Detection of Coral Bleaching in Oceanic Islands Using Normalized Bottom Reflectance Change Index From Multispectral Satellite Imagery

Abstract

In the context of global climate change, detecting coral bleaching using high-resolution multispectral remote sensing images is essential. However, the difficulty in obtaining the bottom reflectance spectrum restricts the ability to capture changes in highly heterogeneous coral reefs. Furthermore, the coupling between bottom reflectance and water-column absorption affects inverting bottom reflectance. We propose a normalized bottom reflectance change index (NBRCI) based on time series of quantitatively and physically inverted bottom reflectance without ground data. We compare the results with coral bleaching temperature products to validate change processes. Experimental results from the Landsat-8 images of Kuria Island–Aranuka Atoll and French Frigate Shoals of Pacific Islands from 2013 to 2023 prove that the NBRCI can effectively characterize the degree of change in the bottom and identify the spatiotemporal distribution of coral bleaching and recovery. NBRCI is beneficial for monitoring the health of coral reef benthic habitats at the pixel level around the globe.