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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 2 | Copyright
Atmos. Meas. Tech., 9, 631-654, 2016
https://doi.org/10.5194/amt-9-631-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 24 Feb 2016

Research article | 24 Feb 2016

The new sun-sky-lunar Cimel CE318-T multiband photometer – a comprehensive performance evaluation

África Barreto1,2, Emilio Cuevas1, María-José Granados-Muñoz3,4, Lucas Alados-Arboledas3,4, Pedro M. Romero1, Julian Gröbner5, Natalia Kouremeti5, Antonio F. Almansa1,2, Tom Stone6, Carlos Toledano7, Roberto Román7, Mikhail Sorokin8, Brent Holben8, Marius Canini2, and Margarita Yela9 África Barreto et al.
  • 1Izaña Atmospheric Research Center, Meteorological State Agency of Spain (AEMET), Spain
  • 2Cimel Electronique, Paris, France
  • 3Department of Applied Physics, University of Granada, Granada, Spain
  • 4Andalusian Institute for Earth System Research, IISTA-CEAMA, University of Granada, Junta de Andalucía, Granada, Spain
  • 5Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center (PMOD/WRC), Davos, Switzerland
  • 6US Geological Survey, Flagstaff, USA
  • 7Grupo de Óptica Atmosférica, Universidad de Valladolid, Valladolid, Spain
  • 8NASA/Goddard Space Flight Center, Greenbelt, USA
  • 9Instrumentation and Atmospheric Research Department, National Institute for Aerospace Technology (INTA), Madrid, Spain

Abstract. This paper presents the new photometer CE318-T, able to perform daytime and night-time photometric measurements using the sun and the moon as light source. Therefore, this new device permits a complete cycle of diurnal aerosol and water vapour measurements valuable to enhance atmospheric monitoring to be extracted. In this study we have found significantly higher precision of triplets when comparing the CE318-T master instrument and the Cimel AErosol RObotic NETwork (AERONET) master (CE318-AERONET) triplets as a result of the new CE318-T tracking system. Regarding the instrument calibration, two new methodologies to transfer the calibration from a reference instrument using only daytime measurements (Sun Ratio and Sun-Moon gain factor techniques) are presented and discussed. These methods allow the reduction of the previous complexities inherent to nocturnal calibration. A quantitative estimation of CE318-T AOD uncertainty by means of error propagation theory during daytime revealed AOD uncertainties (uDAOD) for Langley-calibrated instruments similar to the expected values for other reference instruments (0.002–0.009). We have also found uDAOD values similar to the values reported in sun photometry for field instruments ( ∼ 0.015). In the case of the night-time period, the CE318-T-estimated standard combined uncertainty (uNAOD) is dependent not only on the calibration technique but also on illumination conditions and the instrumental noise. These values range from 0.011–0.018 for Lunar Langley-calibrated instruments to 0.012–0.021 for instruments calibrated using the Sun Ratio technique. In the case of moon-calibrated instruments using the Sun-Moon gain factor method and sun-calibrated using the Langley technique, we found uNAOD ranging from 0.016 to 0.017 (up to 0.019 in 440 nm channel), not dependent on any lunar irradiance model.
A subsequent performance evaluation including CE318-T and collocated measurements from independent reference instruments has served to assess the CE318-T performance as well as to confirm its estimated uncertainty. Daytime AOD evaluation, performed at Izaña station from March to June 2014, encompassed measurements from a reference CE318-T, a CE318-AERONET master instrument, a Precision Filter Radiometer (PFR) and a Precision Spectroradiometer (PSR) prototype, reporting low AOD discrepancies between the four instruments (up to 0.006). The nocturnal AOD evaluation was performed using CE318-T- and star-photometer-collocated measurements and also by means of a day/night coherence transition test using the CE318-T master instrument and the CE318 daytime data from the CE318-AERONET master instrument. Results showed low discrepancies with the star photometer at 870 and 500 nm channels ( ≤ 0.013) and differences with AERONET daytime data (1 h after and before sunset and sunrise) in agreement with the estimated uNAOD values at all illumination conditions in the case of channels within the visible spectral range, and only for high moon's illumination conditions in the case of near-infrared channels.
Precipitable water vapour (PWV) validation showed a good agreement between CE318-T and Global Navigation Satellite System (GNSS) PWV values for all illumination conditions, within the expected precision for sun photometry.
Finally, two case studies have been included to highlight the ability of the new CE318-T to capture the diurnal cycle of aerosols and water vapour as well as short-term atmospheric variations, critical for climate studies.

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This paper presents the new photometer CE318-T, able to perform daytime and night-time photometric measurements using the sun and the moon as light sources. This new device permits a complete cycle of diurnal aerosol and water vapour measurements to be extracted, valuable to enhance atmospheric monitoring. We have also highlighted the ability of this new device to capture short-term atmospheric variations, critical for climate studies.
This paper presents the new photometer CE318-T, able to perform daytime and night-time...
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