Understanding subsurface patterns of suspended sediment in tidal seas through satellite imagery, South Korea

Abstract

Banded patterns in remotely sensed reflectance can correlate with bathymetry in macrotidal seas. Over ridges, reflectance is higher, and over adjacent channels it is lower. This may be due to faster current speeds at shallower depths. Alternatively, depth-dependant stratification could limit upward mobility of sediment in tidal channels. Evidence of stratification over the Heuksan Mud Belt (HMB) off southwest Korea was examined by analyzing GOCI time series of Rayleigh-corrected reflectance. Reflectance measurements were fitted to a M4 periodic function, simulating flows of the HMB’s M2 constituent tide. Phase lag of peak reflectance in relation to high tide was related to depth, generating regional estimates of vertical eddy diffusion coefficients. The coefficient was consistent with theoretical values of an unstratified environment in the spring and summer, and lower in the fall and winter. This difference suggests seasonal stratification, caused by changes in suspended sediment concentration related to the East Asian Monsoon.