Abstract
The study shows the first results of the column-integrated water vapor retrieved by the new ZEN-R52 radiometer. This new radiometer has been specifically designed to monitor aerosols and atmospheric water vapor with a high degree of autonomy and robustness in order to allow the expansion of the observations of these parameters to remote desert areas from ground-based platforms. The ZEN-R52 device shows substantial improvements compared to the previous ZEN-R41 prototype: a smaller field of view, an increased signal-to-noise ratio, better stray light rejection, and an additional channel (940 nm) for precipitable water vapor (PWV) retrieval. PWV is inferred from the ZEN-R52 Zenith Sky Radiance (ZSR) measurements using a lookup table (LUT) methodology. The improvement of the new ZEN-R52 in terms of ZSR was verified by means of a comparison with the ZEN-R41, and with the Aerosol Robotic Network (AERONET) Cimel CE318 (CE318-AERONET) at Izaña Observatory, a Global Atmosphere Watch (GAW) high mountain station (Tenerife, Canary Islands, Spain), over a 10-month period (August 2017 to June 2018). ZEN-R52 aerosol optical depth (AOD) was extracted by means of the ZEN–AOD–LUT method with an uncertainty of ±0.01 ± 0.13*AOD. ZEN-R52 PWV extracted using a new LUT technique was compared with quasi-simultaneous (±30 s) Fourier Transform Infrared (FTIR) spectrometer measurements as reference. A good agreement was found between the two instruments (PWV means a relative difference of 9.1% and an uncertainty of ±0.089 cm or ±0.036 + 0.061*PWV for PWV <1 cm). This comparison analysis was extended using two PWV datasets from the same CE318 reference instrument at Izaña Observatory: one obtained from AERONET (CE318-AERONET), and another one using a specific calibration of the 940-nm channel performed in this work at Izaña Atmospheric Research Center Observatory (CE318-IARC), which improves the PWV product.
Highlights
Water vapor induces a strong positive feedback in the climate system [1]
We studied the number of coincidences with the Aerosol Robotic Network (AERONET) cloud-screening quality control algorithm by matching the closest pairs of records (ZEN-R52 and CE318-AERONET) with a time difference within ±30 seconds
The results shown in this figure demonstrate that the ZEN Quality Control (ZEN-QC) filtering method is a suitable algorithm to screen instrumental errors and clouds, with an agreement of 68.8% with AERONET
Summary
Water vapor induces a strong positive feedback in the climate system [1]. It is the largest contributor to the natural greenhouse effect [2,3], has a key role in tropospheric dynamics and aerosol growth, and has a large temporal and spatial variability. Despite the fact that satellite remote sensing is the most convenient tool for providing a global perspective of aerosols and PWV, ground-based photometric techniques play an important role in climate studies They are especially valuable for validating satellite AOD and PWV products, as well as powerful tools for model assimilation and evaluation. Sun photometers appear as one of the most suitable ground-based techniques for estimating near-real PWV time with high spatial coverage [31,32] because of the relatively low cost and easy deployment of this type of instrument These characteristics have allowed the establishment of several global and international networks of sun photometers in the past decades: the World Meteorological Organization (WMO) Global Atmosphere Watch Precision Filter Radiometer (GAW-PFR) network [33], the China Aerosol Remote Sensing NETwork, (CARSNET) [34], SKYNET [35] and the Aerosol Robotic NETwork (AERONET) [36]. A summary of this study and the main conclusions are provided in the last Section
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