Introducing a Cloud Screening Detector Using Global Horizontal Irradiances in UV and PAR in Thessaloniki, Greece
In Thessaloniki, Greece, a NILU-UV multi-filter radiometer has been in regular operation since 2005 providing photosynthetically active radiation and ultraviolet (UV) measurements at 1-min intervals. In this study, a new approach to detect cloud presence based on such measurements, is evaluated with reference to all sky camera images taken at 15 min intervals during the year 2014. Daily channel measurements sampled at 1-min intervals are analyzed using singular spectrum analysis (SSA) and provide daily trend cycle, periodic and noise components for each day of the study period. A set of statistical limitations and threshold criteria are then applied to the extracted SSA components in order to detect the presence of clouds via their attenuation effect. Cloud detections are cross-referenced against all sky images for a visual confirmation and overall assessment of the algorithm.
KeywordsPhotosynthetically Active Radiation Solar Irradiance Singular Spectrum Analysis Irradiance Measurement Global Horizontal Irradiance
The authors express their gratitude to Prof. C. Meleti for maintenance and calibration of the Kipp & Zonnen CM21 pyranometer operating in Thessaloniki, Greece.
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