Supplementary material to "Optimal ash particle refractive index model for simulating the brightness temperature spectrum of volcanic ash clouds from satellite infrared sounder measurements"

Abstract. Using data from the Infrared Atmospheric Sounding Interferometer (IASI) measurements of volcanic ash clouds and radiative transfer calculations, we identify the optimal refractive index model for simulating the measured brightness temperature spectrum of volcanic ash material. We assume that the optimal refractive index model has the smallest root mean square of the brightness temperature difference between measurements and simulations for channels in the wavenumber range of 750–1400 cm−1 and compare 21 refractive index models for optical properties of ash particles, including recently published models. From the results of numerical simulations for 164 pixels of IASI measurements for ash clouds from 11 volcanoes, we found that the measured brightness temperature spectrum could be well simulated using certain newly established refractive index models. In the cases of Eyjafjallajökull and Grímsvötn ash clouds, the optimal refractive index models determined through numerical simulation correspond to those deduced from the chemical composition of ash samples for the same volcanic eruption events. This finding suggests that infrared sounder measurement of volcanic ash clouds is an effective approach to estimating the optimal refractive index model. However, discrepancies between the estimated refractive index models based on satellite measurements and the associated volcanic rock types were observed for some volcanic events.

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Optimising the Complex Refractive Index Model for Estimating the Permittivity of Heterogeneous Concrete Models

Remote Sensing ◽

10.3390/rs13040723 ◽

2021 ◽

Vol 13 (4) ◽

pp. 723

Author(s):

Hossain Zadhoush ◽

Antonios Giannopoulos ◽

Iraklis Giannakis

Keyword(s):

Refractive Index ◽

Shape Factor ◽

Complex Refractive Index ◽

Fdtd Method ◽

Air Voids ◽

Water Fraction ◽

Index Model ◽

General Complex ◽

Ground Penetrating ◽

Fine Tune

Estimating the permittivity of heterogeneous mixtures based on the permittivity of their components is of high importance with many applications in ground penetrating radar (GPR) and in electrodynamics-based sensing in general. Complex Refractive Index Model (CRIM) is the most mainstream approach for estimating the bulk permittivity of heterogeneous materials and has been widely applied for GPR applications. The popularity of CRIM is primarily based on its simplicity while its accuracy has never been rigorously tested. In the current study, an optimised shape factor is derived that is fine-tuned for modelling the dielectric properties of concrete. The bulk permittivity of concrete is expressed with respect to its components i.e., aggregate particles, cement particles, air-voids and volumetric water fraction. Different combinations of the above materials are accurately modelled using the Finite-Difference Time-Domain (FDTD) method. The numerically estimated bulk permittivity is then used to fine-tune the shape factor of the CRIM model. Then, using laboratory measurements it is shown that the revised CRIM model over-performs the default shape factor and provides with more accurate estimations of the bulk permittivity of concrete.

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Optical, microphysical and compositional properties of the Eyjafjallajökull volcanic ash

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-13271-2014 ◽

2014 ◽

Vol 14 (9) ◽

pp. 13271-13300 ◽

Cited By ~ 3

Author(s):

A. Rocha-Lima ◽

J. V. Martins ◽

L. A. Remer ◽

N. A. Krotkov ◽

M. H. Tabacniks ◽

...

Keyword(s):

Refractive Index ◽

Volcanic Ash ◽

Fine Particles ◽

Absorption Efficiency ◽

Particle Sizes ◽

Air Volume ◽

Automatic Software ◽

Compositional Properties ◽

Size Distribution Of Particles ◽

Mass Absorption Efficiency

Abstract. Microphysical, optical, and compositional properties of the volcanic ash from the April–May (2010) Eyjafjallajökull volcanic eruption are presented. Samples of the volcanic ash were taken on the ground in the vicinity of the volcano. The material was sieved, re-suspended, and collected on filters, separating particle sizes into coarse and fine modes. The spectral mass absorption efficiency αabs [m2 g−1] was determined for coarse and fine particles in the wavelength range from 300 to 2500 nm. Size distribution of particles on filters was obtained using a semi-automatic software to analyze images obtained by Scanning Electron Microscopy (SEM). The grain density of the volcanic ash was determined as 2.16(13) g cm−3 by measuring the variation of air volume in a system with volcanic ash and air under compression. Using Mie–Lorenz and T-matrix theories, the imaginary part of the refractive index was derived. Results show the spectral imaginary refractive index ranging from 0.001 to 0.005. Fine and coarse particles were analyzed by X-Ray fluorescence for elemental composition. Fine and coarse mode particles exhibit distinct compositional and optical differences.

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