Using 180 degrees field-of-view imaging polarimetry, we measured the reflection-polarization patterns of two artificial surfaces (water-dummies) in the red, green and blue spectral ranges under clear and partly cloudy skies at different solar elevations. The dummies consisted of a horizontal glass pane with a matt black or matt light grey cloth underneath, imitating a dark or bright water body,...

Four methods have been used for the estimation of total cloud amount and low clouds: visual observations, Long method applied on pyranometer measurements, Automatic Partial Cloud Amount Detection Algorithm (APCADA) pyrgeometers ceilometer measurements base height. Records from meteorological observers indicate that clear days (0–1 octa) represent most frequent clouds. In contrast, is more aleat...