Improving the Synoptic Mapping of Coral Reef Geomorphology using Object-based Image Analysis

International Journal of Geographical Information Science International Journal of Geographical Information Science, Volume 25, Issue 6, 2011

Javier Leon and Colin D. Woodroffe

“Monitoring coral reefs is of great importance for environmental management of these ecosystems. The use of remote sensing and geographical information systems enables rapid and effective mapping of the geomorphology of reefs that can be used as a basis for biodiversity and habitat assessments. However, pixel-based approaches have not been appropriate for detailed mapping of such complex systems. An object-based image analysis (OBIA) approach was used in this study to map intra-reef geomorphology of coral reefs across the Torres Strait region using Landsat ETM+ imagery. By combining image analysis techniques and a non-parametric neural network classifier and incorporating additional spatial information such as context, shape and texture, the accuracy of the segmentation and classification was improved considerably.

Qualitative assessment of segmentation. (a) Segmentation based on Landsat image (30 m) (red outlines) and (b) pan-sharpened image (15 m) (blue outlines). Arrows show examples of under-segmentation on the coarser-resolution image when compared to the reference data derived from a Quickbird image (black outlines) over the western end of Bet reef platform. Clouds and shadows appear masked (stippled areas).

“A large-scale synoptic map of 10 geomorphological classes was produced for Torres Strait with an overall accuracy of 75%. The OBIA approach employed in this research has enabled the geomorphology of reef platforms to be mapped for the first time at such accuracy and descriptive resolution.”