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Limitations of Using a Thermal Imager for Snow Pit Temperatures : Volume 8, Issue 2 (11/03/2014)

By Schirmer, M.

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Book Id: WPLBN0003984155
Format Type: PDF Article :
File Size: Pages 8
Reproduction Date: 2015

Title: Limitations of Using a Thermal Imager for Snow Pit Temperatures : Volume 8, Issue 2 (11/03/2014)  
Author: Schirmer, M.
Volume: Vol. 8, Issue 2
Language: English
Subject: Science, Cryosphere
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2014
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Jamieson, B., & Schirmer, M. (2014). Limitations of Using a Thermal Imager for Snow Pit Temperatures : Volume 8, Issue 2 (11/03/2014). Retrieved from http://worldlibrary.org/


Description
Description: Department of Civil Engineering, University of Calgary, Calgary, Canada. Driven by temperature gradients, kinetic snow metamorphism plays an import role in avalanche formation. When gradients based on temperatures measured 10 cm apart appear to be insufficient for kinetic metamorphism, faceting close to a crust can be observed. Recent studies that visualised small-scale (< 10 cm) thermal structures in a profile of snow layers with an infrared (IR) camera produced interesting results. The studies found melt-freeze crusts to be warmer or cooler than the surrounding snow depending on the large-scale gradient direction. However, an important assumption within these studies was that a thermal photo of a freshly exposed snow pit was similar enough to the internal temperature of the snow. In this study, we tested this assumption by recording thermal videos during the exposure of the snow pit wall. In the first minute, the results showed increasing gradients with time, both at melt-freeze crusts and artificial surface structures such as shovel scours. Cutting through a crust with a cutting blade or shovel produced small concavities (holes) even when the objective was to cut a planar surface. Our findings suggest there is a surface structure dependency of the thermal image, which was only observed at times during a strong cooling/warming of the exposed pit wall. We were able to reproduce the hot-crust/cold-crust phenomenon and relate it entirely to surface structure in a temperature-controlled cold laboratory. Concave areas cooled or warmed more slowly compared with convex areas (bumps) when applying temperature differences between snow and air. This can be explained by increased radiative and/or turbulent energy transfer at convex areas. Thermal videos suggest that such processes influence the snow temperature within seconds. Our findings show the limitations of using a thermal camera for measuring pit-wall temperatures, particularly during windy conditions, clear skies and large temperature differences between air and snow. At crusts or other heterogeneities, we were unable to create a sufficiently planar snow pit surface and non-internal gradients appeared at the exposed surface. The immediate adjustment of snow pit temperature as it reacts with the atmosphere complicates the capture of the internal thermal structure of a snowpack with thermal videos. Instead, the shown structural dependency of the IR signal may be used to detect structural changes of snow caused by kinetic metamorphism. The IR signal can also be used to measure near surface temperatures in a homogenous new snow layer.

Summary
Limitations of using a thermal imager for snow pit temperatures

Excerpt
Dozier, J. and Warren, S.: Effect of viewing angle on the infrared brightness temperature of snow, Water Resour. Res., 18, 1424–1434, 1982.; Hori, M., Aoki, T., Tanikawa, T., Motoyoshi, H., Hachikubo, A., Sugiura, K., Yasunari, T. J., Eide, H., Storvold, R., Nakajima, Y., and Takahashi, F.: In-situ measured spectral directional emissivity of snow and ice in the 8–14 μm atmospheric window, Remote Sens. Environ., 100, 486–502, 2006.; Hori, M., Aoki, T., Tanikawa T., Hachikubo, A., Sugiura, K., Kuchiki, K., and Niwano, M.: Modeling angular-dependent spectral emissivity of snow and ice in the thermal infrared atmospheric window, Applied Optics, 52, 30, 7243–7255, 2013.; Jamieson, B.: Formation of refrozen snowpack layers and their role in slab avalanche release, Rev. Geophys., 44, RG2001, doi:10.1029/2005RG000176, 2006.; Korb, A. R., Salisbury, J. W., and D'Aria, D. M.: Thermal-infrared remote sensing and Kirchhoff's law: 2. Field measurements, J. Geophys. Res.-Sol. Ea., 104, 15339–15350, 1999.; Pinzer, B. R., Schneebeli, M., and Kaempfer, T. U.: Vapor flux and recrystallization during dry snow metamorphism under a steady temperature gradient as observed by time-lapse micro-tomography, The Cryosphere, 6, 1141–1155, doi:10.5194/tc-6-1141-2012, 2012.; Riche, F. and Schneebeli, M.: Thermal conductivity of snow measured by three independent methods and anisotropy considerations, The Cryosphere, 7, 217–227, doi:10.5194/tc-7-217-2013, 2013.; Salisbury, J. W., D'Aria, D. M., and Wald, A.: Measurements of thermal infrared spectral reflectance of frost, snow, and ice, J. Geophys. Res.-Sol. Ea., 99, 24235–24240, 1994a.; Salisbury, J. W., Wald, A., and D'Aria, D. M.: Thermal-infrared remote sensing and Kirchhoff's law: 1. Laboratory measurements, J. Geophys. Res.-Sol. Ea., 99, 11897–11911, 1994b.; Shea, C. and Jamieson, B.: Some fundamentals of handheld snow surface thermography, The Cryosphere, 5, 55–66, doi:10.5194/tc-5-55-2011, 2011.; Shea, C., Jamieson, B., and Birkeland, K.: Hot crust, cold crust, Avalanche Review, 30, p. 28, 2012a.; Shea, C., Jamieson, B., and Birkeland, K.: Using a thermal imager to quantify buried thermal structure in natural snow, in: Proceedings of the International Snow Science Workshop 2012, Anchorage, AK, USA, 269–276, 2012b.; Shea, C., Jamieson, B., and Birkeland, K. W.: Use of a thermal imager for snow pit temperatures, The Cryosphere, 6, 287–299, doi:10.5194/tc-6-287-2012, 2012c.; Smith, M. and Jamieson, B.: Tracking changes in buried melt freeze crusts, in: Proceedings of the International Snow Science Workshop 2009, Davos, Switzerland, 107–111, 2009.

 

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