Turbulence Measurements with a Moored Instrument.
Abstract
A new, autonomous and moored microstructure measuring instrument has been tested in coastal waters. The instrument measures shear in the dissipation range of the wavenumber spectrum using 4 shear probes, temperature fluctuations using two FP-07 thermistors, temperature and salinity using three pairs of Seabird sensors, horizontal currents using 2 ducted rotors and a fluxgate compass, and body motions using three accelerometers and a pressure transducer. Data are sampled for 128 seconds every 5 minutes and reduced into ensemble and band-averaged spectra and statistical parameters. The processed data are transferred to a disk every 6 hours along with one 128-second set of unprocessed data. In a two-day experiment, the instrument experienced peak flows of 0.15 m (s-1) and resolved dissipation rates in currents as slow as 0.03 m (s-1) Spectra of velocity fluctuations agree closely with the Nasmyth universal spectrum (Oakey 1982). For dissipation rates, the lower limit of detection is determined by electronic noise while the upper limit is set by the angle of attack of cross-stream velocity fluctuations. Both constraints become less restrictive with increasing current. The electronic noise falls below 10-10 W kg(-1) in flows faster than 0.1 m (s-1) for which we detected dissipation rates as low as 4 X 10-10 W kg(-1). The autonomous instrument makes it possible to obtain long time series at much reduced cost compared to conventional profiling from a ship.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1996
- Accession Number
- ADA307229
Entities
People
- D. Newman
- Dingbin Huang
- J. Box
- Rolf Lueck
Organizations
- University of Victoria