Abstract
Japan Meteorological Agency (JMA) continuously monitors the aerosol optical depth (AOD) at three stations in Japan. Until the year 2006 sunphotometers (Model MS110, manufactured by EKO Instruments, Japan) had been used to measure AOD. Since the year 2007 precision filter radiometers(PFR, available from Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center, PMOD/WRC) has been used to monitor AOD following recommendations by World Meteorological Organization (WMO). WMO encourages that the calibration constant over an interval of one year and the uncertainty of measured AOD are less than 2% and 0.02, respectively. In order to verify that WMO’s recommendations are being satisfied our sunphotometers were calibrated by Langley method. For the same purpose our PFR instruments are sent to PMOD/WRC periodically to determine the extraterrestrial calibration constants of each PFR instruments.
