Spatio-temporally continuous temperature monitoring using optical fibers in the internal forest areas in Alaska

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 -40 C in winter and 30 C in summer at this site. In parallel experiments, a fibre-optic cable sensor system (multi-mode, GI50/125, dual core; 3.4 mm), monitored at high resolution, (0.5m intervals at every 30 min) ground surface temperatures across the landscape. In addition, a highresolution vertical profile was acquired at one-metre height above the upper subsurface. 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 (1.2m high) to measure temperature profiles from the ground up at 5mm intervals. Measurements were made continuously over a 2-year interval from October 2012 to October 2014. Vegetation at the 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 spatial and temporal changes within the observed diurnal and seasonal variations. 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 (ca. 5 mm) data for air column, snow cover, and ground surface.本研究采用基于拉曼散射光时域反射计（Raman-scattering optical time domain reflectometry）的光纤分布式温度传感（DTS, distributed temperature sensing）系统，对阿拉斯加内陆的一处北方森林研究场地开展监测。该场地地表冬季最低气温可达-40℃，夏季最高气温可达30℃。 在并行对照实验中，一套多模、GI50/125、双芯、外径3.4mm的光缆传感器系统以高分辨率模式（每30分钟采集一次0.5米间隔的温度数据），对研究区全域地表温度进行监测。此外，在地下表层上方1米高度处获取了高分辨率垂直温度剖面。整套光缆总长2.7km，其中约2.0km用于水平地表路径的温度监测。部分光缆传感器采用垂直盘管构型（高度1.2m），以5mm的间隔采集从地面向上的温度剖面数据。本次监测于2012年10月至2014年10月间连续开展，时长共计2年。 该研究场地（波弗特平原研究靶场，Poker Flat Research Range）的植被以黑云杉为主，地下分布多年冻土（permafrost）。研究区内的土地覆盖类型可分为6类：残余热喀斯特湖、开阔苔藓地、灌丛、落叶林、稀疏针叶林及稠密针叶林。水平温度监测数据展现出观测到的昼夜与季节尺度内的时空变化特征。积雪演化与保温效应的差异与土地覆盖类型呈协同变化关系。 用于监测垂直温度剖面的装置可获取空气柱、积雪层与地表的高分辨率（约5mm）监测数据。