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Biophysical Observations aboard Alaska State Ferries
Using 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) satellite receiver.

Table 1. Oceanographic Instrumentation
Variable Measured
Instrument
Water temperature Sea-Bird SBE 38 Digital Oceanographic Thermometer
Salinity Sea-Bird SBE 45 MicroTSG Thermosalinograph
Dissolved nitrate concentration Satlantic MBARI-ISUS Nitrate Sensor
Chlorophyll concentration WET Labs WETStar (Chl) Fluorometer
Dissolved organic matter conc. WET Labs WETStar (CDOM) Fluorometer
Particulate concentration WET Labs C-Star Transmissometer (25 cm)

The 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.
System diagram of data collection boxes on M/V Tustumena for GEM/FOCI ferry data collection
A schematic 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.

 

 

Two instrument 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.

Image of two instrument boxes on M/V Tustumena. Click for larger image.
FOCI/GEM Technical Info FOCI/GEM Data FOCI/GEM Program Information FOCI-GEM (Gulf Ecosystem Monitoring System) Fisheries-Oceanography Coordinated Investigations (FOCI) Pacific Marine Environmental Laboratory (PMEL) National Oceanic and Atmospheric Administration (NOAA) National Oceanic and Atnospheric Administration (NOAA) Fisheries-Oceanography Coordinated Investigations (FOCI) Pacific Marine Environmental Laboratory (PMEL) FOCI/GEM Technical Info GEM/FOCI Biophysical Data index page FOCI/GEM data FOCI/GEM Program Info

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last updated 6/30/2010