Bathymetry Retrieval Algorithm Based on Hyperspectral Features of Pure Water Absorption From 570 to 600 nm

Current efforts for improving the hyperspectral optimization processing exemplar (HOPE) model include further testing of remote sensing reflectance (R-rs) features containing useful information for bathymetry retrieval via the minimization of the interference stemming from the variability in inherent optical properties and benthic reflectance. In this article, we detected a novel feature originating from the pure water absorption within the narrow spectral region of 570-600 nm. In most coastal regions of clear water in coral reefs, for example, in a coral reefs environment, pure water accounts for the majority of the total absorption in this spectral range. In addition to the depth variation, the spectral behavior of R-rs (570-600) is primarily dominated by a steep increase in pure water absorption with wavelength, whereas the influence of other optical properties, such as phytoplankton/colored dissolved organic matter (CDOM) absorption, particle backscattering, and benthic reflectance, can be simplified using the spectrally constant shape model. An HOPE pure water (HOPE-PW) algorithm using this feature was developed based on R-rs measurements with a spectral resolution of near 3.5 nm, in which only four uncertainties must be resolved. The validation from light detection and ranging (LiDAR) data and comparison with HOPE-bottom reflectance unmixing computation of the environment (BRUCE) using portable remote imaging radiometer (PRISM) data at 15 sites located in five distinct regions of Palau, Guam, Great Barrier Reef, Hawaiian Islands, and Florida Key confirmed that the HOPW-PW algorithm yielded a considerable performance and provided adequate transferability to other sites with varying bottom and water environments. Furthermore, the sensitivity analysis based on Hydrolight-simulated datasets was carried out and showed that HOPE-PW was less affected by variation of bottom types, but still had some limitations in retrieving water optical properties.