CCD fiber optic spectrometer for the measurement of spectral irradiance

摘要

Recent technological advancements have made CCD spectrometers an increasingly suitable alternative to traditional monochromator-based instrumentation. The authors have developed instrumentation for the near instantaneous measurement of spectral global, direct, diffuse, reflected and southward-tilted irradiances. The system uses an AvaSpec2048TEC-2 - a dual channel thermo-electric-cooled fiber optic spectrometer from Avantes Inc. Each channel has a 2048-pixel linear array detector and the system achieves a spectral resolution of 0.0007 urn (FWHM) over the range 0.241-1.1 urn. The system also includes sensor heads, fiber optic cables and a multiplexer. Two types of sensor heads have been developed: a pyrheliometer configuration for direct beam, and a pyranometer configuration for global, diffuse, reflected and tilted measurements. Calibration uses a system of standard light sources. Cosine errors inherent to the spectralon diffusers have been characterized and corrections are applied to data from each sensor head. Accuracy of global irradiance is examined by comparing measurements against global photosynthetically active radiation (PAR) (0.395 - 0.695 urn) from Eppley red and green dome pyranometers. PAR daily totals (MJ/m2/day) and one minute averages (W/m2) are compared for 35 days in 2009 and daily totals are within ± 10% from June to October.