Lunar Photometric

The Lunar Photometer research group, established in 2011 between Cimel Electronique and the IARC, is focused on the design and implementation of new strategies to tackle the problems to monitor atmospheric aerosols and water vapor content at night. The most important obstacles to overcome are the low incoming energy from the Moon, the variation of the Moon’s illumination inherent to the lunar cycle, as well as the non-lambertian reflectance properties of this celestial body.

In this regard, the Lunar-Langley Method (Barreto et al., 2013) has emerged as a useful tool to perform an accurate calibration of lunar photometers, and the CE318-U prototype was developed as an instrument capable to obtain aerosol optical depth (AOD) and precipitable water vapor (PWV) with similar accuracy to daytime measurements. Further efforts led to the development of the first sun-sky-lunar photometer (trade name CE318-T) in 2014. This new instrument is able to perform daytime and nighttime photometric measurements using both the Sun and the Moon as light source, allowing the extraction of a complete diurnal cycle of aerosol properities and water vapor content, valuable to enhance atmospheric monitoring.

IARC CE318-T observations started in 2014, with three prototypes installed at IZO: one reference instrument and two secondaries. The reference, assumed as CE318-T master, is currently working as IZO master. The two CE318-T secondaries were used to develop and check new procedures to transfer the absolute Lunar Langley calibration technique to field instruments. The information extracted from these three years of CE318-T observations has allowed the comprehensive assessment of the CE318-T performance, and in addition, has served to identify other sources of problems related to lunar photometry.

As a result of this analysis, the AERONET team accepted this new Cimel version henceforth in AERONET, once the homogeneity of the network was ensured, suggesting the replacement of CE318-N instruments by the new CE318-T as far as possible (see the news published on 2 Oct. 2016, on the AERONET webpage).