Description and evaluation of the Acoustic Profiling of Ocean Currents (APOC) System used on R.V. Oceanus cruise 96 on May 11-22, 1981

Abstract

The underway current profiling system used in this study consists of a microprocessor-controlled data logger that collects and formats data from a four-beam Ametek-Straza 300 kHz acoustic Doppler current profiler, heading from the ship's gyrocompass, and navigation information from a Loran-C receiver and a satellite navigation unit. Data are recorded on magnetic tape and some real time calculations are made. The system was first used on a May, 1981 cruise aboard the R.V. OCEANUS in the western North Atlantic. Horizontal currents were profiled to depths of 100m. Time averaging is required to remove effects of ship motion. Errors in our ability to profile ocean currents are estimated to be 5-10 em s-1 for a ten-minute vector average. An intercomparison is made with a moored vector measuring current meter (VMCM). The mean difference in hourly-averaged APOC and VMCM currents over the four-hour intercomparison is a few mm s-1. Data from a variety of oceanic regimes are presented and discussed: these regimes include two Gulf Stream crossings, a warm core ring survey, and shallow water in a frontal zone to the east of Nantucket Shoals.