Plankton survey system

The Plankton Survey System (PSS), developed at the National Oceanic and Atmospheric Administration's (NOAA) Great Lakes Environmental Research Laboratory (GLERL), has been designed to collect high temporal and spatial resolution marine environmental data in three dimensions. The system has proven effective in providing valuable survey information before, during and after sediment re-suspension events in Lake Michigan in support of GLERL's NOAA/NSF funded Episodic Events Great Lakes Experiment (EEGLE) program. The PSS is a towed multi-sensor platform capable of measuring turbidity, chlorophyll a, photosynthetically active radiation (PAR), conductivity, temperature, and zooplankton spatial distributions. All sensors are integrated using a serial data interface. All data are geo-referenced and registered with time, depth, and vehicle pitch, roll, and speed information. A deck unit supplies power for the underwater vehicle components and provides interfaces for data collection and system monitoring. System software provides real-time display of all marine environmental measurements and vehicle status. Zooplankton spatial and individual size distributions are measured using an optical plankton counter (OPC). The OPC measures particle size distributions (0.25-14 mm) using an LED array and a photodiode receiver. Deflections caused by particles crossing the LED generated light beam (4/spl times/20/spl times/100 mm) are detected by the receiver and digitized. Present work is focused on moving the OPC beyond use as merely a survey tool to calibrating the instrument using laboratory and field measurements. Laboratory calibration plans include the use of specified particles to establish a reference and subsequent investigations using live zooplankton samples. A range of issues involving the implications of variations in zooplankton body characteristics on OPC detection threshold, turbidity on OPC signal-to-noise ratio, tow vehicle orientation and vehicle and OPC channel turbulence are also investigated.