Nearshore Survey System Evaluation

This report evaluates the accuracy of two systems for surveying the beach and nearshore zone. The 10-meter (m)-tall Coastal Research Amphibious Buggy (CRAB) and the 10 m long Lighter Amphibious Resupply Cargo (LARC). The accuracy of the CRAB, in operationsince 1981, to do centimeter-level surveys is well established. The main objective of this evaluation was to determine how well data collected with the LARC, under ideal survey conditions, compared to the CRAB. The field test consisted of repetitively surveying twoprofile lines (777 and 823): four times by the CRAB, nine times by the LARC. An all terrain vehicle (ATV) was used to survey the subaerial beach. The CRAB and ATV data were averaged to define a reference profile shape for use in determining the accuracy of theLARC surveys. The two systems were found to compare extremely well with a mean difference of 1 centimeter (cm), well within measurement accuracy. The two systems compare best on the mildly sloping, shore-parallel shoreface, seaward of the nearshore sandbar where the two measuring systems differ least. The root mean square error between the LARC measurements and the CRAB mean profile was 2.2 cm.