An improved method for thermal stress detection of coral bleaching in the South China Sea
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摘要: 近年来受全球气候变暖等因素的影响,全球珊瑚礁白化事件频发,而美国国家海洋和大气管理局(National Oceanic and Atmospheric Administration,NOAA)的珊瑚礁监测(Coral Reef Watch, CRW)系统在南海的监测结果存在低估问题。文章基于1985年起的180例南海及周边海域的珊瑚礁白化相关报道,通过计算不同阈值组合的白化漏检率、误检率与准确率,评估得到最佳阈值组合,最终实现对南海珊瑚礁白化热应力检测的改进。实验结果表明: ①NOAA阈值对应的白化检测结果漏检率为70.70%,长期的白化低估现象确实存在; ②采用改进后的临界阈值(critical threshold,CT)与警报阈值(alert threshold,AT),可将白化检测准确率由58.13%提升至73.90%,同时漏检率与误检率均低于30%。通过2007年6月南沙群岛的白化事件,发现相较过去的低估,改进后的热应力指数能对事件做到有效检测,并能适时标记白化警报级别。结果证明热应力检测的改进方法能提高珊瑚白化监测水平,有利于南海珊瑚礁的管理与保护。Abstract: In recent years, coral bleaching events have frequently occurred globally due to global warming and other factors. However, the Coral Reef Watch (CRW) program established by the National Oceanic and Atmospheric Administration (NOAA) has underestimated the actual situation of coral bleaching in the South China Sea. Based on 180 cases of coral bleaching in the South China Sea and its surrounding waters since 1985, this paper obtains the optimum threshold combination by calculating the false negative rate (FNR), the false positive rate (FPR), and the accuracy (ACC) of different threshold combinations, thus improving the detection accuracy of coral bleaching events in the South China Sea. The results are as follows: (1) The FNR of the bleaching detecting results obtained using the NOAA threshold was 70.70%, indicating the long-term underestimation of the coral bleaching; (2) With the optimized critical threshold (CT) and alert threshold (AT), the ACC was improved from 58.13% to 73.90%, meanwhile the FNR and FPR were both less than 30%. As revealed by the coral bleaching event in the Nansha Islands in June 2007, the optimized thermal stress index can be used to effectively detect the event and mark the bleaching alarm level in time compared to the past underestimation. Therefore, the improved method for thermal threshold detection can improve the monitoring level of coral bleaching and are conducive to the management and protection of coral reefs in the South China Sea.
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Key words:
- coral bleaching /
- the South China Sea /
- remote sensing /
- SST /
- thermal stress /
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