Intercomparison of measurements of bulk snow density and water
equivalent of snow cover with snow core samplers: instrumental bias and
variability induced by observers
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.