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

Abstract

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 (u D AOD ) for Langley-calibrated instruments similar to the expected values for other reference instruments (0.002-0.009). We have also found u D AOD 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 (u N AOD ) 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 suncalibrated using the Langley technique, we found u N AOD 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 starphotometer-collocated measurements and also by means of a day/night coherence transition test using the CE318-T masPublished by Copernicus Publications on behalf of the European Geosciences Union. Á. Barreto et al.: The new sun-sky-lunar Cimel CE318-T multiband photometerter 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 u N AOD value...

Assessment of nocturnal aerosol optical depth from lunar photometry at the Izaña high mountain observatory

“…Recently, Barreto et al (2016) presented the new photometer CE318-T which combines the features of the extensively used CE318 Cimel Sun photometer standard model in the AERONET network, with the lunar photometer prototype previously presented in Barreto et al (2013a, b). The higher precision of this new instrument compared to the previous versions of Sun and Moon photometers and its ability to monitor atmospheric aerosols in a diurnal cycle have made it a suitable instrument to replace the CE318-AERONET reference instrument.…”

“…However, infrastructure and logistic constraints still represent an important limitation for the operational use of stellar measurements, especially for global networks such as AERONET. Alternatively, Moon photometry is a technique that can be implemented more easily, and at a lower cost, in an operational way (Barreto et al, 2016). Nevertheless, the Moon photometry technique is still affected by notable limitations.…”

“…As many authors have stated (Berkoff et al, 2011;Barreto et al, 2013aBarreto et al, , b, 2016), a precise Moon irradiance model is mandatory in Moon photometry to take the continuous change of the Moon's brightness over the cycle into account. In this respect, the Robotic Lunar Observatory (ROLO) model, developed by Kieffer and Stone (2005), is the most careful radiometric study on the Moon's brightness to date (Cramer et al, 2013).…”

“…In this respect, the Robotic Lunar Observatory (ROLO) model, developed by Kieffer and Stone (2005), is the most careful radiometric study on the Moon's brightness to date (Cramer et al, 2013). The ROLO model has recently emerged as a unique tool for Moon photometry (Berkoff et al, 2011;Barreto et al, 2013aBarreto et al, , b, 2016 and is an essential part of the calibration process. Although this model provides precise information about the change of the Moon's irradiance with the phase angle (g) and lunar librations, small systematic effects have been found in this model.…”

“…Cramer et al (2013) developed a novel apparatus to accurately measure the lunar spectral irradiance with the aim of estimating these systematic effects in the ROLO model. Barreto et al (2016) used the CE318-T and the ROLO model to retrieve AOD at day-and nighttime at Izaña, a high altitude observatory located at Tenerife (the Canary Islands, Spain). These authors observed an important dependence of the AOD uncertainty with phase angle and also a faint nocturnal cycle in AOD, indicating a possible dependence of AOD uncertainty on the Moon's zenith (θ) and phase angles.…”