Evaluation of Surf Zone Survey Systems during Calm and Rough Sea States

Surveys collected with a 10-m-long lighter amphibious resupply cargo (LARC) vessel and a 3.3-m-long jetski are evaluated by comparison with surveys using the 11-m-tall coastal research amphibious buggy (CRAB) in calm and rough sea states representing the lower and upper operational bounds when considering safety and data quality. The centimeter-level accuracy of CRAB surveys, performed since 1981, is well established. The field test consisted of repetitively surveying two cross-shore profile lines from near the shoreline to 6-m water depth, 700 m offshore. The survey lines were repeated four times by the CRAB and nine to ten times by the LARC and jetski. The CRAB data were averaged to define a reference cross-shore elevation and profile shape to serve as ground truth to determine the accuracy of the LARC and jetski surveys. The two systems compare best with the CRAB surveys on the mildly sloping shoreface, seaward of the nearshore sandbar, where alongshore currents were weakest, depth-limited breaking waves were infrequent, and small-scale morphological features that may not be resolved by the CRAB were minimal. The root mean square (RMS) elevation error between the LARC measurements and the CRAB mean profile was 0.03 m under calm conditions and 0.05 m under rougher conditions, whereas the jetski RMS was 0.09 and 0.10 m, respectively.