HR: 0800h
AN: OS21C-1244    [Abstracts]
TI: The Underway CTD
AU: * Rudnick, D L
EM: drudnick@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD Mail Code 0213, La Jolla, CA 92093-0213 United States
AU: Klinke, J
EM: jklinke@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD Mail Code 0213, La Jolla, CA 92093-0213 United States
AU: Hodges, B A
EM: bhodges@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD Mail Code 0213, La Jolla, CA 92093-0213 United States
AB: The development of the Underway CTD (UCTD) is motivated by the desire for inexpensive profiles of temperature and salinity from underway vessels, including volunteer observing ships (VOS) and research vessels. The UCTD operates under the same principle as expendable probes. By spooling tether line both from the probe and a winch aboard ship, the velocity of the line through the water is zero, line drag is negligible and the probe can get arbitrarily deep. The challenge is to recover the probe, because the line velocity will then equal the ship speed, and line drag may become large. This has proven possible using a Spectra line commercially available for fishing. A number of advantages accrue because the UCTD is recovered rather than expendable. First, the cost per profile decreases as the probe is reused. Second, because the probe is recovered, sensors can be calibrated post-deployment, improving the quality of the observations. Third, the UCTD carries a pressure sensor so depth is measured more accurately than by the drop-rate equation typical for an expendable. The design goal for UCTD was to obtain profiles deeper than 100 m at 20 knots (typical of a VOS). This goal has been surpassed, as we are able to profile to over 150 m at 20 knots, and to over 400 m at 10 knots. The first fully operational use of UCTD occurred during a cruise May-June 2004, whose purpose was to examine the effect of internal waves and spice on long-range acoustic propagation. The primary goal of the cruise was to deploy four acoustic moorings on a 1000-km path in the central North Pacific subtropical gyre. UCTD was used while the ship steamed at 10-13 knots between moorings. A total of 97 UCTD casts were completed along the path, resulting in a hydrographic section with a resolution of 10 km horizontally and 5 m vertically. The section clearly showed the effects of thermohaline variability on sound speed.
DE: 4294 Instruments and techniques
DE: 4594 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting