aboard Alaska State Ferries
off-the-shelf oceanographic instruments we designed a system to make
underway measurements of the basic physical variables (water temperature
and salinity), an essential nutrient (dissolved nitrate) for phytoplankton
production, an indicator of phytoplankton concentration (chlorophyll fluorescence),
an indicator of terrestrial runoff (colored dissolved organic matter fluorescence),
and an indicator of the total suspended particle concentration (optical
beam transmittance). The parameters and their instruments are shown in Table
1. The ship's position was measured with a Global Positioning System (GPS)
Table 1. Oceanographic Instrumentation
SBE 38 Digital Oceanographic Thermometer
SBE 45 MicroTSG Thermosalinograph
MBARI-ISUS Nitrate Sensor
WETStar (Chl) Fluorometer
organic matter conc.
WETStar (CDOM) Fluorometer
C-Star Transmissometer (25 cm)
system was designed to operate remotely for days at a time. It automatically
backflushed with fresh water when it sensed the filter clogging. Data were
collected and sent back daily to our laboratory via an Iridium satellite
modem. New instructions could be sent to the system via satellite to change
its sampling criteria and rates. Periodically personnel from the Kachemak
Bay Research Reserve came aboard in Homer, AK, to clean the sensors and
take calibration samples.
The figure below and left shows a system schematic. The instrument seawater
intake line taps off an existing vent for the ship's sea chest. Water passes
through copper-nickel pipe to an in-line temperature sensor, through a coarse
filter to remove marine debris and into a self-contained instrument enclosure.
There water passes through a backflushable filter, a pump and debubbler,
and into the instrument loop. Finally water is dumped into the bilge where
the ship's bilge pumps remove it. A computer in this enclosure governs the
sampling via a LabView program. A second instrument enclosure contains a
marine uninterruptible power supply and a computer to drive a passenger-lounge
information display. The GPS receiver and the
Iridium satellite modem are located near the ship's bridge.
of the instrument system that measures water temperature and salinity,
dissolved nitrate - a nutrient necessary for phytoplankton production,
phytoplankton chlorophyll, terrestrial dissolved organic matter, and
total suspended particle concentration.
boxes on M/V Tustumena. Primary instrument box with pump, tubing,
valves, debubbler and instruments is to the left. Secondary instrument
box is to the right, with uninterruptible power supply and computer
to drive the information display in the passenger lounge. Click to
see a larger photo.