Apogee SQ-225 Gebruikershandleiding - Pagina 14
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Spectral Errors for PPFD and YPFD Measurements with Apogee SQ Series Quantum Sensors
Radiation Source (Error Calculated Relative to Sun, Clear Sky)
Sun (Clear Sky)
Sun (Cloudy Sky)
Reflected from Grass Canopy
Reflected from Deciduous Canopy
Reflected from Conifer Canopy
Transmitted below Grass Canopy
Transmitted below Deciduous Canopy
Transmitted below Conifer Canopy
Radiation Source (Error Calculated Relative to Cool White Fluorescent, T5)
Cool White Fluorescent (T5)
Cool White Fluorescent (T8)
Cool White Fluorescent (T12)
Compact Fluorescent
Metal Halide
Ceramic Metal Halide
High Pressure Sodium
Blue LED (448 nm peak, 20 nm full-width half-maximum)
Green LED (524 nm peak, 30 nm full-width half-maximum)
Red LED (635 nm peak, 20 nm full-width half-maximum)
Red, Blue LED Mixture (85 % Red, 15 % Blue)
Red, Green, Blue LED Mixture (72 % Red, 16 % Green, 12 % Blue)
Cool White Fluorescent LED
Neutral White Fluorescent LED
Warm White Fluorescent LED
Quantum sensors can be a very practical means of measuring PPFD and YPFD from multiple radiation sources, but spectral
errors must be considered. The spectral errors in the table above can be used as correction factors for individual radiation
sources.
Underwater Measurements and Immersion Effect
When a quantum sensor that was calibrated in air is used to make underwater measurements, the sensor reads low. This
phenomenon is called the immersion effect and happens because the refractive index of water (1.33) is greater than air
(1.00). The higher refractive index of water causes more light to be backscattered (or reflected) out of the sensor in water
than in air (Smith,1969; Tyler and Smith,1970). As more light is reflected, less light is transmitted through the diffuser to the
detector, which causes the sensor to read low. Without correcting for this effect, underwater measurements are only relative,
which makes it difficult to compare light in different environments.
The SQ-200 series sensors have an immersion effect correction factor of 1.08. This correction factor should be multiplied to
measurements made underwater.
Further information on underwater measurements and the immersion effect can be found
at http://www.apogeeinstruments.com/underwater-par-measurements/.
PPFD Error [%]
YPFD Error [%]
0.0
0.0
1.4
1.6
5.7
-6.3
4.9
-7.0
5.5
-6.8
6.4
-4.5
6.8
-5.4
5.3
2.6
0.0
0.0
-0.3
-1.2
-1.4
-2.0
-0.5
-5.3
-3.7
-3.7
-6.0
-6.4
0.8
-7.2
-12.7
8.0
8.0
26.2
4.8
-6.2
2.4
-4.4
3.4
0.2
-4.6
-0.6
-6.7
-5.2
-10.9
-13.0
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