Dust-induced degradation of pyranometer sensitivity

The effect of dust accumulation on the sensitivity of pyranometers is studied in order to estimate the possible loss of accuracy associated with leaving the instruments unattended for extended periods of time. Under the arid conditions of Sede Boqer, Israel, the dust effect reduces the sensitivity of a horizontal pyranometer by one permille per day. For periods extending up to several weeks, the degradation rate appears to be constant, and no saturation effects are observed. The propagation of the measurement errors associated with dust accumulation on pyranometers to the errors on the beam and global radiation values derived from a stationary multipyranometer system is discussed.