https://cdn.earthdata.nasa.gov/conduit/upload/5182/KeywordsCommunityGuide_Baseline_v1_SIGNED_FINAL.pdf 23.8 2026-04-29T10:52:37.449Z https://gcmd.earthdata.nasa.gov/KeywordViewer/scheme/instruments/a5475980-7a92-4664-8114-087141d2b7ce OPC The Optical Plankton Counter (OPC) is an operational instrument that detects, sizes, and counts individual particles based on measuring the attenuance, or diminution in intensity, of a collimated light beam intercepted by transiting particles. The OPC can determine the size of individual particles with effective diameters in the range 250 µm-2 cm. Thus, nearly the full size spectrum of mesozooplankton can be registered, as well as euphausiids, fish eggs, other small organisms, marine snow, and seston, or small particulate matter in suspension. The nature of the particles being sensed and quantified must be determined by physical capture, a process that is sometimes referred to as calibration. Particle concentrations as high as 10,000 particles per cubic meter can be resolved for counting purposes. The OPC is often towed, at speeds up to 8 knots, but it can also be attached to moorings and other platforms, and may be used in the laboratory. Its ordinary depth rating is 1000 m, but that of a special model is 4000 m.Information obtained from http://www.usm.maine.edu/gulfofmaine-census/Group: Instrument_Details Entry_ID: OPC Group: Instrument_Identification Instrument_Category: In Situ/Laboratory Instruments Instrument_Class: Photon/Optical Detectors Short_Name: OPC Long_Name: Optical Plankton Counter End_Group Online_Resource: http://research.usm.maine.edu/gulfofmaine-census/research/research-technology/optical-instruments-and-methods-for-remote-sensing/optical-plankton-counter-opc/ Sample_Image: http://research.usm.maine.edu/gulfofmaine-census/wp-content/images/Technology/OPCImage01b.jpg Creation_Date: 2008-07-18End_Group