加拿大北方森林火烧迹地遥感分析

Burned Area Detection in the Canadian Boreal Forest Using MODIS Imagery

森林火灾是加拿大北方森林地区最主要的扰动因素,对北方生态系统起着主导作用。基于MODIS数据,采用全球扰动指数算法(MGDI),对加拿大萨斯喀彻温省和亚伯达省2004-2011年的森林火烧迹地进行检测和分析。通过与MODIS标准火烧迹地产品以及加拿大林业局数据进行比较,扰动指数算法检测的火烧迹地面积比MODIS标准产品更接近于林业局的统计数据。分析表明,在2004-2011年间,由于火灾原因,整个研究区森林面积平均每年减少76.36万hm2,占该区域森林总面积的3.36%。萨斯喀彻温省平均每年燃烧的森林面积为46.83万hm2,亚伯达省为29.53万hm2。其中,2006、2008、2010和2011年是火灾的高峰年份。火烧迹地主要集中在生态交错带的北方保护区、针叶林保护区、针叶林平原区,以及北方平原东北部的伍德布法罗国家森林保护区。

The boreal forest biome is one of the largest on earth,covering 17% of total land area.The major ecosystems within the boreal zone contain more than 30% of terrestrial carbon stores,thus representing a major component of the global carbon budget.Wildfires are a main disturbance factor in the Canadian boreal forests,which play an important role in boreal ecosystems.In this paper,we mapped the forest burned area in Saskatchewan and Alberta of Canada during 2004-2011,using two data sets of Moderate Resolution Imaging Spectroradiometer（MODIS） Land Surface Temperature（LST） and Enhanced Vegetation Index（EVI） imagery at 1 km resolution.The MODIS global disturbance index algorithm（MGDI） was used to detect the forest burned area.It is based on the consistent radiometric relationship between annual maximum LST and the maximum EVI value that occurs after the LST during the same year at every pixel.The performance of the algorithm was evaluated by comparing the results with the MODIS MCD45A1 products and the inventory data from Forestry Bureau of Canada.The results show that the majority of fire events is captured by the MGDI techniques,and the burned area estimated by the fires pixels is better in good agreement with the inventory data than MODIS products.Compared with the Canadian Forestry Bureau data,the average relative error of our algorithm results is only 8.03%,while the MODIS product results is up to 70.53%.The results estimated that the average burned forest area is about 763 600 ha annually,which is about 3.36% of the total forest in this region.A mean annual burned forest is 468 300 ha for Saskatchewan and 295 300ha for Alberta respectively.The Canadian boreal forest fires show a significant interannual variation and severity,the burned scar mainly appeared in the years of 2006,2008 and 2010-2011.Forest burned area mainly concentrated in the ecotone of the Boreal Shield,Taiga Shield,Taiga plains and the Wood Buffalo National Park located at the northeast of Boreal Plains.