Coral Bleaching Detection in the Hawaiian Islands Using Spatio-Temporal Standardized Bottom Reflectance and Planet Dove Satellites
Coral Bleaching Detection in the Hawaiian Islands Using Spatio-Temporal Standardized Bottom Reflectance and Planet Dove Satellites
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DOI：
10.3390/rs12193219
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发表时间：
2020-10
期刊：
影响因子：
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通讯作者：
Yaping Xu;N. Vaughn;D. Knapp;R. Martin;Christopher S. Balzotti;Jiwei Li;S. Foo;G. Asner
中科院分区：
文献类型：
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作者：
Yaping Xu;N. Vaughn;D. Knapp;R. Martin;Christopher S. Balzotti;Jiwei Li;S. Foo;G. Asner
提出了一种利用卫星时间序列数据进行珊瑚白化检测的新方法。虽然由于海底反射率的低信噪比，很难从卫星图像中检测到珊瑚漂白，但我们使用了三种方法克服了这一困难：1)为Planet Dove卫星开发的专门预处理，2)确定基线反射率统计的时间序列方法，以及3)基于先前存在的活珊瑚地图的区域过滤器。时间序列分为基准期(2019年4月至7月)和漂白期(2019年8月至今)，前者是已知没有发生珊瑚漂白的时期，后者是根据实地数据已知发生漂白的时期。漂白周期的确定允许计算每个区域的标准化底部反射比(SBR)。SBR将每周的底部反射率转换为相对于基线反射率分布统计数据的值，从而提高了对漂白检测的敏感度。我们测试了SBR的三个时间平滑尺度(每周、累积平均和三周移动平均)。我们对主要夏威夷群岛珊瑚漂白的实地核查表明，累积平均和三周移动平均平滑检测到珊瑚漂白地点的比例最高，分别正确识别了18个地点中的11个和10个。然而，三周移动平均值在珊瑚漂白检测中提供了更好的灵敏度，性能提高了至少一个标准差，这有助于确定检测到的漂白事件的置信度。
We present a new method for the detection of coral bleaching using satellite time‐series data. While the detection of coral bleaching from satellite imagery is difficult due to the low signal‐to‐noise ratio of benthic reflectance, we overcame this difficulty using three approaches: 1) specialized pre‐processing developed for Planet Dove satellites, 2) a time‐series approach for determining baseline reflectance statistics, and 3) a regional filter based on a preexisting map of live coral. The time‐series was divided into a baseline period (April‐July 2019), when no coral bleaching was known to have taken place, and a bleaching period (August 2019‐present), when the bleaching was known to have occurred based on field data. The identification of the bleaching period allowed the computation of a Standardized Bottom Reflectance (SBR) for each region. SBR transforms the weekly bottom reflectance into a value relative to the baseline reflectance distribution statistics, increasing the sensitivity to bleaching detection. We tested three scales of the temporal smoothing of the SBR (weekly, cumulative average, and three‐week moving average). Our field verification of coral bleaching throughout the main Hawaiian Islands showed that the cumulative average and three‐week moving average smoothing detected the highest proportion of coral bleaching locations, correctly identifying 11 and 10 out of 18 locations, respectively. However, the three‐week moving average provided a better sensitivity in coral bleaching detection, with a performance increase of at least one standard deviation, which helps define the confidence level of a detected bleaching event.