Analysis differences between the three main aerosol photometry networks in AOD retrieval methods

Trainer: Lionel Doppler

Introduction: There are three main aerosol photometry networks. These are AERONET (AErosol RObotic NETwork,
using the Cimel CE318 instruments), SKYNET (SKY Measurements NETwork, using Prede-POM instruments) and
GAW-PFR (Global Atmosphere Watch – Precision Filter Radiometer network, using the instruments PFR). These
networks use not only different instrumentation, but also different retrieval methods. These different approaches
of retrievals lead to artificial differences in the final AOD (Aerosol Optical Depth) products delivered by the three
networks. It is one objective of the COST Action HARMONIA to find a harmonized method to retrieve the AOD, that
suits to the stations of all three networks.
Idea: The idea is to find out and point out the differences in the retrieval methods and to evaluate the consequences
on the final AOD products between the three main networks. We will consider the dataset of station “observatory
Lindenberg”: DWD, MOL-RAO (Deutscher Wetterdienst, Metorologisches Observatorium Lindenberg) in Lindenberg
(Tauche, Germany), since all three instruments and networks are present at this station. We first show the
differences in the AOD final product of the three different networks. In a second step we will investigate what are
the differences in retrieval procedures: Airmass computation, Rayleigh Optical Depth computation, AOD corrections
of gas absorption (Ozone, NO2) and we will find a common way to reprocess the data in order to avoid these artificial
differences in the final products.

1. Get the AOD dataset of some given days for the station “observatory Lindenberg” for all three instruments-
networks couples: Cimel-AERONET, PFR-GAW, Prede-SKYNET.

2. Find out the common wavelengths for the three networks’ products, and make daily plots of AOD for all three
networks for each common wavelength in order to visualize the differences. Make an analysis of these graphics.
3. Investigate in the dataset with help of publications and documentation (papers, reports) how the following
processes are treated in the different networks: Air-mass, Rayleigh optical depth, absorption of ozone,
absorption of NO2. Make a tabulation report.
4. Define a strategy to optimize the treatment of these processes, considering the other measurements of the
station “observatory Lindenberg” (supersite for atmospheric and meteorological measurements), for
instance atmospheric pressure ad ozone total column (TOC).
5. Reprocess the data of all three networks using the here above defined strategy of processing and analyze
the improvements regarding the differences between the products of the instruments of the three
6. (If time) extend the study to one or several years (up to ten years data available) of data at the station
“observatory Lindenberg”.

Goal:Understanding the retrieval processes of AOD retrieval for all three main networks (AERONET, SKYNET, GAW-
PFR), propose a harmonized retrieval strategy to get rid of artificial differences in the final AOD products. Present the results for the dataset of the station “observatory Lindenberg” (DWD, MOLRAO). Depending on the results and on the possibility to join the conference, an abstract can be submitted to the EMS2024 Harmonia session and, depending on the results, a paper can be submitted to a peer reviewed journal.