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| Titel |
Use of rotational Raman measurements in multiwavelength aerosol lidar for evaluation of particle backscattering and extinction |
| VerfasserIn |
I. Veselovskii, D. N. Whiteman, M. Korenskiy, A. Suvorina, D. Pérez-Ramírez |
| 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 ; 8, no. 10 ; Nr. 8, no. 10 (2015-10-07), S.4111-4122 |
| Datensatznummer |
250116627
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| Publikation (Nr.) |
 copernicus.org/amt-8-4111-2015.pdf |
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| Zusammenfassung |
| Vibrational Raman scattering from nitrogen is commonly used in aerosol
lidars for evaluation of particle backscattering (β) and extinction
(α) coefficients. However, at mid-visible wavelengths, particularly
in the daytime, previous measurements have possessed low signal-to-noise
ratio. Also, vibrational scattering is characterized by a significant
frequency shift of the Raman component, so for the calculation of α
and β information about the extinction Ångström exponent is
needed. Simulation results presented in this study demonstrate that
ambiguity in the choice of Ångström exponent can be the a significant
source of uncertainty in the calculation of backscattering coefficients when
optically thick aerosol layers are considered. Both of these issues are
addressed by the use of pure-rotational Raman (RR) scattering, which is
characterized by a higher cross section compared to nitrogen vibrational
scattering, and by a much smaller frequency shift, which essentially removes
the sensitivity to changes in the Ångström exponent. We describe a
practical implementation of rotational Raman measurements in an existing
Mie–Raman lidar to obtain aerosol extinction and backscattering at 532 nm. A
2.3 nm width interference filter was used to select a spectral range
characterized by low temperature sensitivity within the anti-Stokes branch
of the RR spectrum. Simulations demonstrate that the temperature dependence
of the scattering cross section does not exceed 1.5 % in the 230–300 K
range, making correction for this dependence quite easy. With this upgrade,
the NASA GSFC multiwavelength Raman lidar has demonstrated useful α532 measurements and was used for regular observations. Examples of
lidar measurements and inversion of optical data to the particle
microphysics are given. |
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