Abstract
High frequency (ultrasonic) acoustic wave propagation measurements were inverted to determine important near-surface parameters of snow including porosity, tortuosity, and pore geometry, using a newly-designed, oblique-reflection transducer apparatus. Acoustic signals interact with the physical structure of porous media, are particularly sensitive to porosity and tortuosity, and can be used to measure physical properties in a non-destructive manner. Given the fragile nature of freshly fallen snow, non-contact, non-destructive characterization methods made possible via acoustic signals, are desirable. High frequency wave propagation methods can be used to determine in situ near surface micro-pore geometry parameters in snow using methods demonstrated on cohesive porous materials including manufactured foams, porous metals, and sintered glass beads. Here, we conducted high frequency, oblique-angle and near vertical reflection measurements on snow samples to demonstrate the feasibility of acoustic response detection. We compared the acoustically derived snow physical parameters, including porosity and tortuosity, with values determined from X-ray micro-computed tomography (μCT) and gravimetric methods. Preliminary results using different snow types, and following the methods from previous work for cohesive porous media (i.e. fused glass beads) show good agreement between values of porosity determined from the acoustic measurements and the values determined from μCT image analysis.
Highlights
In the 1950s, Maurice Biot published a comprehensive mathematical theory of wave propagation in porous materials (Biot, 1956)
Three-dimensional (3D) binary reconstructions of representative examples for each of the four general classes of snow are shown in Figure 5 in order of age of snow
Aging of fresh snow over 1 day resulted in reduced surface to volume (S/V) ratios by roughly 17%
Summary
In the 1950s, Maurice Biot published a comprehensive mathematical theory of wave propagation in porous materials (Biot, 1956). The first experimental measurements to confirm the existence of the two compressional waves were published in 1980 (Plona, 1980; Smeulders, 2005), and since many modifications have been made to the theory. Properties of specific porous materials can be determined from reflected or transmitted acoustic waves using a classical inverse scattering mathematical approach (Horoshenkov, 2017). The interaction of sound energy with the ground is an important effect in understanding sound propagation in a natural setting, and is governed in part by the porous properties of the surface materials (Attenborough et al, 2011).
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