Aerosol Optical Thickness (AOT) mapping of Islamabad region using indigenously fabricated, locally-calibrated, economical sunphotometer and GLOBE sunphotometer

摘要

This study aims at ground based atmosphere monitoring for Islamabad region (33.7167°N and 73.667°E,508 m altitude) using locally designed dual channels, (Green (550nm) and red (625nm)) LED based handheldsunphotometer. Calibration was done by using improvised transfer of calibration method employingpre-calibrated GLOBE (Global Learning and Observation to Benefit Environment) sunphotometer.Aerosol optical thickness (AOT) of said region for the month of July, August 2017 was calculated usingacquired data for red and green channels. Matching trends (correlation up to 95%) were observed forAOT obtained with GLOBE and local sunphotometer. AOT of Islamabad region generated by satellitebasedModerate Resolution Imaging Spectro-radiometer (MODIS) instrument board on AQUA and Terrasatellites has also been presented for calibration period (Oct 2016-Feb 2017) to qualify our findings. Theinter-comparison of data with MODIS instrument AQUA and Terra from Oct 2016 to Feb. 2017 with thelocal sunphotometer green channel yielded a correlation coefficients in range of 0.51-0.55 approachingthe previously reported range values of (～0.55-0.60) for similar comparison. Along with AOT, in thisstudy, the average daily Angstrom exponent α, and angstrom turbidity constant ??, have also beenreported. The average of angstrom exponent for recorded data is 1.42, this implies moderately pollutedurban atmosphere of area under study, while the 19th and 20th July are clearest day for monitoring periodwith ?? = 0.07 and ?? = 0.083 respectively.