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| Titel |
Recovering long-term aerosol optical depth series (1976–2012) from an astronomical potassium-based resonance scattering spectrometer |
| VerfasserIn |
A. Barreto, E. Cuevas, P. Pallé, P. M. Romero, C. Guirado, C. J. Wehrli, F. Almansa |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 7, no. 12 ; Nr. 7, no. 12 (2014-12-03), S.4103-4116 |
| Datensatznummer |
250115973
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| Publikation (Nr.) |
 copernicus.org/amt-7-4103-2014.pdf |
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| Zusammenfassung |
| A 37-year long-term
series of monochromatic aerosol optical depth (AOD) has been
recovered from solar irradiance measurements performed with the
solar spectrometer Mark-I, deployed at Izaña mountain since
1976. The instrument operation is based on the method of resonant
scattering, which affords wavelength absolute reference and stability
(long-term stability and high precision)
in comparison to other instruments based purely on interference
filters. However, it has been specifically designed as a reference
instrument for helioseismology, and its ability to determine AOD from
transmitted and scattered monochromatic radiation at 769.9 nm inside
a potassium vapour cell in the presence of a permanent magnetic field
is evaluated in this paper. Particularly, the use of an exposed
mirror arrangement to collect sunlight as well as the
Sun–laboratory velocity dependence of the scattered component
introduces some important inconveniences to overcome
when we perform the instrument's calibration. We have solved this problem
using a quasi-continuous
Langley calibration technique and a refinement procedure to correct
for calibration errors as well as for the fictitious diurnal cycle
on AOD data. Our results showed similar calibration errors retrieved
by means of this quasi-continuous Langley technique applied in different
aerosol load events (from 0.04 to 0.3),
provided aerosol concentration remains constant
throughout the calibration interval. It assures the validity of this
technique when it is applied in
those periods with relatively high aerosol content. The comparative analysis
between the recovered AOD data set from the Mark-I and collocated
quasi-simultaneous data from the Cimel-AErosol RObotic NETwork (AERONET)
and Precision Filter Radiometer (PFR) instruments showed an absolute
mean bias ≤ 0.01 in the 10- and 12-year comparison,
respectively. High correlation coefficients between AERONET and Mark-I
and PFR/Mark-I pairs confirmed a very good linear relationship
between instruments, proving that recovered AOD data series from
Mark-I can be used together with PFR and AERONET AOD data to build
a long-term AOD data series at the Izaña site (1976–now), suitable for
future analysis of aerosols trends and inter-annual
variability. Finally, the AOD preliminary trend analysis in the
29-year period from 1984 to 2012 with Mark-I AOD revealed no
significant trends. |
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