Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling.
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| Title: | Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling. |
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| Authors: | Saxby, Jennifer1 (AUTHOR) jennifer.saxby@bristol.ac.uk, Rust, Alison1 (AUTHOR), Beckett, Frances2 (AUTHOR), Cashman, Katharine1 (AUTHOR), Rodger, Hannah1 (AUTHOR) |
| Source: | Earth & Planetary Science Letters. Mar2020, Vol. 534, pN.PAG-N.PAG. 1p. |
| Subjects: | Volcanic ash, tuff, etc., Volcanic eruptions, Atmospheric models, Computed tomography, Sedimentation & deposition, Shape measurement |
| Abstract: | • X-ray CT is an efficient method of measuring bulk 3D shape parameters. • Shape parameters based on principal axis lengths are more robust than surface area. • Volcanic ash particle shape is a function of particle size. • Shape-dependent drag equations are more accurate than a spherical approximation. The sedimentation rate of volcanic ash through the atmosphere influences its travel distance, with important implications for aviation and health. The fall velocity of a particle depends on its size and density, but also shape, and volcanic ash is not spherical. To capture the sedimentation of ash, atmospheric dispersion models use empirical drag equations calibrated using geometric shape descriptors. However, particle shape data are scarce and there is no standard method of shape measurement. In addition, shape measurements are not always available during an eruption, when dispersion models are used operationally to forecast ash hazard. We assess the variability in the shape of volcanic ash from Icelandic eruptions using X-ray computed tomography. To consider how good different drag equations and shape descriptors are at representing the sedimentation of volcanic ash we compare calculated fall velocities to measured fall velocities of volcanic ash in air in a settling column. We then suggest the best drag equations and shape descriptors for use in atmospheric dispersion models. We find that shape-dependent drag equations produce more accurate results than a spherical approximation. However, accurate drag calculations based on the shape descriptor sphericity, which is a function of surface area, require the imaging resolution to be within the range of 102 - 105 voxels per particle (where a voxel is a volumetric pixel) as surface area is sensitive to imaging resolution. We suggest that the large-scale form of the particle impacts sedimentation more than small-scale surface roughness. Shape descriptors based on ratios between principal axis lengths are more practical as they are less variable among particle size classes and much less sensitive to imaging resolution. Finally, we use particle shape data from this study and literature sources to make recommendations on default values for use with atmospheric dispersion models where no shape data are available. [ABSTRACT FROM AUTHOR] |
| Copyright of Earth & Planetary Science Letters is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
| FullText | Text: Availability: 0 |
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| Header | DbId: egs DbLabel: Engineering Source An: 141939384 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Saxby%2C+Jennifer%22">Saxby, Jennifer</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> jennifer.saxby@bristol.ac.uk</i><br /><searchLink fieldCode="AR" term="%22Rust%2C+Alison%22">Rust, Alison</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Beckett%2C+Frances%22">Beckett, Frances</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Cashman%2C+Katharine%22">Cashman, Katharine</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Rodger%2C+Hannah%22">Rodger, Hannah</searchLink><relatesTo>1</relatesTo> (AUTHOR) – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Earth+%26+Planetary+Science+Letters%22">Earth & Planetary Science Letters</searchLink>. Mar2020, Vol. 534, pN.PAG-N.PAG. 1p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Volcanic+ash%2C+tuff%2C+etc%2E%22">Volcanic ash, tuff, etc.</searchLink><br /><searchLink fieldCode="DE" term="%22Volcanic+eruptions%22">Volcanic eruptions</searchLink><br /><searchLink fieldCode="DE" term="%22Atmospheric+models%22">Atmospheric models</searchLink><br /><searchLink fieldCode="DE" term="%22Computed+tomography%22">Computed tomography</searchLink><br /><searchLink fieldCode="DE" term="%22Sedimentation+%26+deposition%22">Sedimentation & deposition</searchLink><br /><searchLink fieldCode="DE" term="%22Shape+measurement%22">Shape measurement</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: • X-ray CT is an efficient method of measuring bulk 3D shape parameters. • Shape parameters based on principal axis lengths are more robust than surface area. • Volcanic ash particle shape is a function of particle size. • Shape-dependent drag equations are more accurate than a spherical approximation. The sedimentation rate of volcanic ash through the atmosphere influences its travel distance, with important implications for aviation and health. The fall velocity of a particle depends on its size and density, but also shape, and volcanic ash is not spherical. To capture the sedimentation of ash, atmospheric dispersion models use empirical drag equations calibrated using geometric shape descriptors. However, particle shape data are scarce and there is no standard method of shape measurement. In addition, shape measurements are not always available during an eruption, when dispersion models are used operationally to forecast ash hazard. We assess the variability in the shape of volcanic ash from Icelandic eruptions using X-ray computed tomography. To consider how good different drag equations and shape descriptors are at representing the sedimentation of volcanic ash we compare calculated fall velocities to measured fall velocities of volcanic ash in air in a settling column. We then suggest the best drag equations and shape descriptors for use in atmospheric dispersion models. We find that shape-dependent drag equations produce more accurate results than a spherical approximation. However, accurate drag calculations based on the shape descriptor sphericity, which is a function of surface area, require the imaging resolution to be within the range of 102 - 105 voxels per particle (where a voxel is a volumetric pixel) as surface area is sensitive to imaging resolution. We suggest that the large-scale form of the particle impacts sedimentation more than small-scale surface roughness. Shape descriptors based on ratios between principal axis lengths are more practical as they are less variable among particle size classes and much less sensitive to imaging resolution. Finally, we use particle shape data from this study and literature sources to make recommendations on default values for use with atmospheric dispersion models where no shape data are available. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Earth & Planetary Science Letters is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1016/j.epsl.2020.116075 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 1 StartPage: N.PAG Subjects: – SubjectFull: Volcanic ash, tuff, etc. Type: general – SubjectFull: Volcanic eruptions Type: general – SubjectFull: Atmospheric models Type: general – SubjectFull: Computed tomography Type: general – SubjectFull: Sedimentation & deposition Type: general – SubjectFull: Shape measurement Type: general Titles: – TitleFull: Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Saxby, Jennifer – PersonEntity: Name: NameFull: Rust, Alison – PersonEntity: Name: NameFull: Beckett, Frances – PersonEntity: Name: NameFull: Cashman, Katharine – PersonEntity: Name: NameFull: Rodger, Hannah IsPartOfRelationships: – BibEntity: Dates: – D: 15 M: 03 Text: Mar2020 Type: published Y: 2020 Identifiers: – Type: issn-print Value: 0012821X Numbering: – Type: volume Value: 534 Titles: – TitleFull: Earth & Planetary Science Letters Type: main |
| ResultId | 1 |
