Northwest Territories and Nunavut Snow Characteristics from a Subarctic Traverse: Implications for Passive Microwave Remote Sensing

Abstract

During April 2007, a coordinated series of snow measurements was made across the Northwest Territories and Nunavut, Canada, during a snowmobile traverse from Fairbanks, Alaska, to Baker Lake, Nunavut. The purpose of the measurements was to document the general nature of the snowpack across this region for the evaluation of satellite- and model-derived estimates of snow water equivalent (SWE). Although detailed, local snow measurements have been made as part of ongoing studies at tundra field sites (e.g., Daring Lake and Trail Valley Creek in the Northwest Territories; Toolik Lake and the Kuparak River basin in Alaska), systematic measurements at the regional scale have not been previously collected across this region of northern Canada. The snow cover consisted of depth hoar and wind slab with small and ephemeral fractions of new, recent, and icy snow. The snow was shallow (<40 cm deep), usually with fewer than six layers. Where snow was deposited on lake and river ice, it was shallower, denser, and more metamorphosed than where it was deposited on tundra. Although highly variable locally, no longitudinal gradients in snow distribution, magnitude, or structure were detected. This regional homogeneity allowed us to identify that the observed spatial variability in passive microwave brightness temperatures was related to subgrid fractional lake cover. Correlation analysis between lake fraction and Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) brightness temperature showed frequency dependent, seasonally evolving relationships consistent with lake ice drivers. Simulations of lake ice thickness and snow depth on lake ice produced from the Canadian Lake Ice Model (CLIMo) indicated that at low frequencies (6.9, 10.7 GHz), correlations with lake fraction were consistent through the winter season, whereas at higher frequencies (18.7, 36.5 GHz), the strength and direction of the correlations evolved consistently with the penetration depth as the influence of the subice water was replaced by emissions from the ice and snowpack. A regional rain-on-snow event created a surface ice lens that was detectable using the AMSR-E 36.5-GHz polarization gradient due to a strong response at the horizontal polarization. The appropriate polarization for remote sensing of the tundra snowpack depends on the application: horizontal measurements are suitable for ice lens detection; vertically polarized measurements are appropriate for deriving SWE estimates.

Frequency and distribution of winter melt events from passive microwave satellite data in the pan-Arctic, 1988–2013

“…Due to large temporal gaps in the early SSM/I record, the time series used begin in the fall of 1988 and extend to 2014 (Table 1). Although horizontal polarized measurements are more sensitive to ice lenses within the snowpack (Derksen et al, 2009;Rees et al, 2010), there is not much difference between the two polarizations for melt detection and we use vertically polarized measurements to be consistent with Wang et al (2013).…”

Variability and change in the Canadian cryosphere

“…Canada's IPY activities also spurred unique observational campaigns conducted across the Canadian Arctic. During April 2007, a coordinated series of snow measurements was made across the Northwest Territories and Nunavut, during a 4200 km snowmobile traverse from Fairbanks, Alaska, to Baker Lake, Nunavut (Derksen et al 2009). In another unique campaign, Canadian IPY scientists partnered with the Canadian Rangers, a group of highlyskilled reservists from Nunavut, Yukon and the Northwest Territories who train and patrol with the Canadian Forces.…”

“…The boreal forest cover across the sub-Arctic taiga and the highly heterogeneous distribution of Arctic snow cover tend to increase passive microwave SWE retrieval uncertainties when simple brightness temperature difference algorithms are applied. Further uncertainties are introduced by the vertically heterogeneous Arctic snowpack with dense, fine-grained wind slabs overlying loose large grained depth hoar, and by a high fraction of lakes which complicate microwave emission in some regions (Derksen et al 2009). To develop new algorithms that address these challenges, three airborne campaigns were conducted across the Canadian sub-Arctic between February and April 2008 (see Derksen et al 2010 andLanglois et al 2011).…”

Sodankylä manual snow survey program

“…Therefore, vertical changes of macrostructural parameters, such as temperature and density, are related to the evolution of snow microstructure. However, the structure of snowpack is very complex and spatial variations are large even on a small scale (Rutter et al, 2014;Derksen et al, 2009). Therefore, manual observations of snow macro-and microstructure have an important role in the monitoring of temporal evolution and spatial variations of snowpack.…”