MODIS,CYCLOPES和GLASS 3种LAI产品在韩江流域的对比

摘要

叶面积指数(leaf area index,LAI)是影响植被蒸腾、降水截留和能量交换的关键参数,是生态模型和陆面过程模型的重要输入参数.目前,全球许多机构基于多种遥感数据,采用不同的反演方法得到了多种LAI产品,MO-DIS,CYCLOPES和GLASS是其中时空分辨率较高的3种.以植被类型多样的韩江流域为对象,通过分析这3种LAI产品的空间和时间一致性,得到以下结论:①CYCLOPES LAI存在大量的数据缺失,MODIS和GLASS LAI具有更好的空间和时间序列的完整性;但MODIS LAI存在大量LAI突然变小的无效数据.②MODIS,CYCLOPES和GLASS LAI的空间分布基本都能与流域的植被类型相适应,其中,MODIS与GLASS LAI的空间分布一致性相对较好,但前者林地的LAI较后者大,非林地则相反;而CYCLOPES LAI林地的LAI明显比前两者的小.③MODIS,CY-CLOPES和GLASS LAI的时间序列过程线具有相同的变化趋势,GLASS LAI的过程曲线是3者中最完整和平滑的, MODIS LAI的曲线有明显的波动性.3种LAI反映的各种植被的季节变化具有较好的一致性,MODIS和GLASS LAI的相似程度比CYCLOPES LAI高.%Leaf area index (LAI) is a primary parameter for characterizing vegetation canopy structure. Since LAI can affect many vegetation ecological processes,such as transpiration,interception and energy exchange,it is used as a critical input for ecological models and land surface process models. At present, several global LAI datasets have been generated from different satellite remote sensing data,such as AVHRR,MODIS and VEGETATION,by different retrieval methods. MODIS, CYCLOPES and GLASS LAI datasets are those with higher spatial and temporal resolution. The spatial and temporal consistency of MODIS, CYCLOPES and GLASS LAI datasets was analyzed over Hanjiang River basin,which is covered with several vegetation types. Comparative study revealed the following characteristics: ① CYCLOPES LAI was observed to contain a large number of missing pixels, while MODIS and GLASS LAI products were more spatially and temporally complete. MODIS LAI contained many invalid pixels,whose LAI became much smaller abruptly in comparison with the LAI values just before or after this time.② The spatial distributions of MODIS, CYCLOPES and GLASS LAI were mainly consistent with the vegetation types of the basin. The spatial distributions of MODIS and GLASS LAI were more consistent than those of CYCLOPES LAI. MODIS LAI was larger than GLASS LAI in forest pixels, while it was contrary in other pixels. CYCLOPES LAI was much smaller than MODIS and GLASS LAI in forest pixels. ③ MODIS, CYCLOPES and GLASS LAI products generally depicted similar temporal trajectories. GLASS LAI had the smoothest and completest trajectories,while the trajectories of MODIS LAI contained a large number of erratic fluctuations. All of these three LAI products depicted similar seasonal changes for different vegetation types. Compared with CYCLOPES LAI, a good agreement was achieved between MODIS and GLASS LAI values.