Abstract
Abstract. Continuous and spatially distributed data of snow mass (water equivalent of snow cover, SWE) from automatic ground-based measurements are increasingly required for climate change studies and for hydrological applications (snow hydrological-model improvement and data assimilation). We present and compare four new-generation sensors, now commercialized, that are non-invasive and based on different radiations that interact with snow for SWE monitoring: cosmic-ray neutron probe (CRNP), gamma ray monitoring (GMON) scintillator, frequency-modulated continuous-wave radar (FMCW radar) at 24 GHz and global navigation satellite system (GNSS) receivers (GNSSr). All four techniques have relatively low power requirements, provide continuous and autonomous SWE measurements, and can be easily installed in remote areas. A performance assessment of their advantages, drawbacks and uncertainties is discussed from experimental comparisons and a literature review. Relative uncertainties are estimated to range between 9 % and 15 % when compared to manual in situ snow surveys that are also discussed. Results show the following. (1) CRNP can be operated in two modes of functioning: beneath the snow, it is the only system able to measure very deep snowpacks (> 2000 mm w.e.) with reasonable uncertainty across a wide range of measurements; CRNP placed above the snow allows for SWE measurements over a large footprint (∼ 20 ha) above a shallow snowpack. In both cases, CRNP needs ancillary atmospheric measurements for SWE retrieval. (2) GMON is the most mature instrument for snowpacks that are typically up to 800 mm w.e. Both CRNP (above snow) and GMON are sensitive to surface soil moisture. (3) FMCW radar needs auxiliary snow-depth measurements for SWE retrieval and is not recommended for automatic SWE monitoring (limited to dry snow). FMCW radar is very sensitive to wet snow, making it a very useful sensor for melt detection (e.g., wet avalanche forecasts). (4) GNSSr allows three key snowpack parameters to be estimated simultaneously: SWE (range: 0–1000 mm w.e.), snow depth and liquid water content, according to the retrieval algorithm that is used. Its low cost, compactness and low mass suggest a strong potential for GNSSr application in remote areas.
Highlights
Snow cover on the ground surface plays an important role in the climate system due to its high albedo, heat insulation that affects the ground thermal regime, and contribution to snow runoff and soil moisture (Meredith et al, 2019)
The instruments were located in an open area (Fig. 2e) of the Montmorency experimental forest (47.32◦ N, 71.15◦ W; 640 m a.s.l.) of Université Laval (Québec City), which is in the boreal forest
Results show that gamma ray monitoring (GMON) and cosmic-ray neutron probe (CRNP) evolve over the winter, with GMON snow cover (SWE) being slightly higher after the first winter month (SWE > 50 mm)
Summary
Snow cover on the ground surface plays an important role in the climate system due to its high albedo, heat insulation that affects the ground thermal regime, and contribution to snow runoff and soil moisture (Meredith et al, 2019). Surface-based radar scatterometers and microwave radiometers have not been considered in this study because (1) they are still in early stages of development or are currently not operational and (2) they have heavy maintenance demands (not autonomous) and are still relatively expensive These include, for example, scatterometers (Werner et al, 2010; Wiesmann et al, 2010; King et al, 2015; Werner et al, 2019), microwave radiometers (Langlois, 2015; Roy et al, 2016, 2017; Wiesmann et al, 2021), radar interferometers (Werner et al, 2010; Leinss et al, 2015; Pieraccini and Miccinesi, 2019; GPRI brochure, 2021) and stepped-frequency continuous-wave radar (SFCW) instruments (Alonso et al, 2021). 3.1 and 3.2: comparisons between EDF’s (Électricité de France) CRNP (NRC sensor; nivomètre à rayonnement cosmique) and GMON on one hand and GNSSr, FMCW radar and GMON on the other hand This permits performance evaluations for each system, including uncertainty analysis, compared to manual SWE measurements. Listing of references cited in this article sorted by the sensor name: CNRP, FMCW-Radar, GNSSr, GMON, Radar, Radiometer and Snow core can be found in the Supplement
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