Comparison of AOD products of Prede, PFR and Cimel photometers on a 12 years dataset at Meteorological Observatory Lindenberg

Photometers are the most accurate instruments to retrieve the aerosol optical depth (AOD) for a given spectral channel (e.g. 500 nm). There are three main networks of photometers: GAW-PFR (Global Atmosphere Watch - Precision Filter Radiometer) using the instrument PFR (Precision Spectral radiometer), AERONET (AErosol RObotic NETwork): AOD and aerosol properties measurements network using Cimel CE-318 photometer, and SKYNET (SKY Measurements NETwork), using the instrument Prede POM (Precise design Of Meteorological). These three networks use different instruments, different measurement methods, different calibration methods and different retrieval methods algorithms).

The Meteorological observatory Lindenberg (MOL-RAO) from German meteorological service (Deutscher Wetterdienst: DWD) in Lindenberg (Tauche, Germany) is the only site worldwide operating permanently the three instruments of these three networks. There is a dataset of 12 years (since 2013) of collocated and synchronized AOD measurements of GAW-PFR, AERONET, SKYNET photometry networks at this station.

In this study, we quantify the differences in the AOD from the products of these three different networks, we investigate the sources of these differences, computing the corrections on the optical depth (Rayleigh, ozone, NO2), showing the air mass dependences and analysing which differences are artificial (different way of computing with different inputs or equations during the retrievals) or inherent to the measurement itself (instrumental difference, calibration issues). Also, we select a large set of “golden days”, these are measurements days for which we are sure, that cloud flagging do not impact the comparison (purely sunny days) and for which we know (log books of the station) that there were no hardware instrumental issue.