Surf-Zone Rip Current Measurements Using Robotic Drifters

Abstract Rip current measurements in the surf zone are essential for understanding nearshore circulation, improving coastal hazard assessments, and refining wave-current interaction models. Traditional in-situ approaches—such as dye tracking, optical imagery, and GPS-enabled drifters—provide valuable but often limited data, as drifters can be rapidly ejected offshore and yield sparse measurements within the surf zone, decreasing efficiency. This study investigates a novel robotic drifter system designed to overcome these limitations by combining high-mobility surface operations with station-keeping and drift-timer modes. These autonomous drifters collect repeat velocity measurements in precisely defined areas, enabling the creation of statistically robust flow fields. Initial results from field experiments at Duck, NC, demonstrate the system’s capacity to resolve fine-scale rip current features, and reveal time-averaged flow patterns. Overall, this robotic drifter system offers a platform for comprehensive, high-resolution mapping of surf-zone currents, facilitating more accurate assessments of rip current behavior and improving safety and operational decision-making in coastal environments.