Abstract
Manually collected snow data are often considered as ground truth for many applications such as climatological or hydrological studies. However, there are many sources of uncertainty that are not quantified in detail. For the determination of water equivalent of snow cover (SWE), different snow core samplers and scales are used, but they are all based on the same measurement principle. We conducted two field campaigns with 9 samplers commonly used in observational measurements and research in Europe and northern America to better quantify uncertainties when measuring depth, density and SWE with core samplers. During the first campaign, as a first approach to distinguish snow variability measured at the plot and at the point scale, repeated measurements were taken along two 20 m long snow pits. The results revealed a much higher variability of SWE at the plot scale (resulting from both natural variability and instrumental bias) compared to repeated measurements at the same spot (resulting mostly from error induced by observers or very small scale variability of snow depth). The exceptionally homogeneous snowpack found in the second campaign permitted to almost neglect the natural variability of the snowpack properties and focus on the separation between instrumental bias and error induced by observers. Under such measurement conditions, the uncertainty in bulk snow density estimation is about 5% for an individual instrument and is close to 10% among different instruments. Results confirmed that instrumental bias exceeded both the natural variability and the error induced by observers, even in the case when observers were not familiar with a given snow core sampler.
Highlights
Water equivalent of snow cover (SWE) is one of the most commonly measured snowpack properties (Pirazzini et al, 2018)
5 CONCLUSIONS The results of the field campaigns provided a unique opportunity to analyze the uncertainty of measurements of bulk snow density and water equivalent of snow cover (SWE) carried out with snow core samplers that are regularly used in many European countries and beyond
The main conclusions can be enumerated as follows: - In snowpack subjected to natural variability at small scales, as it was the case in the Iceland campaign, the variability between close measurement points exceeded the one observed between repetitions at the same spot, the latter is still high
Summary
Water equivalent of snow cover (SWE) is one of the most commonly measured snowpack properties (Pirazzini et al, 2018). SWE is commonly used in long-term climatological or hydrological studies (Marty, 2017; Helmert et al, 2018), and as data for calibration, evaluation, or assimilation of remote sensing and numerical models (Dong, 2018). Long-term measurements are used for developing statistical models (e.g. Jonas et al, 2009) that can be used in combination with LiDAR measurements and other depth measurements over space (Schöber et al, 2014) or in the framework of snow data assimilation (Magnusson et al, 2014). SWE can either be measured automatically by pressure sensors (Johnson, 2004), or retrieved by various emerging techniques like Global Navigation Satellite System antennas (Guttmann et al, 2012; Koch et al, 2014), radiofrequency transmission lines (Stähli et al, 2004), passive gamma-ray sensors (Choquette et al, 2013), cosmic-ray neutron sensors (Schattan et al, 2017) or ground penetrating radar (Schmid et al, 2015). Microwave remote instruments, both active and passive, proved their capability to estimate information on SWE (Takala et al, 2011), there are clear limitations in mountain regions
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