A hydrostatic profiler for nearshore surveying

Abstract

A portable beach-profiling system is described that utilizes the hydrostatic pressure principle to measure vertical differences between a pressure sensor that follows the profile and a reference sensor on the shoreline. The two instruments are connected by a fluid-filled tube. Horizontal distance is determined by measuring the extension of the tube. The complete profiling system, including a data-logging capability on magnetic tape, is carried in a small four-wheel-drive vehicle. Vertical accuracy in ocean surveys is estimated to be 2.5 cm and horizontal accuracy approximately 1 m. This accuracy is sufficient to resolve sediment transport volumes in most applications. Surveying the underwater portion of nearshore beach profiles has presented significant accuracy problems in the past. The highest accuracy is required at the greatest offshore distance to resolve sediment motions. Boat-supported surveying systems, using the sea surface as a horizontal datum, suffer from the presence in the record of surface waves with a broad range of periods which are difficult to remove from the profile. A number of systems have been developed to eliminate the sea-surface intermediate reference and to measure the submerged portion of the profile directly. These systems involve large vehicles that are propelled or pulled along the bottom and are restricted by portability limitations. The system described eliminates many of the portability problems.