LI-COR LI-192 User manual

Measuring PPFD and PPFFR
With LI-COR Underwater Radiation Sensors
LI-COR Technical Solutions
Phytoplankton, algae, and aquatic plants use photosynthetically
active radiation (PAR) with wavelengths between 400 and 700
nanometers for photosynthesis. This radiation comes from the
sun and its intensity is characterized as Photosynthetic Photon
Flux Density (PPFD) in units of micromoles of photons per
square meter per second (μmol/m2/s). These organisms are also
illuminated by reflections from the bottom surface and particles
suspended in the water. The total number of photons incident
on a point from all directions is called Photosynthetic Photon
Flux Fluence Rate (PPFFR), also in units of μmol/m2/s.
These underwater organisms can use direct and reflected light
equally efficiently for photosynthesis, and for this reason,
scientists may want to measure both the downwelling PPFD as
well as the PPFFR. This measurement can be performed with an
LI-192 Underwater Quantum Sensor for downwelling PPFD and
an LI-193 Spherical Quantum Sensor for PPFFR. Both of these
sensors should face upward towards the sun when deployed in an
ocean, a lake, or a stream.
The 2009S Lowering Frame was designed to hold one upward-
facing and one downward-facing sensor. However, with a few
modifications and parts, you can mount two upward-facing
sensors to the frame. You will need to purchase three 6-32
standoffs (2 inches long, part number 170-00184) and three 6-32
headless screws (3/4 inches long, part number 142-05469). In
addition, you will need the three shrink-wrapped screws from
the 9901-220 Underwater Parts Kit that comes with each sensor.
1. Thread the headless screws into the base of the LI-193
Spherical Quantum Sensor. Make sure they are hand tight.
2. Thread the standoffs onto the screws. Make sure they are
hand tight as well.
3. Connect the 2222UWB Underwater Cable to the sensor.
Make sure to insert it through the 2009S Lowering Frame’s
lower ring first. Align the yellow dot on the base of the
sensor with the raised nub on the cable. Take care not to
bend or twist the pins—they are more fragile than they
appear and may break if not properly connected. Then press
the cable onto the sensor until there is an audible ‘pop’ as it
snaps into place.
4. Slide the white collar onto the sensor connector and thread
until hand tight. Some pressure may need to be applied, as
the standoffs rub against the collar.
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5. Insert the shrink-wrapped screws from the Underwater
Parts Kit through the ring of the lowering frame and thread
them into the standoffs. This will require a small flathead
screwdriver.
Once this sensor has been mounted to the lowering frame, insert
the LI-192 Underwater Quantum Sensor into the other ring.
Connect the cable before inserting the shrink-wrapped screws to
ensure that the yellow dot and the raised nub align. Use the cable
ties from the Underwater Parts Kit to attach both underwater
cables to the frame, ensuring that there is enough slack in the
cable to prevent strain. Attach a rope or lowering cable to the
ring at the top of the frame. The two sensors should now be
roughly the same height and ready for measurements.