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The Video Plankton Recorder (VPR) is an underwater video microscope that images plankton and particles in the size range from 0.1 mm to 1 cm. The VPR system automatically identifies the plankton and displays their distributional patterns in real time. The VPR is eight feet long and six feet wide. It is comprised of an aluminum frame covered in a fiberglass skin. It weighs 900 pounds on land, and one hundred pounds in water.
The figure shows the various components of the new VPR system. The steel tow bridle-shown in black, with shadows representing the range of motion-is attached to the forward midpoint of the wing spar, and protrudes from the left side of the nose cone. Researchers use this bridle to tow the VPR behind a vessel. As the VPR moves, so does the arm to compensate movement.
A digital video camera is housed in the nose cose, and a strobe is in the right wing tip. The volume imaged by the VPR is in undisturbed open water between the camera and strobe. The tail fins and rudder are controlled by the flight-control computer and cause the VPR to undulate between two selected depths, or follow a constant depth. They enable the instrument to move off to the side, out of the ship's wake when sampling near the surface.
In addition to video, data collected from other sensors measure ambient light, fluorescence (a measure of phytoplankton), optical backscatter (an index of turbidity), CTD (for salinity, temperature, and depth), flow rate (speed of VPR), and the alititude of the VPR off the bottom. The new VPR has now been towed for thousands of miles through the ocean, including a transAtlantic crossing on the research vessel Knorr.
-By Cabell Davis