Underwater PAR Measurement
Accurate measurement of Photosynthetically Active Radiation (PAR, 400-700 nm) in aquatic environments is accomplished using either the LI-192 Underwater Quantum Sensor or the LI-193 Spherical Quantum Sensor. Limnologists, oceanographers and biologists conducting aquatic productivity studies and vertical profiling have used these sensors extensively.
For extremely turbid conditions, radiation levels with resolution to 0.01 µmol s-1 m-2 can be measured with the LI-192 or LI-193 quantum sensors and the LI-1400 DataLogger. Both the LI-192 and the LI-193 use computer-tailored filter glass to achieve the desired quantum response. Calibration is traceable to NIST.
LI-192
Underwater or atmospheric Photosynthetic Photon Flux Density (PPFD) can be accurately measured using the LI-192 Underwater Quantum Sensor. The LI-192 is cosine corrected and features corrosion resistant, rugged construction for use in freshwater or saltwater and pressures up to 800 psi (5500 kPa, 560 meters depth).
LI-193
The LI-193 Underwater Spherical Quantum Sensor gives an added dimension to underwater PAR measurements as it measures photon flux from all directions. This measurement is referred to as Photosynthetic Photon Flux Fluence Rate (PPFFR) or Quantum Scalar Irradiance. This is important, for example, when studying phytoplankton, which utilize radiation from all directions for photosynthesis.
The LI-193 features a high sensitivity optical design and compact, rugged construction (3400 kPa, 350 meters depth, 3400 kPa = 493 psi).
The graph to the left indicates the typical angular response of the LI-193 Spherical Quantum Sensor. The low response on the bottom of the sensor is due to light blockage by the detector housing. The error due to this low response is not significant in most cases because of the small portion of upwelling radiation compared to the total radiation.