Fibre-optic distributed temperature monitoring (DTS) system at a boreal forest PFRR site: Loop 1

A fibre-optic DTS (distributed temperature sensing) system using Raman-scattering optical time domain reflectometry was deployed to monitor a boreal forest research site in the interior of Alaska. Surface temperatures range between -40º C in winter to 30º C in summer at this site. The ground surface and subsurface thermal states were monitored at high-resolution (0.5-metre intervals every 30 minutes) with a fibre-optic cable sensor system (multi-mode, GI50/125?dual core; 3.4 mm). The total cable ran 2.7 km with about 2.0 km monitoring a horizontal surface path. Sections of the cable sensor were deployed in vertical coil configurations (1.2 m high) to measure vertical temperature profiles from the ground up at 5-mm intervals. Measurements were collected continuously over a two year interval from October, 2012 to October, 2014. Vegetation of the overall site (Poker Flat Research Range) consists primarily of black spruce underlain by permafrost. Land cover types within the study area were classified into six descriptive categories: relict thermokarst lake, open moss, shrub, deciduous forest, sparse conifer forest, and dense conifer forest. The horizontal temperature data exhibited spatio-temporal patterns within the observed diurnal and seasonal variation. Differences in snow pack evolution and insulation effects co-varied with the land cover types. The apparatus used to monitor vertical temperature profiles generated high-resolution (c. 5 mm) data for air column, snow cover, and ground surface.