Accession Number : ADA302498

Title :   ADCP Measurements from the ICESHELF 94 Experiment.

Descriptive Note : Technical rept.,

Corporate Author : WOODS HOLE OCEANOGRAPHIC INSTITUTION MA

Personal Author(s) : Plueddemann, Albert J. ; Galbraith, Nancy R.

PDF Url : ADA302498

Report Date : SEP 1995

Pagination or Media Count : 88

Abstract : The ICESHELF 94 Experiment was conducted during April of 1994 from an ice camp in the Lincoln Sea at approximately 84 N, 63 W. An Acoustic Doppler Current Profiler (ADCP) was operated at the camp from 8 to 24 April in order to characterize the internal wave field at the site. The ADCP was suspended below the ice with transducers facing downwards from a depth of 12 m. This report describes the ADCP configuration and presents the raw data recorded by the ADCP. The processing steps involved in computing horizontal velocities in geographic coordinates from the raw data are described, and time series and spectra of the resulting velocity data are presented. Horizontal velocities of good quality (estimated precision of about 1 cm per second) were obtained between 27.7 m and 137.0 m depth with 7.8 m resolution. Data were obtained at five minute intervals, but averaged to 1 hr during processing to suppress instrument noise. Spectra show the velocity field to be dominated by variance at semi-diurnal frequency, with a maximum in energy between 50 and 110 m depth. The semi-diurnal tidal frequency (M2 = 0.0805 cph) cannot be distinguished from the local inertial frequency (f = 0.0829 cph) in the records. Maximum amplitudes of 8 to 10cm per second were seen near 80 m depth. Velocities from an InterOcean S4 current meter deployed at the same site were compared to those from the ADCP. Typical comparisons showed component velocity differences with means of less than 0.5 cm per second and standard deviations from 1.0 to 1.5 cm per second. The largest differences were associated with peaks in the semi-diurnal oscillations, with the S4 underspeeding relative to the ADCP.

Descriptors :   *OCEAN CURRENTS, *UNDERWATER ACOUSTICS, *SEA ICE, VELOCITY, OCEAN WAVES, OCEAN SURFACE, ACOUSTIC WAVES, COMPARISON, SIGNAL TO NOISE RATIO, TIME SERIES ANALYSIS, ACOUSTIC DETECTION, BACKSCATTERING, DEPTH, OCEANOGRAPHIC DATA, CONTINENTAL SHELVES, PROFILES, MIXED LAYER(MARINE), SALINITY, SONAR ECHOES, ACOUSTIC DATA, SONAR TRANSDUCERS, DIURNAL VARIATIONS, INTERNAL WAVES, DOPPLER EFFECT, OCEAN TIDES, ARCTIC OCEAN.

Subject Categories : Physical and Dynamic Oceanography
      Acoustic Detection and Detectors

Distribution Statement : APPROVED FOR PUBLIC RELEASE