Abstract
To achieve high accuracy bathymetry retrieval using remote sensing images with robust performance in a 0 to 25 m-deep lagoon with sharp bottom depth variations, a new Iterative Multiple Band Ratio (IMBR) algorithm is tested against known Multiple Band Ratio (MBR) and Single Band Ratio (SBR) algorithms. The test was conducted using the five multispectral bands, at 10 to 60 m resolution, of a Sentinel-2 image of the 25 km2 Poe lagoon, a UNESCO World Heritage Area. The IMBR approach requires training datasets for the definitions of depth threshold at which optimal band ratios vary. IMBR achieved accuracy, quantified with an original block cross-validation procedure across the entire depth range reached a mean absolute error of 46.0 cm. It compares very favorably against MBR (78.3 cm) and the various SBR results (188–254 cm). The method is suitable for generalization to other sites pending a minimal ground-truth dataset crossing all the depth range being available. We stress that different users may need different precisions and can use MBR or SBR algorithms for their applications. For the hydrodynamic modelling applications that are developing in New Caledonia, the IMBR solutions applied to Sentinel imagery are optimal.
Highlights
Knowledge of bathymetry is a critical issue for many coastal scientific and management applications
In shallow coral reefs and lagoons, bathymetry plays an important role in geophysical and biological processes: living communities, substrate types and habitat zonation are frequently related to water depth [1], sedimentary facies are controlled by depth and energy regime [2,3] and coral bleaching is depth-dependent [4]
We demonstrate the improvements made by our approach by firstly performing different bathymetry estimations (SBR and Multiple Band Ratio (MBR)) on the portion of the lagoon corresponding to the Shallow Lagoon Area (SLA)
Summary
Knowledge of bathymetry is a critical issue for many coastal scientific and management applications. In shallow coral reefs and lagoons, bathymetry plays an important role in geophysical and biological processes: living communities, substrate types and habitat zonation are frequently related to water depth [1], sedimentary facies are controlled by depth and energy regime [2,3] and coral bleaching is depth-dependent [4]. In terms of applied coastal studies, accurate bathymetry is paramount to achieve many applications, from the assessment of coasts facing storms or changing climate conditions [5], to realistic hydrodynamic 3D modelling [6,7] or the exploration of submerged landscapes and archaeological sites [8,9]. Bathymetry is not known precisely everywhere for the 19,385 km of shallow and deep lagoons [12] that surround
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