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Solar and Photosynthetically Active Radiation

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PAR (umols/m^2/s) 0.0
Solar Radiation (W/m^2) 0.0
Last update: Sat Sep 23 02:10:01 2017 PDT

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Photosynthetically Active Radiation

Photosynthetically Active Radiation (PAR) refers to the energy in the 400 – 700 nm range of the electromagnetic spectrum. These are the wavelengths used by plants for photosynthesis. PAR levels affect plant growth and are of interest to biologists, and marine and terrestrial ecologists.

PAR is measured with a radiation sensor.

Solar Radiation (Light)

Solar radiation is the full spectrum of energy emitted by the sun and incident radiation on the Earth’s surface. We experience solar radiation as sunlight or daylight. Solar radiation is a key factor in the critical life process of photosynthesis. Solar radiation varies seasonally and diurnally and is an indicator for climate trending.

Solar radiation is measured with a pyranometer.

BML Pyranometer BML Solar Radiation

solar radiation sensorSolar Radiation

Instrument Type: LI-COR LI-200SA Pyranometer Sensor

Description: Silicon photodiode sensor calibrated to measure total radiation received from the sun; cosine-corrected to make the sensor insensitive to the direction of the radiation within the forward hemisphere

Location: Weather box, 2 m above ground, 40 m from coastal bluff
Latitude 38° 19' 01.52" N
Longitude 123° 04' 18.41" W

Installed: 5 February 2001

Specifications:
Sensitivity: 90 A/1000 W/m2
Accuracy: 5%
Response Time: 10 s

Acquisition Settings:
15 second running average
Mean value logged every 5 seconds
Data stored at 10 second intervals

PAR sensorPhotosynthetically Active Radiation

Instrument Type: LI-COR LI-190SA Quantum Sensor

Description: Silicon photodiode sensor filtered and calibrated to measure wavelengths of radiation effective in photosynthesis

Location: Weather box, 2 m above ground, 40 m from coastal bluff
Latitude 38° 19' 01.52" N
Longitude 123° 04' 18.41" W

Installed: 5 February 2001

Specifications:
Sensitivity: 8 A/1000 mols/s/m2
Accuracy: 5% Response Time: 10 s

Acquisition Settings:
Instantaneous:
15 second running average
Mean value logged every 5 seconds
Data stored at 10 second intervals

Integrated:
15 second running average
Integrated value calculated and logged hourly
Min/Max values and times logged hourly

Sensor Calibration and Quality Assurance Procedures

Photosynthetically Active Radiation/Pyranometer

Equipment:

Li-Cor LI-200SA Primary Pyranometer Sensor S/N PY47192
Li-Cor LI-200SA Secondary Pyranometer Sensor S/N PY30760
Li-Cor LI-1400 Secondary Data Logger S/N DLA 2289

Procedure: The secondary pyranometer is placed next to the primary pyranometer, so the two instruments receive similar amounts of radiation. The secondary data logger is programmed with the appropriate logging routine and channel multiplier for the secondary sensor. Data from both sensors are then acquired simultaneously for a period of one to two hours.


Sample Pyranometer Comparison

pyranometer comparison plot

Data from the two sensors are compared using Excel. After a graphical inspection, the values measured by the primary sensor are subtracted from the values measured by the secondary sensor, to determine the difference between the two. This difference value is then divided by the average of the two measured values, which results in a percentage.

If the difference between the values measured by the two sensors is within the manufacturer’s specifications of ± 5% for instrument accuracy, data from the primary sensor can be considered good.

Photosynthetically Active Radiation/Quantum Sensors

Equipment:

  • Li-Cor LI-190SA Primary Quantum Sensors S/N Q33278 & Q33279
  • Li-Cor LI-190SA Secondary Quantum Sensors S/N Q28666 & Q31059
  • Li-Cor LI-1400 Secondary Data Logger S/N DLA 2289

Procedure: The secondary quantum sensors are placed next to the primary quantum sensors, so the instruments receive similar amounts of radiation.  The secondary data logger is programmed with the appropriate logging routines and channel multipliers for the secondary sensors.  Data are then acquired with all sensors simultaneously for one to two hours. 

NOTE: Data for the integrated PAR sensor must be logged for a full hour after the hour in order to log a value.  (i.e. Logging started at 2:45 must continue until after 4:00.  The first point will be recorded at 4:00, not 3:00)

Sample Quantum Sensor Comparison:

light sensor qa chart

Data from the primary and secondary sensors are compared using Excel.  After a graphical inspection, the values measured by the primary sensor are subtracted from the values measured by the secondary sensor, to determine the difference between the two.  This difference value is then divided by the average of the two measured values, which results in a percentage. 

If the difference between the values measured by the two sensors is within the manufacturer’s specifications of ± 5% for instrument accuracy, data from the primary sensors can be considered good.