Correlation of Remotely Sensed Surface Reflectance With Forcing Variables in Six Different Estuaries

Abstract

AbstractThis study examines the links between estuarine dynamics and longitudinal distributions of remotely sensed reflectance in estuaries. Reflectance at 655 nm from Landsat‐8 correlates with in situ measurements of surface turbidity. Images collected from 2013 to 2018 are used to investigate the spatial and temporal characteristics of reflectance distribution in six selected estuaries with different dynamics. The results show that the maximum magnitude (C ) and location (X ) of the reflectance are functions of two major forcing variables, the freshwater discharge and tidal stage. Salt wedge estuaries (i.e., the Fraser River, Connecticut River, and Columbia River estuary) are affected strongly by river discharge and are relatively less affected by tidal forcing. In salt wedge estuaries, the C values along the river channel are correlated with river discharge, while the X values generally are not. In partially mixed to strain‐induced periodic stratification (SIPS) estuaries (i.e., Delaware River) and SIPS‐to‐well‐mixed estuaries (i.e., Gironde estuary), the X values are correlated with river discharge, but the C values are not. SIPS‐to‐well‐mixed estuaries (i.e., Gironde estuary) and highly time‐dependent salt wedge to well‐mixed estuaries (i.e., Merrimack River estuary) are affected by tidal forcing. In these estuaries, the C values are correlated with tidal stage. The C values tend to be lower around high tide than low tide. Overall, the results demonstrate that remote sensing observations of ocean color can be utilized to infer subsurface estuarine processes. Satellite ocean color is a potential tool to monitor river discharge and to classify estuaries.