On 1-17 June 2017 (Figure 1), a Lunar Photometric Campaign was hosted at the Izaña Atmospheric Observatory. In addition, on 7-8 June 2017 (Figure 2), a workshop on the same theme was held at IZO. These events were organized by the Izaña Atmospheric Research Center and the Atmospheric Optics Group of Valladolid University in the framework of the WMO-CIMO Testbed for Aerosols and Water Vapour Remote Sensing Instruments.

Figure 1.- Instruments taking measurements of the moon during the 2017 lunar photometric field campaign (left: the Cimel CE318-T and right: the stellar photometers).

The importance of the atmospheric aerosol effect on the climate has been known by the scientific community for several decades. However, the main ground-based methodology used to characterize the atmospheric aerosol, solar photometry, is not able to provide information at night or for long periods in polar areas and in high latitude stations. This lack of information reduces the ability of scientists to study the diurnal dynamics and evolution of atmospheric aerosols and other atmospheric features at high latitudes such as the Arctic haze. The incorporation of nocturnal information to the current aerosol ground-based monitoring networks would add important information to the aerosol transport models, either by assimilation or validation studies, in addition to the validation of satellite products.

Figure 2.- Participants of the lunar photometry workshop, Izaña, 7-8 June 2017.

The objective of this campaign was to intercompare the instruments and procedures currently being used to determine the aerosol optical thickness at night. This campaign involved the participation of several groups: IARC, GOA-UVA, Photons (University of Lille, France), the World Radiation Center (PMOD/WRC) in Davos (Switzerland), the Institute of Atmospheric Sciences and Climate of Italy, the French company CIMEL electronique (manufacturer of the CE318T photometers used in the AERONET network), the company SIELTEC Canarias, (manufacturer of the SONA All Sky camera), the Meteorological State Service of Germany, the Atmospheric Physics Group of the University of Granada and the Astrophysics Institute of the Canary Islands. The last two groups participated with instruments that use stars instead of the Moon to determine the aerosol optical thickness. The IARC also has a micro-pulsed Lidar capable of providing aerosol information at night.

During the Workshop, the most appropriate methodologies to obtain optimal results with the lunar photometers were discussed. This meeting facilitated the exchange of ideas and experiences between participants in order to promote the research in this area. Groups from the United States Geological Survey, the NASA AERONET group, the University of Sherbrooke of Canada, the Institute of Physics of the Czech Academy of Sciences and the Finnish Meteorological Institute also participated in the Workshop.