precision, as the altimetric data are scattered and little detailed. The bathymetric DEM was produced from a field survey, using a commercial echo sounder attached to a GPS, with the modeling of the continuous surface done by the Topo to Raster interpolator. For the topographic DEM, three methodologies have been tested: SRTM 30m, ASTER GDEM and survey-based stereophotogrammetry. The resulting DEMs were compared to 23 ground control points and analyzed for their appearance. The stereophotogrammetry best caught the altimetric amplitudes and the winding relief, and proved to be more similar to the original geomorphology. The final DEM corresponds to the sum of the bathymetric DEM and stereophotogrammetrical topographic DEM. The interpolator Topo to Raster generated a submetrical RMS of 0.98m. The large range of bathymetric detail is of huge importance in marine protected areas, as they are the basis to the knowledge of ecosystems. This paper presents a low cost methodology and has potential to become widely applied to aid management in marine protected areas.