Multi-scale, object-based image analysis for mapping geomorphic and ecological zones on coral reefs

Abstract

Providing accurate maps of coral reefs where the spatial scale and labels of the mapped features correspond to map units appropriate for examining biological and geomorphic structures and processes is a major challenge for remote sensing. The objective of this work is to assess the accuracy and relevance of the process used to derive geomorphic zone and benthic community zone maps for three western Pacific coral reefs produced from multi-scale, object-based image analysis (OBIA) of high-spatial-resolution multi-spectral images, guided by field survey data. Three Quickbird-2 multi-spectral data sets from reefs in Australia, Palau and Fiji and georeferenced field photographs were used in a multi-scale segmentation and object-based image classification to map geomorphic zones and benthic community zones. A per-pixel approach was also tested for mapping benthic community zones. Validation of the maps and comparison to past approaches indicated the multi-scale OBIA process enabled field data, operator field experience and a conceptual hierarchical model of the coral reef environment to be linked to provide output maps at geomorphic zone and benthic community scales on coral reefs. The OBIA mapping accuracies were comparable with previously published work using other methods; however, the classes mapped were matched to a predetermined set of features on the reef.

Acknowledgements

Funding for this work was provided through an Australian Research Council Discovery Grant to S. Phinn and P. Mumby (DP0663) ‘Innovative Coral Reef Mapping’ and through the World Bank Global Environments Facility’s Coral reef Targeted Research programme to P. Mumby and S. Phinn. The fieldwork and data collection would not have been possible without the assistance of Heron Island Research Station and staff, University of South Pacific staff in Suva, Fiji, Palau International Coral Reef Centre, D. Kleine, Dr K. Brady and Dr J. Hedley. OBIA support was provided by Drs K. Johansen and L. Arroyo and Definiens. Quickbird image data were provided by Digital Globe and Geoimage Pty Ltd. We also thank the two anonymous reviewers for their comments which helped us to improve the manuscript substantially.