Design and development of a low-cost GNSS-tracked surface drifter for investigating tidal currents in a creek environment

Abstract

The tidal dynamics in estuarine and creek environments are quite complex and depend primarily on tides, waves, wind, water depth, and riverine inflow conditions. A proper understanding of tidal dynamics is very essential in terms of estuarine circulation, mixing and dispersion of pollutants and effective estuarine management. Lagrangian-based monitoring provides spatial and temporal variability compared with Eulerian-based measurement system. The present study proposes a low-cost Global Navigation Satellite System (GNSS) tracked shallow water surface drifter, developed considering minimal wind slip, higher submerged drag force, and low heave accelerations for different designs. A drifter design with four vertical fins and two damping discs attached at the top and bottom satisfied the design criteria and has been used in this study. A low-cost GNSS receiver u-blox Navigation Engine On-board (NEO) M8N was installed in the surface drifter considering the relative position error, velocity variability, and satellite visibility employing an Android smartphone-based GNSS receiver. Low-cost GNSS receiver recorded low positional error and low-velocity variability, and a higher percentage of satellite visbility was recorded during the stationary test. Field deployments were conducted with the surface drifter for different months. The estimated surface tidal current velocity showed monthly variability and was dependent on the tidal phase. Further, the trajectory of the surface drifter could properly identify the changes in flow direction across the creek due to phase shifts from high to low tides. The developed low-cost GNSS-tracked surface drifter can be effectively used to monitor the surface tidal dynamics in the creek environment.