Monitoring coral reefs by remote sensing techniques and acoustic data as a ground truth reference in Hurghada, Red Sea, Egypt

The Red Sea hosts unique and ecologically significant habitats, particularly coral reefs, which are increasingly threatened by climate-induced bleaching events. To monitor these impacts, Sentinel-2 satellite imagery, with a spatial resolution of 10 m, was utilized for the detection of coral bleaching. Three analytical techniques, supported by advanced image enhancement processes, were employed to evaluate coral reef conditions, with validation from acoustic measurements and in situ observations. First, Empirical Bathymetry (EB) was applied to estimate water depths and was validated against Echo Sounder (ES) bathymetric data. Second, Depth-Invariant Indices (DII) generate benthic habitat maps, cross-validated using Side-Scan Sonar (SSS) backscatter data. Third, the Pseudo-Invariant Features (PIF) technique enabled the assessment of coral bleaching, with confirmation provided through high-resolution imagery captured by a Remotely Operated Vehicle (ROV). The results yielded bathymetric models, habitat maps, and identification of bleaching events following a recorded marine heatwave. A key finding satellite-based remote sensing offers cost-effective alternative to Marine Geophysical Surveys (MGS) for environmental monitoring at scale. This study contributed to the development database to support long-term marine ecosystem monitoring. This research advances progress toward Sustainable Development Goal (SDG) 13: Climate Action , by laying the foundation for an early warning system for coral reef bleaching.