WMO-CIMO Testbed

Color Sky Quality Meter (CoSQM) 

Four novel multispectral Color Sky Quality Meter (CoSQM) photometers were installed in April 2019 in four different locations in Tenerife differently affected by their proximity to the lighting sources and elevation: Santa Cruz de Tenerife, Izaña (Figure 1), IAC Observatory and Teide Peak . This deployment is considered a first step toward a worldwide CoSQM network, with Tenerife as an important site for atmospheric sensing science thanks to the IARC-AEMET facilities which can be considered reference in terms of aerosol detection and cross calibration capabilities. This cheap and open-source instrument is able to sample the multispectral properties of the artificial light scattered by the atmosphere. These night sky brightness measurements will be used to partly fill the gaps in the spatio-temporal AOD dataset.


Figure 1.- CoSQM instrument deployed at Izaña Observatory. Photo Credit: Martin Aube

A new methodology will be developed in an ongoing publication that links together the zenith artificial night sky brightness and the AOD. Such method is especially suitable to be applied to moonless nights and to light polluted sites.

This deployment is considered a first step toward a worldwide CoSQM network. Marseille et al. (2021) presented an innovative method for estimating the aerosol optical depth using an empirical relationship between Zenith Night Sky Brightness (ZNSB) measured at night with the CoSQM and AOD retrieved at daytime from the AErosol Robotic NETwork (Holben et al., 1998; Giles et al., 2019). The empirical relationship is especially suited to light-polluted regions with light pollution sources located within a few kilometres of the observation site. This is the case of Santa Cruz de Tenerife. A coherent day-to-night aerosol optical depth and Ångström Exponent evolution in a set of 354 days and nights from August 2019 to February 2021 was used to verify the suitability of this new methodology (Figure 1), including an estimation of the method uncertainty, set at 0.02 for AOD and 0.75 for AE.

Figure 1.- Continuity of (a) AOD and (b) Angstrom Exponent (AE) derived by means of COSQM ZNSB compared to AERONET daytime sun photometer measurements during and after a calima event. AERONET AE values were retrieved with 440–675 nm daytime sun photometer measurements. Reprinted from Marseille et al. (2021).

Publications:

  • Holben, B.N.; Eck, T.; Slutsker, I.; Tanre, D.; Buis, J.; Setzer, A.; Vermote, E.; Reagan, J.; Kaufman, Y.; Nakajima, T.; et al. AERONET—A federated instrument network and data archive for aerosol characterization. Remote Sens. Environ., 66, 1–16, 1998.