Object-based image analysis for mapping geomorphic zones of coral reefs in the Xisha Islands, China
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Object-based image analysis for mapping geomorphic zones of coral reefs in the Xisha Islands, China XU Jingping1, ZHAO Jianhua1*, LI Fang1, WANG Lin1, SONG Derui1, WEN Shiyong1, WANG Fei1, GAO Ning1 1 National Marine Environmental Monitoring Center, Dalian 116023, China
Received 2 August 2015; accepted 25 January 2016 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2016
Abstract
Mapping regional spatial patterns of coral reef geomorphology provides the primary information to understand the constructive processes in the reef ecosystem. However, this work is challenged by the pixel-based image classification method for its comparatively low accuracy. In this paper, an object-based image analysis (OBIA) method was presented to map intra-reef geomorphology of coral reefs in the Xisha Islands, China using Landsat 8 satellite imagery. Following the work of the Millennium Coral Reef Mapping Project, a regional reef class hierarchy with ten geomorphic classes was first defined. Then, incorporating the hierarchical concept and integrating the spectral and additional spatial information such as context, shape and contextual relationships, a large-scale geomorphic map was produced by OBIA with accuracies generally more than 80%. Although the robustness of OBIA has been validated in the applications of coral reef mapping from individual reefs to reef system in this paper, further work is still required to improve its transferability. Key words: object-based, Landsat 8, geomorphic mapping, Xisha Islands Citation: Xu Jingping, Zhao Jianhua, Li Fang, Wang Lin, Song Derui, Wen Shiyong, Wang Fei, Gao Ning. 2016. Object-based image analysis for mapping geomorphic zones of coral reefs in the Xisha Islands, China. Acta Oceanologica Sinica, doi: 10.1007/s13131-016-0921-y
1 Introduction Coral reefs are highly productive ecosystems which are formed from the interaction between the ecological processes that are responsible for the growth of coral and other carbonate producers, and the environmental physical processes such as waves, currents, and sea-level change (Kench, 2013). Lots of studies aim to understand how these processes interaction by detailed geomorphic investigations (Smith and Kinsey, 1976; Perry et al., 2008; Leon and Woodroffe, 2013; Leon et al., 2015), among which mapping regional spatial patterns of coral reef geomorphology provides the primary information to reflect a dynamic balance between constructive and destructive processes in the reef ecosystem. Since the 1970s, coral reef remote sensing has constantly presented new situations with the development of remote sensing technology, playing an increasingly important role in the protection and management of coral reef ecosystems (Xu and Zhao, 2014). As a main application, mapping the geomorphology of coral reefs has been the topic in a great quantity of literature since its inception 40 years ago (Smith et al., 1975; Chen and Teng, 1996; Andréfouët et al., 2001, 2009). In 2003, an unprecedented map of coral reefs worldwide was released by
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