Correlation of Remotely Sensed Surface Reflectance With Forcing Variables in Six Different Estuaries. Issue 12 (24th December 2019)

• Record Type: Journal Article
• Authors: Tao, Jing; Hill, Paul S.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 12(2019)
• Page Start: 9439
• Page End: 9461
• Publication Date: 2019-12-24
• Subjects: estuarine particle dynamics -- estuarine classification -- estuarine processes -- remote sensing -- river discharge; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2019JC015336
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: This 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 m a x ) and location (X m a 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 m a x values along the river channel are correlated with river discharge, while the X m a 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 m a x values are correlated with river discharge, but the C m a x 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 m a x values are correlated with tidal stage. The C m a x 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. Plain Language Summary: Estuaries are dynamic environments where river freshwater mixes with seawater. The relative strength of river flow relative to flow caused by ocean tides determines how and where freshwater and seawater mix in estuaries, which in turn affects various processes important to humans, like biological productivity and diversity, harbor siltation, and transport of pollutants. It is a challenge to classify estuaries on a global scale due to limited in situ observations. However, satellite remote sensing observations are able to provide repeated, snapshot views of surface water color over large spatial scale. In this study, we examine the links between estuarine dynamics and remote sensing observations in six different estuaries using satellite imagery. The observations demonstrate that satellite‐derived maximum magnitude and position in surface reflectance, which is related to particle concentration, are correlated with river flow and tidal forcing, which can be used to infer different types of estuaries. Remotely sensed observations can also be useful for inferring the subsurface water mixing and sediment resuspension in estuaries. In addition, the responses of maximum in surface particle concentration and its location to river discharge can be used for satellite‐based estimation of river discharge. Key Points: The spatial and temporal variability of R r s distribution indicate different types of estuaries Remotely sensed observations are useful for inferring the subsurface estuarine processes Reflectance‐based discharge retrieval offers a new potential approach for riverine and estuarine monitoring