Deriving particulate backscattering coefficient at 400 nm from small-scale optically shallow waters using Landsat-8...

The particulate backscattering coefficient (b_bp) plays an important role in the growth of coral reefs by influencing the light field conditions. Small-scale optically shallow waters are commonly found in coastal fringing reefs, making it challenging to monitor the spatial and temporal patterns accurately using Aqua satellites with a low spatial resolution. In this study, six existing optimization-based algorithms for deriving b_bp at 400 nm (b_bp(400)) were evaluated with three simulated Landsat-8 (spatial resolution = 30 m) data sets and in situ data from the Luhuitou Peninsula, Sanya. The comparison results indicated that the HOPE (hyperspectral optimization process exemplar) (Fix-H-error or Fix-H-error-free) algorithm which sets an input value of the water depth alone outperformed other algorithms. However, the estimated b_bp(400) from all the algorithms tended to be either overestimated and underestimated due to the improper the spectral shape value of the backscattering coefficient. The HOPE (Fix-H-error) algorithm estimated-b_bp(400) from in situ reflectance also had a good correlation with the in situ total suspended particle concentrations data derived-b_bp(400), with a correlation coefficient of 0.83. Therefore, the HOPE (Fix-H-error) algorithm was selected to estimate the b_bp(400) from satellite-based Landsat-8 data of the Luhuitou Peninsula, Sanya. Time-series (2014-2021) results from these Landsat-8 images reveal the seasonal variation of b_bp(400). The b_bp(400) was low from May to September every year. From October to December or January, b_bp(400) had an increasing trend, and then it decreased until May. Spatial analysis indicated that b_bp(400) decreased with increasing water depth. The spatial and temporal patterns of b_bp(400) were consistent with in situ observations reported in the literature. This study preliminarily showed the efficiency of an optimization-based algorithm in deriving b_bp(400) in small-scale optically shallow water region using Landsat-8 data.