Accuracy of IKONOS for mapping benthic coral-reef habitats: a case study from the Puerto Morelos Reef National Park, Mexico

Abstract

Reefs are being threatened by global warming, natural disasters, and the increased pressure of the global population. These habitats are in urgent need of mapping at high resolution so that these threats can be quantified. Remote sensing can potentially provide such quantitative data. In this article, we attempt to map benthic coral-reef habitats at the Puerto Morelos Reef National Park in Yucatan Peninsula (México) and to assess the accuracy of the technique in providing a baseline data for future monitoring of changes and evolution of the reef system. An IKONOS image was used in combination with checkpoint ground sampling and classified using a supervised maximum likelihood classifier (ENVI 4.5). We show that it is possible to map the reef with acceptable accuracy for the lagoon and discriminate the main habitat types, including vegetation, corals, and bare substrate. But, in areas close to the shore and in the front-reef zone, there were significant misclassifications as well as a failure to delineate spatial structures evident on the ground and in aerial imagery. These difficulties and failures occurred either in the areas deeper than 5–8 m where depth limits light transmission (particularly in the red channel) or when the spectral response of habitats were too close to be discriminated. This highlights the need to combine these data with other methods, such as acoustic mapping, in order to provide more accurate representations of the benthic habitats of entire reef systems.

Acknowledgements

We thank all of the people who participated in the acquisition of data in the field. We also thank Rosa Rodriguez-Martinez and Eric Jordan-Dahlgren for providing information from the CARICOMP monitoring; Anastazia Banaszak for providing in situ hyperspectral irradiance data; René Ramos, Raul Aguirre, Mayelihj, Edgar Escalante, Natalia Padilla, Sussana Enriquez, Brigit van Tussenbroek, Maria de los Angeles Liceaga-Correa, Guillem Sòria, Juan-Carlos Jiménez-Muñoz, Cristian Mattar, and Rosa Oltra-Carrió for sharing their knowledge on Puerto Morelos reef and their help in managing and understanding remote-sensing images at the different stages of this work in Mexico City, Puerto Morelos, and Valencia. John Hedley and one anonymous reviewer are thanked for their very useful comments on the manuscript. P. Zapata-Ramírez was funded by CONACyT (Mexico) post-graduate scholarship and P. Blanchon received a grant from CONACyT-SEMARNAT (Project 23749).