Refractive index model to determine the vulnerability curves for different building typologies

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

10.5194/amt-2021-103 ◽

2021 ◽

Author(s):

Hiroshi Ishimoto ◽

Masahiro Hayashi ◽

Yuzo Mano

Keyword(s):

Refractive Index ◽

Brightness Temperature ◽

Volcanic Ash ◽

Satellite Measurements ◽

Temperature Spectrum ◽

Index Model ◽

Rock Types ◽

Volcanic Events ◽

Atmospheric Sounding ◽

Using Data

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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