2000-2013年青藏高原湖泊面积MODIS遥感监测分析

Detection and Analysis of Qinghai-Tibet Plateau Lake Area from 2000 to 2013

青藏高原上分布着大量的高原内陆湖泊群,该区域湖泊面积与区域及全球气候变化之间存在较强的耦合关系,遥感监测湖泊的分布和面积变化趋势,对分析区域自然生态环境具有重要意义。本研究将MOD09A1(地表反射率8天合成数据)进行逐月合成,提出了一种综合多种水体指数的青藏高原地区湖泊提取方法,并通过活动窗口、DEM和时间序列去噪等方法,消除山体阴影、冰雪等因素的干扰。最后,提取和合成了2000-2013年青藏高原逐年和逐月的湖泊范围,并选取色林错和卓乃湖2个典型湖泊与人工解译Landsat系列影像进行验证分析,其线性拟合度分别为0.99和0.97,从时空变化趋势上分析了青藏高原湖泊面积动态变化。结果表明:(1)2000-2013年,青藏高原地区湖泊范围整体上呈较显著的扩张趋势,湖泊总面积增加速率约为490.98 km2a-1(R2约为0.96);(2)1-12月份湖泊面积逐月变化率均大于0,表明青藏高原湖泊面积呈整体扩张,而非季节性扩张。除2-4月份外,其他月份增加速率均在400 km2a-1以上(R2>0.79),表现为稳定且持续扩张趋势。

Qinghai-Tibet plateau is the world＇s highest and largest plateau which is surrounded by massive moun-tain ranges. There are plenty of lakes and glaciers covering this area, and the variation of lake area is closely re-lated to the regional and global climate changes. This paper presents a method using MODIS observations to quantify lake area in each month in Qinghai-Tibet plateau for 14 years, and then analyzes the change of lake area at both monthly and annually scales. MODIS surface reflectance data （MOD09A1） acquired within the period of each month are retrieved and composited to produce the optimal and cloud-free SR data of the month, which are adopted as the input data. In order to achieve better accuracy on water detection, multiple water indices are com-bined, and then the DEM and summer season water maps are adopted to remove noisy pixels caused by cloud, shadow, snow and ice. With this approach, the monthly and annually lake area is derived for Qinghai-Tibet pla-teau from 2000 to 2013.Subsequently,the accuracy of these results are evaluated by correlation coefficient calcu-lated with respect to the artificial interpreted Landsat products assigned as reference for Selin Co lake and Zhuon-ai lake, respectively. The comparisons show high consistency on both spatial and temporal aspects（R2 is 0.99 and 0.97）. Finally, the variation tendency of lakes in Qinghai-Tibet plateau is analyzed, the results show：（1） a stable increase is obvious （R2 is 0.96） for the lake area during the past 14 years with an average annual increase rate of 490.98 km2a-1;（2）monthly increment indicates lake expansion is unlikely due to seasonality in Qinghai-Tibet pla-teau. Stable increases （R2〉0.78, increase rate〉400 km2a-1） are also found in every month of the year except Feb-ruary, March and April.