Civil Engineering
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The Department of Civil Engineering has strong affiliation with the Western Transportation Institute (WTI) and the Center for Biofilm Engineering (CBE), a graduated NSF research center. The department is also affiliated with a Montana Department of Transportation Design Unit located on the MSU campus.
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Item Mapping liquid water content in snow at the millimeter scale: an intercomparison of mixed-phase optical property models using hyperspectral imaging and in situ measurements(Copernicus Publications, 2022-01) Donahue, Christopher; Skiles, S. McKenzie; Hammonds, KevinIt is well understood that the distribution and quantity of liquid water in snow is relevant for snow hydrology and avalanche forecasting, yet detecting and quantifying liquid water in snow remains a challenge from the micro- to the macro-scale. Using near-infrared (NIR) spectral reflectance measurements, previous case studies have demonstrated the capability to retrieve surface liquid water content (LWC) of wet snow by leveraging shifts in the complex refractive index between ice and water. However, different models to represent mixed-phase optical properties have been proposed, including (1) internally mixed ice and water spheres, (2) internally mixed water-coated ice spheres, and (3) externally mixed interstitial ice and water spheres. Here, from within a controlled laboratory environment, we determined the optimal mixed-phase optical property model for simulating wet snow reflectance using a combination of NIR hyperspectral imaging, radiative transfer simulations (Discrete Ordinate Radiative Transfer model, DISORT), and an independent dielectric LWC measurement (SLF Snow Sensor). Maps of LWC were produced by finding the lowest residual between measured reflectance and simulated reflectance in spectral libraries, generated for each model with varying LWC and grain size, and assessed against the in situ LWC sensor. Our results show that the externally mixed model performed the best, retrieving LWC with an uncertainty of ∼1 %, while the simultaneously retrieved grain size better represented wet snow relative to the established scaled band area method. Furthermore, the LWC retrieval method was demonstrated in the field by imaging a snowpit sidewall during melt conditions and mapping LWC distribution in unprecedented detail, allowing for visualization of pooling water and flow features.Item In Situ Effective Snow Grain Size Mapping Using a Compact Hyperspectral Imager(2021-02) Donahue, Christopher; Skiles, S. McKenzie; Hammonds, KevinEffective snow grain radius (re) is mapped at high resolution using near-infrared hyperspectral imaging (NIR-HSI). The NIR-HSI method can be used to quantify re spatial variability, change in re due to metamorphism, and visualize water percolation in the snowpack. Results are presented for three different laboratory-prepared snow samples (homogeneous, ice lens, fine grains over coarse grains), the sidewalls of which were imaged before and after melt induced by a solar lamp. The spectral reflectance in each ~3 mm pixel was inverted for re using the scaled band area of the ice absorption feature centered at 1030 nm, producing re maps consisting of 54 740 pixels. All snow samples exhibited grain coarsening post-melt as the result of wet snow metamorphism, which is quantified by the change in re distributions from pre- and post-melt images. The NIR-HSI method was compared to re retrievals from a field spectrometer and X-ray computed microtomography (micro-CT), resulting in the spectrometer having the same mean re and micro-CT having 23.9% higher mean re than the hyperspectral imager. As compact hyperspectral imagers become more widely available, this method may be a valuable tool for assessing re spatial variability and snow metamorphism in field and laboratory settings.Item Quantifying damage in polycrystalline ice via X-Ray computed micro-tomography(2017-04) Hammonds, Kevin; Baker, Ian T.The use of X-ray computed micro-tomography (micro-CT) is presented here as a useful tool for the analysis and quantification of damage in polycrystalline ice. Although known to be useful for characterizing damage in many other materials, the use of micro-CT has not yet been adapted to the non-trivial case of also characterizing damage in polycrystalline ice. Samples of polycrystalline ice were tested in uniaxial compression at six different strain rates, spanning four orders of magnitude, from 1 × 10−6 s−1 to 1 × 10−3 s−1, and two different testing temperatures of −10 °C and −20 °C. The extent of cracking from each test is characterized via micro-CT imaging and is quantified via a newly proposed variant of the crack density tensor, which accounts for any anisotropy in the mean crack orientation and is shown to be equivalent to the materials anisotropy tensor. To account for anisotropy in the distribution of cracks, an eigenanalysis is also performed. The results show that micro-CT can be a useful tool for both visualizing and quantifying damage in polycrystalline ice and that a 3-D analog of the traditional second-rank crack density tensor can be readily calculated via commercially available software.