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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 10, 565-579, 2017
http://www.atmos-meas-tech.net/10/565/2017/
doi:10.5194/amt-10-565-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
20 Feb 2017
A new zenith-looking narrow-band radiometer-based system (ZEN) for dust aerosol optical depth monitoring
A. Fernando Almansa1,2,4, Emilio Cuevas1, Benjamín Torres3, África Barreto1,2, Rosa D. García1,5, Victoria E. Cachorro4, Ángel M. de Frutos4, César López6, and Ramón Ramos1 1Izaña Atmospheric Research Center (IARC), Meteorological State Agency of Spain (AEMET), Santa Cruz de Tenerife, 38001, Spain
2Cimel Electronique, Paris, 75011, France
3Laboratoire d'Optique Amosphérique, UMR8518, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France
4Group of Atmospheric Optics, University of Valladolid, Valladolid, 47011, Spain
5Air Liquide España, Delegación Canarias, Candelaria, 38509, Spain
6Sieltec Canarias S.L., La Laguna, 38230, Spain
Abstract. A new zenith-looking narrow-band radiometer based system (ZEN), conceived for dust aerosol optical depth (AOD) monitoring, is presented in this paper. The ZEN system comprises a new radiometer (ZEN-R41) and a methodology for AOD retrieval (ZEN-LUT). ZEN-R41 has been designed to be stand alone and without moving parts, making it a low-cost and robust instrument with low maintenance, appropriate for deployment in remote and unpopulated desert areas. The ZEN-LUT method is based on the comparison of the measured zenith sky radiance (ZSR) with a look-up table (LUT) of computed ZSRs. The LUT is generated with the LibRadtran radiative transfer code. The sensitivity study proved that the ZEN-LUT method is appropriate for inferring AOD from ZSR measurements with an AOD standard uncertainty up to 0.06 for AOD500 nm  ∼  0.5 and up to 0.15 for AOD500 nm  ∼  1.0, considering instrumental errors of 5 %. The validation of the ZEN-LUT technique was performed using data from AErosol RObotic NETwork (AERONET) Cimel Electronique 318 photometers (CE318). A comparison between AOD obtained by applying the ZEN-LUT method on ZSRs (inferred from CE318 diffuse-sky measurements) and AOD provided by AERONET (derived from CE318 direct-sun measurements) was carried out at three sites characterized by a regular presence of desert mineral dust aerosols: Izaña and Santa Cruz in the Canary Islands and Tamanrasset in Algeria. The results show a coefficient of determination (R2) ranging from 0.99 to 0.97, and root mean square errors (RMSE) ranging from 0.010 at Izaña to 0.032 at Tamanrasset. The comparison of ZSR values from ZEN-R41 and the CE318 showed absolute relative mean bias (RMB)  <  10 %. ZEN-R41 AOD values inferred from ZEN-LUT methodology were compared with AOD provided by AERONET, showing a fairly good agreement in all wavelengths, with mean absolute AOD differences  <  0.030 and R2 higher than 0.97.

Citation: Almansa, A. F., Cuevas, E., Torres, B., Barreto, Á., García, R. D., Cachorro, V. E., de Frutos, Á. M., López, C., and Ramos, R.: A new zenith-looking narrow-band radiometer-based system (ZEN) for dust aerosol optical depth monitoring, Atmos. Meas. Tech., 10, 565-579, doi:10.5194/amt-10-565-2017, 2017.
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Short summary
This study presents a new zenith-looking narrow-band radiometer-based system (ZEN), conceived for dust aerosol optical depth (AOD) monitoring. The ZEN system comprises a robust and automated radiometer (ZEN-R41), and a lookup table methodology for AOD retrieval (ZEN-LUT). Our results suggest that ZEN is a suitable system to fill the current observational gaps and to complement observations performed by sun-photometer networks in order to improve mineral dust monitoring in remote locations.
This study presents a new zenith-looking narrow-band radiometer-based system (ZEN), conceived...
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