Employing relaxed smoothness constraints on imaginary part of refractive index in AERONET aerosol retrieval algorithm
In the Aerosol Robotic Network (AERONET) retrieval algorithm, smoothness constraints on the imaginary part of the refractive index provide control of retrieved spectral dependence of aerosol absorption by preventing the inversion code from fitting the noise in optical measurements and thus avoiding...
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ftcopernicus:oai:publications.copernicus.org:amt101515 2023-05-15T13:07:01+02:00 Employing relaxed smoothness constraints on imaginary part of refractive index in AERONET aerosol retrieval algorithm Sinyuk, Alexander Holben, Brent N. Eck, Thomas F. Giles, David M. Slutsker, Ilya Dubovik, Oleg Schafer, Joel S. Smirnov, Alexander Sorokin, Mikhail 2022-07-20 application/pdf https://doi.org/10.5194/amt-15-4135-2022 https://amt.copernicus.org/articles/15/4135/2022/ eng eng doi:10.5194/amt-15-4135-2022 https://amt.copernicus.org/articles/15/4135/2022/ eISSN: 1867-8548 Text 2022 ftcopernicus https://doi.org/10.5194/amt-15-4135-2022 2022-07-25T16:22:41Z In the Aerosol Robotic Network (AERONET) retrieval algorithm, smoothness constraints on the imaginary part of the refractive index provide control of retrieved spectral dependence of aerosol absorption by preventing the inversion code from fitting the noise in optical measurements and thus avoiding unrealistic oscillations of retrievals with wavelength. The history of implementation of the smoothness constraints in the AERONET retrieval algorithm is discussed. It is shown that the latest version of the smoothness constraints on the imaginary part of refractive index, termed standard and employed by Version 3 of the retrieval algorithm, should be modified to account for strong variability of light absorption by brown-carbon-containing aerosols in UV through mid-visible parts of the solar spectrum. In Version 3 strong spectral constraints were imposed at high values of the Ångström exponent (440–870 nm) since black carbon was assumed to be the primary absorber, while the constraints became increasingly relaxed as aerosol exponent deceased to allow for wavelength dependence of absorption for dust aerosols. The new version of the smoothness constraints on the imaginary part of the refractive index assigns different weights to different pairs of wavelengths, which are the same for all values of the Ångström exponent. For example, in the case of four-wavelength input, the weights assigned to short-wavelength pairs (440–675, 675–870 nm) are small so that smoothness constraints do not suppress natural spectral variability of the imaginary part of the refractive index. At longer wavelengths (870–1020 nm), however, the weight is 10 times higher to provide additional constraints on the imaginary part of refractive index retrievals of aerosols with a high Ångström exponent due to low sensitivity to aerosol absorption for longer channels at relatively low aerosol optical depths. The effect of applying the new version of smoothness constraints, termed relaxed, on retrievals of single-scattering albedo is analyzed for case ... Text Aerosol Robotic Network Copernicus Publications: E-Journals Atmospheric Measurement Techniques 15 14 4135 4151 |
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Copernicus Publications: E-Journals |
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ftcopernicus |
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English |
description |
In the Aerosol Robotic Network (AERONET) retrieval algorithm, smoothness constraints on the imaginary part of the refractive index provide control of retrieved spectral dependence of aerosol absorption by preventing the inversion code from fitting the noise in optical measurements and thus avoiding unrealistic oscillations of retrievals with wavelength. The history of implementation of the smoothness constraints in the AERONET retrieval algorithm is discussed. It is shown that the latest version of the smoothness constraints on the imaginary part of refractive index, termed standard and employed by Version 3 of the retrieval algorithm, should be modified to account for strong variability of light absorption by brown-carbon-containing aerosols in UV through mid-visible parts of the solar spectrum. In Version 3 strong spectral constraints were imposed at high values of the Ångström exponent (440–870 nm) since black carbon was assumed to be the primary absorber, while the constraints became increasingly relaxed as aerosol exponent deceased to allow for wavelength dependence of absorption for dust aerosols. The new version of the smoothness constraints on the imaginary part of the refractive index assigns different weights to different pairs of wavelengths, which are the same for all values of the Ångström exponent. For example, in the case of four-wavelength input, the weights assigned to short-wavelength pairs (440–675, 675–870 nm) are small so that smoothness constraints do not suppress natural spectral variability of the imaginary part of the refractive index. At longer wavelengths (870–1020 nm), however, the weight is 10 times higher to provide additional constraints on the imaginary part of refractive index retrievals of aerosols with a high Ångström exponent due to low sensitivity to aerosol absorption for longer channels at relatively low aerosol optical depths. The effect of applying the new version of smoothness constraints, termed relaxed, on retrievals of single-scattering albedo is analyzed for case ... |
format |
Text |
author |
Sinyuk, Alexander Holben, Brent N. Eck, Thomas F. Giles, David M. Slutsker, Ilya Dubovik, Oleg Schafer, Joel S. Smirnov, Alexander Sorokin, Mikhail |
spellingShingle |
Sinyuk, Alexander Holben, Brent N. Eck, Thomas F. Giles, David M. Slutsker, Ilya Dubovik, Oleg Schafer, Joel S. Smirnov, Alexander Sorokin, Mikhail Employing relaxed smoothness constraints on imaginary part of refractive index in AERONET aerosol retrieval algorithm |
author_facet |
Sinyuk, Alexander Holben, Brent N. Eck, Thomas F. Giles, David M. Slutsker, Ilya Dubovik, Oleg Schafer, Joel S. Smirnov, Alexander Sorokin, Mikhail |
author_sort |
Sinyuk, Alexander |
title |
Employing relaxed smoothness constraints on imaginary part of refractive index in AERONET aerosol retrieval algorithm |
title_short |
Employing relaxed smoothness constraints on imaginary part of refractive index in AERONET aerosol retrieval algorithm |
title_full |
Employing relaxed smoothness constraints on imaginary part of refractive index in AERONET aerosol retrieval algorithm |
title_fullStr |
Employing relaxed smoothness constraints on imaginary part of refractive index in AERONET aerosol retrieval algorithm |
title_full_unstemmed |
Employing relaxed smoothness constraints on imaginary part of refractive index in AERONET aerosol retrieval algorithm |
title_sort |
employing relaxed smoothness constraints on imaginary part of refractive index in aeronet aerosol retrieval algorithm |
publishDate |
2022 |
url |
https://doi.org/10.5194/amt-15-4135-2022 https://amt.copernicus.org/articles/15/4135/2022/ |
genre |
Aerosol Robotic Network |
genre_facet |
Aerosol Robotic Network |
op_source |
eISSN: 1867-8548 |
op_relation |
doi:10.5194/amt-15-4135-2022 https://amt.copernicus.org/articles/15/4135/2022/ |
op_doi |
https://doi.org/10.5194/amt-15-4135-2022 |
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Atmospheric Measurement Techniques |
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15 |
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14 |
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4135 |
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4151 |
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1766031395741761536 |