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Journal of Tropical Oceanography

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High-Precision Identification of Coral Bleaching Severity Based on Spectral Proportion Index

HUANG Wei1,2,3, CHEN Qidong1,3,4, LI Zhuli1,3, LIU Xianfu1,3, HUANG Hui2,5, ZHAO Jun6, SUN Shaojie6, HAN Hongyong1,3,7, LI Mingjie1,3,4    

  1. 1. Technology Innovation Center for South China Sea Remote Sensing, Surveying and Mapping Collaborative Application, Ministry of Natural Resources, Guangzhou 510300, China;

    2. National Field Observation and Research Station (Hainan Sanya) for Marine Ecosystem, Tropical Marine Biological Research Station in Hainan, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;

    3. South China Sea Development Research Institute, Ministry of Natural Resources (Remote Sensing Technology Application Center of South China Sea, MNR), Guangzhou 510300, China;

    4. Nansha Islands Coral Reef Ecosystem National Observation and Research Station, Guangzhou 510300, China;

    5. Sanya Joint Laboratory of Marine Science Research, Key Laboratory of Tropical Marine Biotechnology of Hainan Province, Sanya Institute of Ocean Eco-Environmental Engineering, Sanya 572000, China;

    6. School of Marine Sciences, Sun Yat-sen University, Zhuhai 519082, China;

    7. Beijing University of Posts and Telecommunications, School of Computer Science (National Pilot Software Engineering School), Beijing 100876, China




  • Received:2026-04-22 Revised:2026-08-07 Accepted:2026-08-19
  • Supported by:

    Science and Technology Development Foundation of South China Sea Bureau, Ministry of Natural Resources (230208, 23YD05); Key Program of Marine Economy Development Special Foundation of Department of Natural Resources of Guangdong Province(GDNRC [2020]012)

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Abstract: Efficient and quantitative identification of coral bleaching severity remains a critical technological bottleneck for dynamic monitoring of coral reef ecosystems. Current methods predominantly rely on manual interpretation, which suffers from strong subjectivity and insufficient quantification, failing to meet the demands for precise and long-term monitoring. To address this, this study innovatively proposes a method based on the fixed-endmember Spectral Proportion Index (SPI) for identifying coral health status using a newly constructed four-level classification system (Healthy, Bleaching Levels I-III) and a two-level (Healthy/Non-healthy) classification framework. Specifically, based on 1370 in-situ collected coral spectral data samples acquired in 2024, spectral unmixing was performed using sand, coral, and macroalgae as three fixed endmembers to calculate the coral endmember SPI, enabling four-level classification. Results demonstrate a high consistency between coral bleaching severity and the coral endmember spectral proportion. The overall classification accuracy reached 86% (Kappa coefficient = 0.81), with level-specific accuracies as follows: Healthy 80.6%, Level I 94.1%, Level II 75.0%, and Level III 93.5%. In the binary "Healthy/Non-healthy" coarse classification scenario, the SPI method achieved an accuracy of 95.6%, significantly outperforming commonly used remote sensing coral bleaching indices: the Bleaching Chromatic Index (BCI, 82.5%), the Normalized Red-Green Band Difference Index (NRGI, 80.3%), the Normalized Difference Vegetation Index (NDVI, 89.8%), and the Normalized Red-Blue Band Difference Index (NRBI, 32.1%). This study further indicates that the SPI method enables effective quantitative discrimination of coral bleaching severity, providing a simple and reliable new tool for coral status assessment and contributing to the advancement of quantitative coral reef ecological evaluation.

Key words: Coral bleaching detection, Three-endmember spectral unmixing, Spectral Proportion Index (SPI), Quantitative classification of coral health status