Gulf of Maine Area Program

Illustration of the Laser-Optical Plankton Counter (LOPC). Credit: ©Alex Herman, Bedford Insitute of Oceanography. Click to enlarge

Laser-Optical Plankton Counter (LOPC)

The Laser-Optical Plankton Counter (LOPC) is an optical plankton counter with an imaging capability. Particles passing through a collimated laser light beam block the light falling on an array of sensors oriented perpendicularly to the flow direction, thus allowing outlines of exposed particles to be registered. Cross-sectional shapes in the range 1.5-35 mm can be resolved, enabling automated classification algorithms to be applied. Particles as small as 100 µm can be detected, sized, and counted. Concentration densities as high as 1,000,000 particles per cubic meter can be quantified.

llustration of the Laser-Optical Plankton Counter (LOPC) mounted in the Moving Vessel Profiler (MVP) Multi-Sensor Free-Fall Fish. Credit: ©Alex Herman, Bedford Insitute of Oceanography. Click to enlarge

Like its predecessor, the Optical Plankton Counter (OPC), the LOPC can be towed, at speeds up to 15 knots, or otherwise deployed from a wide range of platforms, including, for example, moorings, nets, remotely-operated vehicles (ROVs), various towbodies, and vertical profilers. The LOPC fits easily into the Moving Vessel Profiler (MVP) Multi-Sensor Free-Fall Fish (MSFFF), a towed vehicle designed to house multiple external sensors. This type of configuration allows integration of the plankton data stream with various time-based data plots, such as conductivity, temperature, depth and flow speed. The current depth rating of the LOPC is 660 m, but two future models will have respective depth ratings of 3400 and 6000 m.

Shape profiles obtained from an LOPC mounted on a Batfish vehicle towed at 8 knots. Silhouettes show profiles of euphausiids and copepods of a variety of sizes. Credit: ©Alex Herman, Bedford Institute of Oceanography. Click to enlarge

Data collected from the LOPC installed on an MVP 200 Multi-Sensor Free-Fall Fish, along with an Applied Microsystems Limited CTD. Left, LOPC Interface Software display of binned counts versis digital size units or ESD (equivalent spherical diameter). Right, a continuous display of images of Multi-Element Plankton (MEP). Credit: ©Alex Herman, Bedford Insitute of Oceanography. Click to enlarge

Related Links

Alex Herman, OPC application note:
http://www.alexherman.com/recent_paper_001.php
Brooke Ocean Technology, Ltd:
http://www.brooke-ocean.com/lopc.html

References
Herman, A.W, B. Beanlands, M. Chin-Yee, A. Furlong, J. Snow, S. Young, T. Phillips. 1998. The Moving Vessel Profiler (MVP): in-situ sampling of plankton and physical parameters at 12 kts and integration of a new laser/optical plankton counter. Oceanology 98, 102: 123-135.
 
Herman, A.W. 2001. A review of OPC and an introduction to the next generation of OPC: The Laser OPC. An International Global Oceans Ecosystem Dynamics (GLOBEC) Program Report of the Optical Plankton Counter Workshop. Tromso, Norway, 17-20 June 2001, pp 3-6. http://www.pml.ac.uk/globec/Publications/Reports/GlobecReport17Text.pdf