A GPS-Tracked Surf Zone Drifter*

Abstract

A drifter designed to measure surf zone circulation has been developed and field tested. Drifter positions accurate to within a few meters are estimated in real time at 0.1 Hz using the global positioning system (GPS) and a shore-to-drifter radio link. More accurate positions are estimated at 1 Hz from postprocessed, internally logged data. Mean alongshore currents estimated from trajectories of the 0.5-m-draft drifters in 1–2-m water depth agree well with measurements obtained with nearby, bottom-mounted, acoustic current meters. Drifters deployed near the base of a well-developed rip current often followed eddylike paths within the surf zone before being transported seaward.

A novel drifter designed for use with a mounted Acoustic Doppler Current Profiler in shallow environments

“…The drifter was assembled at low cost using off-the-shelf components. A disadvantage of the present system is that drifters need to be closely monitored to avoid loss (a limitation that can be overcome using telemetry, e.g., as on the surfzone drifters used by Schmidt et al 2003).…”

“…The cost and design of these drifters varies depending on the application. Building on deployments of drifters in the deep ocean (e.g., Davis 1985), and taking advantage of cheap and accurate modern GPS systems, researchers have recently developed low-cost drifters for use in nearshore, estuarine (Johnson et al 2003;Austin and Atkinson 2004;Thomson 2012) and surfzone (Schmidt et al 2003;MacMahan et al 2009) environments. However, the drifter designs above typically have drafts of around 0.5 to 1 m, rendering them unsuitable for use in very shallow flows.…”

Temporal observations of rip current circulation on a macro-tidal beach

“…Rip drifter floats were constructed following a design similar to Schmit et al (2003) and their position was monitored at 0.5 Hz using GPS loggers that were post-processed from a survey-grade static base station following MacMahan et al (2009). These provided estimates of rip current flows with an accuracy for position and speed of o 0:4 m and o 0:01 m s À1 , respectively.…”

Pulsations in Surf Zone Currents on a High Energy Mesotidal Beach in New Zealand

“…GPS drifters were based on the design of Schmidt et al (2003) and MacMahan et al (2009). The GPS logger was the QStarz BT-Q100eX, which has a velocity accuracy of ±0.05 m s -1 (Thomson, 2012).…”