Arctic Wild Fire Research using Multi Satellite Sensors (UAF's campus site)

The research site was located at a typical taiga forest in central Alaska (64 o 51'58.57"N, 147 o 51'19.93"W), which stands on discontinuous permafrost. The vegetation of this site is composed of black spruce, short shrub, vascular plants, lichen and moss. The height of the black spruce around the observation tower was up to 6 m, but most were less than 1.5 m, and the density including short trees was 5000 trees/ha. The shrub height was less than 0.8 m, and the forest floor was tussock tundra with a height about 0.2-0.3 m. The permafrost soil thawed from spring to mid summer with the maximum depth of around 0.5 m. CO2 flux and energy balance (sensible heat and latent heat) were measured by an eddy correlation method using an open path CO2/H2O fluctuation meter (LiCor, LI7500) and a sonic anemometer (Campbell, CSAT-3). CH4 concentration was measured by a FID-GA (Flame Ionized Detector type-Gas Analyzer: Horiba, FIA-510). Ambient air at two heights of the tower (2 and 8 m) was sampled continuously with the CH4 analyzer, and the CH4 concentration at each height was measured. The CH4 flux was determined by the modified gradient method (Miyata et al., 2000), by using 30-min average data concentrations, sensible heat flux, friction velocity, and atmospheric stability.本研究的野外观测站点位于阿拉斯加中部一处典型泰加林（Taiga Forest），地理坐标为64°51'58.57"N、147°51'19.93"W，该区域发育不连续多年冻土。该站点的植被群落由黑云杉（Black Spruce）、矮灌木、维管植物、地衣与苔藓构成。观测塔周边的黑云杉株高最高可达6米，但多数植株高度不足1.5米，含幼树在内的种群密度达5000株/公顷。灌木株高低于0.8米，林地表层为草丘苔原，高度约0.2~0.3米。该多年冻土的活动层于春季至仲夏期间解冻，最大解冻深度约0.5米。本研究采用涡度相关法（eddy correlation method）测定CO₂通量与能量平衡（显热通量与潜热通量），所用设备包括开路式CO₂/H₂O脉动分析仪（LiCor LI7500）与超声风速仪（Campbell CSAT-3）。甲烷（CH₄）浓度则采用火焰离子化检测器型气体分析仪（Flame Ionized Detector type-Gas Analyzer，简称FID-GA，Horiba FIA-510）测定。研究人员通过甲烷分析仪连续采集观测塔2米与8米高度处的环境空气样品，并同步测定两个高度的甲烷浓度。甲烷通量则通过改进梯度法（modified gradient method，Miyata等，2000）计算，计算所用数据为30分钟平均的浓度值、显热通量、摩擦速度与大气稳定度参数。