Laboratory Study of ADCP Wave Measurements

Abstract

The National Ocean Service (NOS) collects real-time environmental data to support mission activities including navigation safety, coastal hazard mitigation, and coastal resource management. Near shore wave information is important for these activities and is of growing interest to marine user groups. Acoustic Doppler current profiler (ADCP) are a primary tool for NOS current measurement programs. Recent technology development has added wave measurement capability to these instruments and provided a convenient way for wave monitoring. However, only limited field comparative studies have been conducted. The need to further understand the performance of these instruments and their operation requirements exists. Tests under controlled laboratory conditions offer certain advantages over field intercomparisons including reduced measurement uncertainties, isolation of variables, and is generally cost effective. This paper describes the study of wave measurement performance of a RDI 1200 KHz ADCP in a wave basin with prescribed waves consist of regular, irregular, and multi-directional waves. The steepness and peak energy frequency for each type of waves, and the orientation of ADCP acoustic beams relative to incident waves were varied. A Linear Array of five ultrasonic sensors and a SonTek 5 MHZ ADVOcean instrument were used to provide reference for intercomparison. The ADCP shows good measurement resolutions and agrees well with the reference measurements.