CHAPTER 4
CALIBRATION
6
4
Calibration
4.1
Calibration Procedure
US-SQS sensors are calibrated using a LI-COR working standard
calibration lamp. The LI-COR standard lamp has been calibrated
against a reference standard lamp traceable to the National Institute of
Standards and Technology USA (NIST). The lamp is a 200 W tung-
sten halogen lamp operated at a color temperature of 3150° Kelvin.
The lamp is mounted in a LI-COR optical radiation calibrator Model
1800-02. Calibration accuracy of the optical radiation calibrator is ± 4
% from 350-1000 nm.
Spectral sensitivity is calibrated using a Bentham TMc300F
Monochromator system and a reference diode. The reference diode is
calibrated against a standard diode traceable to the NIST. Accuracy
from 380 - 900 nm is ± 5 %.
The calibration constant given in the calibration sheet, takes into
account the spectral difference between the calibration lamp and natu-
ral sun light. The spectrum used for natural sun light is ASTM G-173-
03-global tilt (ISO 9845-1, 1992). As a result the reading for the
PPFR value is most accurate in natural sun light.
4.2
Calibration Certificate
Every US-SQS is accompanied by a certificate. Figure 4 shows a
typical certificate of calibration.
The Calibration Multiplier given in the certificate is the value that
needs to be entered into the ULM-500 for the direct reading of PPFR
values in calibrated units: µmol m
-2
s
-1
.
There are two Calibration Multipliers given, one for the usage in
air, the other for the usage in water.
