Retrieval of aerosol properties from zenith sky radiance measurements
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Published:2023-10-09
Issue:19
Volume:16
Page:4423-4443
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ISSN:1867-8548
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Container-title:Atmospheric Measurement Techniques
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language:en
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Short-container-title:Atmos. Meas. Tech.
Author:
Herrero-Anta SaraORCID, Román RobertoORCID, Mateos DavidORCID, González RamiroORCID, Antuña-Sánchez Juan Carlos, Herreras-Giralda Marcos, Almansa Antonio FernandoORCID, González-Fernández Daniel, Herrero del Barrio Celia, Toledano CarlosORCID, Cachorro Victoria E., de Frutos Ángel M.
Abstract
Abstract. This study explores the potential to retrieve aerosol properties
with the GRASP algorithm (Generalized Retrieval of Atmosphere and Surface
Properties) using as input measurements of zenith sky radiance (ZSR), which
are sky radiance values measured in the zenith direction, recorded at four
wavelengths by a ZEN-R52 radiometer. To this end, the ZSR measured at 440,
500, 675 and 870 nm by a ZEN-R52 (ZSRZEN), installed in Valladolid
(Spain), is employed. This instrument is calibrated by intercomparing the
signal of each channel with coincident ZSR values simulated (ZSRSIM) at
the same wavelengths with a radiative transfer model (RTM). These
simulations are carried out using the GRASP forward module as RTM and the
aerosol information from a co-located CE318 photometer belonging to
AERONET (AErosol RObotic NETwork) as input. The dark signal and the
signal dependence on temperature are characterized and included in the
calibration process. The uncertainties for each channel are quantified by an
intercomparison with a co-located CE318 photometer, obtaining lower values
for shorter wavelengths; they are between 3 % for 440 nm and 21 % for 870 nm. The
proposed inversion strategy for the aerosol retrieval using the ZSRZEN
measurements as input, i.e. so-called GRASP-ZEN, assumes the aerosol as an
external mixture of five pre-calculated aerosol types. A sensitivity
analysis is conducted using synthetic ZSRZEN measurements, pointing out
that these measurements are sensitive to aerosol load and type. It also
assesses that the retrieved aerosol optical depth (AOD) values in general
overestimate the reference ones by 0.03, 0.02, 0.02 and 0.01 for 440, 500,
675 and 870 nm, respectively. The calibrated ZSRZEN measurements, recorded
during 2.5 years at Valladolid, are inverted by the GRASP-ZEN strategy
to retrieve some aerosol properties like AOD. The retrieved AOD shows a high
correlation with respect to independent values obtained from a co-located
AERONET CE318 photometer, with determination coefficients (r2) of
0.86, 0.85, 0.79 and 0.72 for 440, 500, 675 and 870 nm, respectively, and
finding uncertainties between 0.02 and 0.03 with respect to the AERONET
values. Finally, the retrieval of other aerosol properties, like aerosol
volume concentration for total, fine and coarse modes (VCT, VCF and VCC, respectively), is
also explored. The comparison against independent values from AERONET
presents r2 values of 0.57, 0.56 and 0.66 and uncertainties of 0.009,
0.016 and 0.02 µm3 µm−2 for VCT, VCF and VCC, respectively.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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