Retrieval of aerosol refractive index from extinction spectra with a damped harmonic-oscillator band model

Thomas, G. E.; Bass, Stephen F.; Grainger, R. G.; Lambert, A.

doi:10.1364/ao.44.001332

Cited by 27 publications

(23 citation statements)

References 11 publications

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“…For example, when both refractive indices and particle size parameters are to be extracted from large aerosol particle spectra, the CDHO fitting can be employed where only a handful of parameters are need optimisation. 37,48 Based on the quantitative analysis in this study, we conclude that the Fourier series fitting is the most desirable method, especially when spectral features are not very narrow (> 10 cm -1 ). In cases where the spectral features are narrow (< 10 cm -1 ) the CDHO and the Triangular fitting are the most accurate and fast of the four methods.…”

Section: Discussionmentioning

confidence: 67%

“…Also note that the fitting is fastest (a few seconds) for the CDHO method due to its analytic nature and availability of analytic derivatives. 37 The triangular fitting converges similarly fast. The Fourier series fitting is also fast (tens of seconds), and it may be possible to accelerate further by evaluating series coefficients by Fast Fourier Transform.…”

Section: Fitting Of Acetonitrilementioning

confidence: 88%

“…47 Another advantage of CDHO fitting is the derivatives of the parameters to be optimised are readily available. 37 Thus CDHO fitting is one convenient method when further analysis is needed following the optical constants fitting. For example, when both refractive indices and particle size parameters are to be extracted from large aerosol particle spectra, the CDHO fitting can be employed where only a handful of parameters are need optimisation.…”

Section: Discussionmentioning

confidence: 99%

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Spectral curve fitting of dielectric constants

2017

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Optical constants are important properties governing the response of a material to incident light. It follows that they are often extracted from spectra measured by absorbance, transmittance or reflectance. One convenient method to obtain optical constants is by curve fitting. Here, model curves should satisfy Kramer-Kronig relations, and preferably can be expressed in closed form or easily calculable. In this study we use dielectric constants of three different molecular ices in the infrared region to evaluate four different model curves that are generally used for fitting optical constants: (1) the classical damped harmonic oscillator, (2) Voigt line shape, (3) Fourier series, and (4) the Triangular basis. Among these, only the classical damped harmonic oscillator model strictly satisfies the Kramer-Kronig relation. If considering the trade-off between accuracy and speed, Fourier series fitting is the best option when spectral bands are broad while for narrow peaks the classical damped harmonic oscillator and the Triangular basis fitting model are the best choice.

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Section: Discussionmentioning

confidence: 67%

Section: Fitting Of Acetonitrilementioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

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Spectral curve fitting of dielectric constants

2017

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“…Aerosols' IR optical properties during the ACE-Asia campaign were measured (Markowicz et al, 2003), and it was shown that the mean aerosol optical depth at 10 µm was 0.08 (for the entire atmospheric column). Apart from the complete optical depth, aerosol optical properties in the LWIR have been studied (Thomas et al, 2005;Richwine et al, 1995;Toon et al, 1976;Volz, 1972Volz, , 1973, and in addition, the effect of changes in the relative humidity on the extinction coefficients of atmospheric aerosols was presented (Nilsson, 1979). These properties can be incorporated in radiative transfer models in order to determine aerosols' radiative effect.…”

Section: Aerosolsmentioning

confidence: 99%

Determination of optical and microphysical properties of thin warm clouds using ground based hyper-spectral analysis

2012

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Abstract. Clouds play a critical role in the Earth's radiative budget as they modulate the atmosphere by reflecting shortwave solar radiation and absorbing long wave IR radiation emitted by the Earth's surface. Although extensively studied for decades, cloud modelling in global circulation models is far from adequate, mostly due to insufficient spatial resolution of the circulation models. In addition, measurements of cloud properties still need improvement, since the vast majority of remote sensing techniques are focused in relatively large, thick clouds. In this study, we utilize ground based hyperspectral measurements and analysis to explore very thin water clouds. These clouds are characterized by liquid water path (LWP) that spans from as high as ∼50g m −2 and down to 65 mg m −2 with a minimum of about 0.01 visible optical depth. The retrieval methodology relies on three elements: a detailed radiative transfer calculations in the longwave IR regime, signal enhancement by subtraction of a clear sky reference, and spectral matching method which exploits fine spectral differences between water droplets of different radii. A detailed description of the theoretical basis for the retrieval technique is provided along with a comprehensive discussion regarding its limitations. The proposed methodology was validated in a controlled experiment where artificial clouds were sprayed and their effective radii were both measured and retrieved simultaneously. This methodology can be used in several ways: (1) the frequency and optical properties of very thin water clouds can be studied more precisely in order to evaluate their total radiative forcing on the Earth's radiation budget. (2) The unique optical properties of the inter-region between clouds (clouds' "twilight zone") can be studied in order to more rigorously understanding of the governing physical processes which dominate this region.(3) Since the optical thickness of a developed cloud gradually decreases towards its edges, the proposed methodology can be used to study the spatial microphysical behaviour of these edges. (4) A spatial-temporal analysis can be used to study mixing processes in clouds' entrainment zone.

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“…et al, 1996). Laboratory based refractive indices estimation methods with spectral extinction measurements are proposed (Eiden R., 1971, Thomas G.E., et al, 2005. Refractive index and size distribution as well as single scattering albedo, Angstrome exponent, volume spectrum are, in general, estimated with ground based solar direct, diffuse and aureole data together with measured optical depth.…”

Section: Introductionmentioning

confidence: 99%

Method for Estimation of Aerosol Parameters Based on Ground Based Atmospheric Polarization Irradiance Measurements

Arai¹

2013

IJACSA

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Abstract-Method for aerosol refractive index estimation with ground based polarization measurement data is proposed. The proposed method uses a dependency of refractive index on p and s polarized down welling solar diffuse irradiance. It is much easy to measure p and s polarized irradiance on the ground with a portable measuring instrument rather than solar direct, diffuse and aureole measurements. Through theoretical and simulation studies, it is found that the proposed method show a good estimation accuracy of refractive index using measured down welling p and s polarized irradiance data with a measuring instrument pointing to the direction which is perpendicular to the sun in the principal plane. Field experimental results also show a validity of the proposed method in comparison to the estimated results from the conventional method with solar direct, diffuse and aureole measurement data.

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Retrieval of aerosol refractive index from extinction spectra with a damped harmonic-oscillator band model

Cited by 27 publications

References 11 publications

Spectral curve fitting of dielectric constants

Spectral curve fitting of dielectric constants

Determination of optical and microphysical properties of thin warm clouds using ground based hyper-spectral analysis

Method for Estimation of Aerosol Parameters Based on Ground Based Atmospheric Polarization Irradiance Measurements

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