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Investigation of single scattering properties of snow based on first order Legendre phase function
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0002-5943-1476
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
Norwegian University of Science and Technology.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-4879-8261
Number of Authors: 4
2017 (English)In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 91, p. 151-159Article in journal (Refereed) Published
Abstract [en]

Angularly resolved bidirectional reflectance measurements were modelled by ap- proximating a first order Legendre expanded phase function to retrieve single scattering properties of snow. The measurements from 10 different snow types with known density and specific surface area (SSA) were investigated. A near infrared (NIR) spectrometer was used to measure reflected light above the snow surface over the hemisphere in the wavelength region 900 nm to 1650 nm. A solver based on discrete ordinate radiative transfer (DISORT) model was used to retrieve the estimated Legendre coefficients of the phase function and a cor- relation between the coefficients and physical properties of different snow types is investigated. Results of this study suggest that the first two coefficients of the first order Legendre phase function provide sufficient information about the physical properties of snow where the latter captures the anisotropic behaviour of snow and the former provides a relative estimate of the single scattering albedo of snow. The coefficients of the first order phase function were com- pared with the experimental data and observed that both the coefficients are in good agreement with the experimental data. These findings suggest that our approach can be applied as a qualitative tool to investigate physical properties of snow and also to classify different snow types.

Place, publisher, year, edition, pages
2017. Vol. 91, p. 151-159
Keyword [en]
Radiative transfer model, Scattering phase function, Snow, SSA, Reflectance spectrum, NIR spectrometer
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-60532DOI: 10.1016/j.optlaseng.2016.11.013ISI: 000393264300016Scopus ID: 2-s2.0-84998694302OAI: oai:DiVA.org:ltu-60532DiVA, id: diva2:1047645
Note

Validerad; 2017; Nivå 2; 2016-12-19 (andbra)

Available from: 2016-11-18 Created: 2016-11-18 Last updated: 2018-04-18Bibliographically approved
In thesis
1. Experimental investigation of snow metamorphism at near-surface layers
Open this publication in new window or tab >>Experimental investigation of snow metamorphism at near-surface layers
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Snow metamorphism is a direct objective in many snow research areas, and its charactization is a major challenge in areas including winter road maintenance, detection of icing on wind turbine blades and snow quality mapping for skiing. The snow metamorphism in response to level and type of compaction associated with variations in physical properties of snow. While the compaction influence on snow metamorphism in relation to snow physical properties is fairly known, the relation between the compaction and physical properties of snow is not extensively understood. This experimental based thesis study presents three different approaches to investigate the snow metamorphism in response to compaction. Considered snow types during the thesis, experienced compaction via aging, melting-freezing process, applying uniaxial load, settling and introducing liquid water. In addition, the influence of snow compaction at near-surface layers is investigated using optical techniques.

In the first approach, near-infrared (NIR) light scattering from snow surfaces is numerically modelled based on the radiative transfer theory. The model used in this approach, was a special case of widely used Discrete Ordinates Radiative Transfer (DISORT) method that solves the radiative transfer equation for a plane-parallel and semi-infinite snowpack. This numerical methodology leads to a Legendre scattering phase function, where the link between the Legendre coefficients and physical properties of snow in relation to compaction is investigated. The observations in this approach show the consistency and strong correlation between the Legendre coefficients and physical properties of snow. The second approach of the thesis, was focused on statistical analysis of NIR reflectance measurements from snow surfaces for the determination of snow properties. In this approach, physical properties of snow such as specific surface area (SSA) and surface liquid water content (LWC) are quantified via parameterization where the reflectance data is used as input. In both of these approaches, compaction of a snowpack is investigated and understood based on grain size distribution, surface texture, snow temperature and scattering behaviour of NIR radiation. As a next step, the snow compaction is investigated on a microscopic level where a X-ray microtomography (micro-CT) was used to model the three dimensional (3D) microstructure of snow. In this approach, evolution and deformation of snow grains during compaction via applying uniaxial load is investigated. In addition, snow compaction is understood based on digital volume correlation (DVC) and porosity analysis.

In summary, the thesis presents an experimental method to quantify the link between the snow compaction at near-surface layers and physical properties of snow. The model observations show that the estimated Legendre coefficients can provide qualitative description of snow grain distribution and surface texture. The parameterization observations show that the SSA of snow and snow surface LWC can be quantified from snow reflectance measurements. The observations from the micro-CT study show the influence of compaction at a granular level. The observations presented in the thesis, are helpful to understand the metamorphism in a snowpack for relevant research areas.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keyword
Snow metamorphism; NIR reflectance; Snow and Ice; Radiative transfer equation; Paramterization; Snow properties; Tomography; Snow microstructure
National Category
Other Materials Engineering Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-68394 (URN)978-91-7790-116-7 (ISBN)978-91-7790-117-4 (ISBN)
Public defence
2018-06-18, E231, Luleå University of Technology, Luleå, 15:48 (English)
Opponent
Supervisors
Available from: 2018-04-18 Created: 2018-04-18 Last updated: 2018-05-24Bibliographically approved

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Eppanapelli, Lavan KumarCasselgren, JohanSjödahl, Mikael

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