**Abstract Text**
The transport process in coastal areas, involving kilometer-scale mixing dynamics through barrier islands, requires large-scale current mapping. Although acoustic Doppler current profilers (ADCP) and surface drifters provide in situ measurements of ocean currents, the effectiveness in time, cost, and human resources is significantly reduced when requiring large-scale measurements. Near real-time surface current measurements from high-frequency radar (HFR) are also limited by low spatial resolution in 100’s of meters to kilometer scales. Remote-sensed measurements of surface flows using Unmanned Aerial Systems (UAS) have recently gained considerable attention among research institutes for their cost-efficiency and versatility. In this study, we computed surface currents from UAS video images using a 2D space plus time Fourier transform method linked to the Doppler-shifted dispersion relation fitting technique for surface gravity waves (Streßer et al., 2017). The resulting vector fields visualize the flow structures of the tidal currents through the Galveston Bay inlets, TX in flexible spatiotemporal resolution. We collected twenty-two UAS aerial video recordings at nadir at four different locations near the Galveston Bay entrance during a flood and ebb tide. The UAS wave-based current mapping technique was validated using In situ measurements of the tidal currents by ADCP. The estimated surface currents showed a good agreement with the ADCP measurements with root-mean-square errors of 0.07 m/s in magnitude and 17° in direction. The major limitations of yielding reliable currents were contamination by high concentration of scattered floating objects (e.g., boats and foams from wave breaking) and restriction of the flight altitude at 120 m.



**Abstract Text**
The transport process in coastal areas, involving kilometer-scale mixing dynamics through barrier islands, requires large-scale current mapping. Although acoustic Doppler current profilers (ADCP) and surface drifters provide _in situ_ measurements of ocean currents, the effectiveness in time, cost, and human resources is significantly reduced when requiring large-scale measurements. Near real-time surface current measurements from high-frequency radar (HFR) are also limited by low spatial resolution in 100’s of meters to kilometer scales. Remote-sensed measurements of surface flows using Unmanned Aerial Systems (UAS) have recently gained considerable attention among research institutes for their cost-efficiency and versatility. In this study, we computed surface currents from UAS video images using a 2D space plus time Fourier transform method linked to the Doppler-shifted dispersion relation fitting technique for surface gravity waves (Streßer et al., 2017). The resulting vector fields visualize the flow structures of the tidal currents through the Galveston Bay inlets, TX in flexible spatiotemporal resolution. We collected twenty-two UAS aerial video recordings at nadir at four different locations near the Galveston Bay entrance during a flood and ebb tide. The UAS wave-based current mapping technique was validated using _In situ_ measurements of the tidal currents by ADCP. The estimated surface currents showed a good agreement with the ADCP measurements with root-mean-square errors of 0.07 m/s in magnitude and 17° in direction. The major limitations of yielding reliable currents were contamination by high concentration of scattered floating objects (e.g., boats and foams from wave breaking) and restriction of the flight altitude at 120 m.



Large-scale Current Mapping Using Unmanned Aerial Systems Imagery at Galveston Bay, TX (Room 322, Monday June 26th, 1:30pm-3:00pm)

Engineers, researchers, and climate scientists share developments and innovative practices in the water engineering industry. The Technical Committee for Hydraulics Measurements and Experimental Methods (TCHMEM) of EWRI has organized the HMEM conference six times since 1994, when the first HMEM conference was held in Buffalo, NY. Since then, successful conferences were held in Estes Park, Colorado (2002), Lake Placid, New York (2007), Snowbird, Utah (2012), and Durham, New Hampshire (2017).