Spatial and temporal variation of water reflectance in an Amazonian estuary: a case study around Tatuoca Island

Abstract. Studies of water color are related to its optically active components, including suspended sediments. The correlation of this parameter with reflectance data is well documented in the literature, to understand its concentrations and transport in the water body. The spatio-temporal variations of water color in an estuary are affected by various physical and hydrological components, which makes it complex to understand. In this study, we sought to understand the spatio-temporal variation of water color, for sampling purposes, in an estuary on the Amazon coast. To achieve our objectives, we applied geostatistical and statistical tools to test the spatio-temporal variability of water color, based on multisensor reflectance data, Landsat-8/9 and Sentinel-2 in the red band. The spatial variation showed distances of more than 48 m ±4.26 at high tide and 44 m ±7.62 at low tide. For the temporal variation, we found that the monthly variations are significant according to seasonality and have the same variation at different stages of the tide. Therefore, the color of the water in the Tatuoca Island region shows geostatistically and statistically significant spatio-temporal variation. The distances and temporal frequency of sampling should be adjusted according to the tides and seasonality to ensure that data is sampled in accordance with the variations in the environment.