Bar and swash imaging radar (BASIR): A mobile X-band radar designed for mapping nearshore sand bars and swash-defined shorelines over large distances

Few observational techniques are capable of simultaneously mapping the shoreline and nearshore sand bars at high resolution and over large distances, especially during storms when waves are large and visibility is reduced. Proof-of-concept experiments were undertaken to test the feasibility of using X-band radar, mounted on a beach vehicle with dual-channel global positioning system (GPS), to rapidly map the swash and nearshore bars over several kilometers. Bar and Swash Imaging Radar (BASIR), a mobile system developed in collaboration with Imaging Science Research, was evaluated under varying wave heights and storm conditions through comparisons with bathymetric profiles and video along the North Carolina Outer Banks. The video, operated by Oregon State University Coastal Imaging Lab and the U.S. Army Corps of Engineers Field Research Facility in Duck, North Carolina, utilizes a similar technique of time averaging and multiple-image merging to map sand bars. Significant correlation and relatively low root-mean-square differences were found between the video and radar mosaics. Bar and swash imaging radar underpredicted the cross-shore distance of the inner bar relative to measured bathymetric profiles. Measurements collected during a storm with significant wave heights of 3.5 m compared very closely with the results collected 12 hours later when seas had fallen to 2 m. Results suggest BASIR may prove to be a robust observational technique for mapping the evolution of swash-defined shorelines and nearshore bars during storms. At present, limitations to BASIR include (1) alongshore mapping distance constrained by tide fluctuations and (2) the necessity of having wave heights substantial enough to dissipate over the mapped feature.