Résumé :
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Detailed studies of light in forest canopies typically require a large number of light sensors. However, the high cost of commercially available sensors can make such studies very expensive. This report describes the construction and testing of a practical, rugged, and inexpensive sensor for measuring photo-synthetic photon flux density. Detailed instructions are provided for assembly and calibration. The sensor was made from a gallium arsenide phosphide (GaAsP) photodiode held within a protective casing of acrylic and aluminium. The LI-190 Quantum Sensor (LI-COR Inc.) was used as a standard for comparison. The stability of the GaAsP sensor compared favourably with the LI-190 during a 24-month open-sky test. Results from nine GaAsP sensors exhibited signal drift of 3 - 23%, and from four LI-190 quantum sensors of 5 - 18.5%. The GaAsP sensors generally drifted by
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