Accomplishments & Reports: Physical Oceanography Program

The physical oceanography program aboard R/V Polar Duke during the SANTA CLAµS cruise in December 1994 consisted of two parts; (1) vertical CTD/rosette profiles, and (2) continuous underway monitoring of ocean and atmospheric surface environmental conditions. This field report briefly describes the methodology used and preliminary results.

CTD/rosette program

A Sea-Bird Electronics model 9/11 Plus CTD with a General Oceanics 12-bottle rosette sampler was used to obtain continuous vertical density profiles of the water column, in most cases surface-to-bottom. Additional sensors provided dissolved oxygen, chlorophyll-a fluorescence, beam transmission, downwelling solar radiation (PAR), and light scattering profiles. Fifty-eight such profiles were obtained in the South Pacific, Crystal Sound, Lemaire Channel, Paradise Harbor and the Deception Island caldera. In addition, eleven rosette- mounted 12-liter "GO-FLO" sampling bottles were triggered on each station to collect water samples for the various researchers participating in SANTA CLAµS and for independent salinity and oxygen determinations. Dissolved oxygen was measured using a Sea-Bird (Beckman) oxygen sensor, fluorescence with a Chelsea fluorometer, beam transmission with a SeaTech 25-cm transmissometer, PAR with a Biospherical Instruments 4-π sensor and light scatter with a SeaTech model LS6000.

The SANTA CLAµS underway system

The goal of this program was to acquire essential information on the surface environment while the ship was underway and on-station so that surface expressions of frontal and biological boundaries could be mapped.

The system acquires data from several different sensors and transducers which are part of the Polar Duke's IMET meteorological system and other instrumentation (GPS, gyro compass, bottom depth). With the able assistance of ET Dave Asselin, ASCII messages were provided from each of these systems which were acquired through a multi-port interface card. Real time data were displayed on the PC screen. The ship's LAN network was utilized to link computers and allow simultaneous recording of underway and CTD data on 150 MByte Bernoulli cartridges.

Control was governed by a program written with the Professional Development BASIC BC7 system which performs the following tasks:

• At one-minute intervals, writes data from the combined inputs to a hard disk file in ASCII format. The file is opened and closed each minute to minimized data loss should there be a power failure. Updates the screen each minute with the data in a readable form. When not interrogating the data channels, the positional data on each GPS fix is displayed.

• Continuously updates the distance, time and course to the next station or other waypoint. Calculates the time of the next sun phenomenon (sunrise, local apparent noon and sunset) based on the current ship's position, speed and the time. When all three coincide, the display shows "The sun is setting now," for example. A check outside on those rare days when the sun could be seen in the area, verified the accuracy of these predictions which have been modified by the author from the standard Smithsonian formula.

• Allows operator interactive discourse with the program via softkeys. The most important of these is the entry of comments whenever an event occurs at any time during a cruise. For example, when a CTD station starts, the station number and a short comment can be entered. At this instant, the program collects data from the GPS and all the environmental sensors, keys it to the comment, and records a line in the data file. If standard codes or phrases are used for various events, station logs can easily be produced at the end of a cruise or other intervals.

• Allows review of the last several comments tagged with time and position.

• Certain activities such as bird or mammal observations can be automatically logged at a pre-selected start time and repetition rate. Event number is automatically incremented.

• Raw data values (e.g., DC volts) appearing on certain channels can be read directly enabling calibration at intervals of some instruments such as the transmissometer.

• A brief message can be left on the "message board" for the next watchstander or for general information.

At midnight GMT a new file opens for receipt of the next day's data and records the previous day's file and certain values to the LAN and/or a diskette. This way data can be acquired by other users without interruption to the program.

Two other processes are then initiated using a non-dedicated PC. First, a daily scientific log is printed showing all environmental parameters each hour of the day and whenever a comment was made. A daily summary sheet is printed showing the extremes and means of the major parameters, distance travelled, cumulative distance for cruise, and sun phenomena times. Finally, a daily plot of environmental parameters and ship's track is printed, similar to the real-time plotter output, but "cleaned up" and including times, positions, and designated numbers of all stations and other regular observations done on the cruise.