Characterization of Tidal Inlet Exchange Flows Using Satellite Imagery

Abstract

We present a satellite-based classification scheme for the main characteristics of large-scale starting jets interacting with coastal currents at Galveston Bay inlet, Texas, using satellite imagery from Sentinel-2 and the Moderate Resolution Imaging Spectroradiometer (MODIS). The Sentinel-2 satellite image analysis identifies two types of tidal starting-jet vortex structures: a shallow single or dipole vortex. The type of starting-jet vortex that forms depends on the propagation path of the tidal jet, given by the angle between the jet and inlet axis, and the tidal dynamics, summarized by an inlet Strouhal number. We show a correlation between these metrics that predicts when the dynamics of vortex formation is dominantly governed by the offshore currents, causing a single-vortex, or the ebbing fluid flow, forming a vortex dipole. By comparing the deflection angle of the tidal jets with local wind observations, we deduce that along-shore currents are the dominant mechanism responsible for the jet deflection and vortex types. Validation of the classification scheme using MODIS satellite images reported up to 94% agreement between the classification scheme and the observed flow type. Comparison of the Sentinel-2 satellite images with empirical equations from laboratory experiments showed good agreement for vortex spin-up time and the diameter of the vortex core.