Simulation and Validation of the InfraSnow: An Instrument to Measure Snow Optically Equivalent Grain Size

Abstract

Quantifying snow grain size is crucial to analyze radiative transfer and mechanical interactions in the snow cover. We present a nondestructive method for fast measurements of snow optically equivalent diameter (OED). The method consists of diffuse near-infrared reflectance measurements by a compact integrating sphere setup to derive OED. This principle is realized in the handheld InfraSnow instrument. The correlation between snow OED and reflectance is calculated by applying Monte Carlo ray tracing to a 3-D implementation of the measurement geometry. Including the geometrical boundary conditions is essential to obtain a good agreement between modeled and measured InfraSnow reflectance values. In addition to InfraSnow reflectance, snow density is required as second input parameter to the OED analysis. Our InfraSnow OED measurements agree with reference OED measurements by micro computed tomography (micro-CT) within 25% for seven of the ten tested snow blocks. Furthermore, the relative differences between both measurement methods are close to the estimated uncertainties of the InfraSnow methodology. If density is measured by micro-CT and then used as InfraSnow model input to derive OED, an average agreement with the reference micro-CT OED values within 13% is found. If density is measured by a permittivity sensor, the average agreement is within 20%.

European In-Situ Snow Measurements: Practices and Purposes

“…The snow specific surface area (SSA) is measured only by six respondents (from Finland, France, Italy, Switzerland, and the U.K.), each of them generally applying several techniques that were developed only recently. This is the case for the IceCube that was developed in France [ 11 ] and was utilized in Finland, France, Switzerland, and the U.K.; the SnowMicroPen was developed in Switzerland [ 13 ] and was applied in France, Switzerland, and the U.K.; the NIR-photography method was developed in Switzerland [ 28 ] and is applied in Italy (Insubria University), Switzerland (WSL Institute for Snow and Avalanche Research), and the U.K. (Northumbria University); the ASSSAP [ 12 ] was developed and is applied in France; and the InfraSnow [ 29 ] was developed and is applied in Switzerland. These new techniques are much more practical and ‘portable’ than the more traditional methods that are based on gas absorption or micro-computed tomography, which require specialized laboratories.…”

“… Snow surface temperature Snow presence (portable or stationary, non-invasive, passive, and automatic) Infrared sensor, Probe A handheld infrared sensor probe can be applied to quickly measure the vertical profile of snow temperature in a snowpit, immediately after the cut of the wall. Snow temperature (portable or stationary, non-invasive, passive, manual with electronics or automatic) InfraSnow The InfraSnow instrument measures optical equivalent grain size, which can be converted to specific surface area [ 29 ]. The instrument uses a light-emitting diode with a wavelength of 950 nm and a photodetector.…”

Measuring Snow Specific Surface Area with 1.30 and 1.55 μm Bidirectional Reflectance Factors

“…Compared to the Infrasnow(Gergely et al, 2014), NERD BRF measurements of Lambertian surfaces are slightly less accurate. In a similar validation experiment,Gergely et al (2014) measure the reflectance of 0.25, 0.50, and 0.99 reflectance stan-10 dards accurately to within less than 1 % Gergely et al (2014). use an integrating sphere that enables directional-hemispherical reflectance factor measurements at 950 nm in contrast to the 1.30 and 1.55 µm BRFs measured by the NERD.…”

“…for initial snow SSA 0 at t = 0 and adjustable parameters τ and n. Previous studies establish techniques to accurately obtain snow SSA using methane gas absorption (Legagneux et al, 2002), contact spectroscopy (Painter et al, 2007), infrared hemispherical reflectance (Gallet et al, 2009;Picard et al, 2009;Gallet et al, 2014;Gergely et al, 2014), and X-CT in cold rooms (Pinzer and Schneebeli, 2009;Wang and Baker, 2014;Ebner et al, 2015), but these methods require expensive, heavy equipment and measurements can be time consuming. Further, previous methods require that snow samples are collected and possibly even destroyed during measurements, preventing in situ snow 5 observations over the span of just several hours.…”

Evaluation of the Snow Thermal Model (SNTHERM) through Continuous in situ Observations of Snow’s Physical Properties at the CREST-SAFE Field Experiment

“…Differences between the observed and simulated snow grain size are associated with the manual method (microscope) used to estimate in situ snow grain size, which represents the average size of several grains collected in a random sample. The accuracy of this measurement has been questioned [56] and it is hypothesized to be the cause of the discrepancies between observations and simulations. Even though, Figures 13 and 14 depicts that observed and simulated grain size are within range.…”