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Estimation of a low-order Legendre expanded phase function of snow
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.ORCID-id: 0000-0002-5943-1476
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.ORCID-id: 0000-0003-4879-8261
2016 (engelsk)Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 78, s. 174-181Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The purpose of this paper is to estimate the scattering phase function of snow from angularly resolved measurements of light intensity in the plane of incidence. A solver is implemented that solves the scattering function for a semi-infinite geometry based on the radiative transfer equation (RTE). Two types of phase functions are considered. The first type is the general phase function based on a low-order series expansion of Legendre polynomials and the other type is the Henyey-Greenstein (HG) phase function. The measurements were performed at a wavelength of 1310 nm and six different snow samples were analysed. It was found that a first order expansion provides sufficient approximation to the measurements. The fit from the first order phase function outperforms that of the HG phase function in terms of accuracy, ease of implementation and computation time. Furthermore, a correlation between the magnitude of the first order component and the age of the snow was found. We believe that these findings may complement present non-contact detection techniques used to determine snow properties.

sted, utgiver, år, opplag, sider
2016. Vol. 78, s. 174-181
HSV kategori
Forskningsprogram
Experimentell mekanik
Identifikatorer
URN: urn:nbn:se:ltu:diva-4108DOI: 10.1016/j.optlaseng.2015.10.013ISI: 000366769100021Scopus ID: 2-s2.0-84947210191Lokal ID: 1fb86369-88ce-4293-89e3-fae4460cfe1fOAI: oai:DiVA.org:ltu-4108DiVA, id: diva2:976972
Merknad
Validerad; 2015; Nivå 2; 20151028 (lavepp)Tilgjengelig fra: 2016-09-29 Laget: 2016-09-29 Sist oppdatert: 2018-07-10bibliografisk kontrollert
Inngår i avhandling
1. Experimental investigation of snow metamorphism at near-surface layers
Åpne denne publikasjonen i ny fane eller vindu >>Experimental investigation of snow metamorphism at near-surface layers
2018 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Alternativ tittel[sv]
Experimentell undersökning avsnömetamorfismen vid nära ytskikt
Abstract [en]

Snow metamorphism is a direct objective in many snow research areas, and its charac-terisation is a major challenge in areas including winter road maintenance, detection of icing on wind turbine blades, and snow quality mapping for skiing. A common effect of snow metamorphism is compaction, which can be investigated from the associated vari-ations in physical properties of snow. While the relation between snow metamorphism and physical properties of snow is fairly well-known, a method to quantify this relationis not extensively researched. This experimental based thesis focuses on the relationship between the physical properties of snow and its degree of metamorphism. The link isestablished and investigated by quantifying near-infrared (NIR) reflectance measure-ments and analysing the microtomographic data. Three experimental approaches are developed to record the NIR reflectance measurements and to understand the influence of compaction at near-surface layers of a snowpack. In addition, an X-ray microtomogra-phy (micro-CT) system is used to visualise the behaviour of snow microstructure during compaction. In this thesis, snow experienced compaction via aging, the melting-freezing process, uniaxial loading, settling and infiltration of liquid water.

A numerical tool based on the well-established Discrete Ordinates Radiative Trans-fer (DISORT) method is used to solve the radiative transfer equation (RTE) for aplane-parallel and semi-infinite snowpack. The numerical solver takes the reflectance measurements as input and returns the coefficients of a first order Legendre phase function of an investigated snowpack at a given wavelength of light. The results from the solver show consistency and strong correlation between the Legendre coefficient sand the physical properties of snow. Furthermore, the physical properties of snow such as specific surface area (SSA) and liquid water content (LWC) were estimated via parameterisation where the reflectance data is used as input. The results suggest that the parameterisation of LWC can provide a qualitative estimate of the LWC in a snowpack, while the parameterisation of SSA provides a quantitative estimate of the snow SSA. As a next step, the influence of compaction on snow microstructure is investigated from three-dimensional (3D) images obtained using the micro-CT system. In this case, compaction is initiated by applying uniaxial load on a snow sample and the effect of compaction is analysed based on digital volume correlation (DVC) and porosity distribution. The micro-CT observations further emphasise that near-surface layers of a snowpack experience a higher degree of impact during compaction.

In summary, this thesis presents experimental methods to quantify the link between snow compaction at near-surface layers, and the physical properties of snow. The mode observations show that the estimated Legendre coefficients can provide qualitative descriptions of snow grain distribution and surface texture. The parameterisation methods can provide the details about the LWC and the SSA of a snowpack. Further, the observations from the micro-CT study suggest that grains breakage and recrystallisation are the prevailing effects of snow compaction. All observations in this thesis are helpful in understanding the metamorphism in a snowpack for relevant research areas.

sted, utgiver, år, opplag, sider
Luleå: Luleå University of Technology, 2018
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Emneord
Snow metamorphism, NIR reflectance, Snow and Ice, Radiative transfer equation, Paramterization, Snow properties, Tomography, Snow microstructure
HSV kategori
Forskningsprogram
Experimentell mekanik
Identifikatorer
urn:nbn:se:ltu:diva-68394 (URN)978-91-7790-116-7 (ISBN)978-91-7790-117-4 (ISBN)
Disputas
2018-06-18, E 231, Luleå University of Technology, Luleå, 14:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2018-04-18 Laget: 2018-04-18 Sist oppdatert: 2019-09-11bibliografisk kontrollert

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