Leaf biochemical properties have been widely assessed using hyperspectral reflectance information by inversion of PROSPECT model or by using hyperspectral indices, but few studies have focused on arid ecosystems. As a...Leaf biochemical properties have been widely assessed using hyperspectral reflectance information by inversion of PROSPECT model or by using hyperspectral indices, but few studies have focused on arid ecosystems. As a dominant species of riparian ecosystems in arid lands, Populus euphratica Oliv. is an unusual tree species with polymorphic leaves along the vertical profile of canopy corresponding to different growth stages. In this study, we evaluated both the inversed PROSPECT model and hyperspectral indices for estimating biochemical properties of P. euphratica leaves. Both the shapes and biochemical properties of P. euphratica leaves were found to change with the heights from ground surface. The results indicated that the model inversion calibrated for each leaf shape performed much better than the model calibrated for all leaf shapes, and also better than hyperspectral indices. Similar results were obtained for estimations of equivalent water thickness (EWT) and leaf mass per area (LMA). Hyperspectral indices identified in this study for estimating these leaf properties had root mean square error (RMSE) and R2 values between those obtained with the two calibration strategies using the inversed PROSPECT model. Hence, the inversed PROSPECT model can be applied to estimate leaf biochemical properties in arid ecosystems, but the calibration to the model requires special attention.展开更多
青藏高原及其周边区域通常被称为地球“第三极”.它不仅是受全球气候变暖影响最显著的区域之一,同时也是全球冰湖溃决洪水(Glacial Lake Outburst Floods,GLOFs)灾害频发的地区之一.尽管之前已经有很多发生在第三极地区的GLOF事件被报道...青藏高原及其周边区域通常被称为地球“第三极”.它不仅是受全球气候变暖影响最显著的区域之一,同时也是全球冰湖溃决洪水(Glacial Lake Outburst Floods,GLOFs)灾害频发的地区之一.尽管之前已经有很多发生在第三极地区的GLOF事件被报道,但考虑到GLOFs通常发生在高海拔无人区以及一些小规模的GLOFs并没有对下游地区造成太大的破坏,可能仍然有一些已经发生的GLOF事件并没有被发现和报道.基于此假设,本文借助大量高分辨率的卫星影像和3个GLOF发生后遗留的典型地貌形态特征对整个第三极地区6万多个冰湖进行了全面和系统地检查,最终识别出176个之前没有被记录的GLOF源头,其中167个来自冰碛坝湖,9个来自基岩坝湖.这一数量是所有已报道GLOF源头数量(75个)的2倍多.综合这些新发现的和已报道的GLOF案例,本文总结出第三极地区GLOF高发的4个热点地区为:喜马拉雅、冈底斯山、念青唐古拉山和天山地区.这些新识别的GLOF案例将为未来的研究提供重要的基础,从而有助于更好地认识和理解第三极地区GLOF的发生机理及真实的发生频率.展开更多
基金supported by the West Light Talents Cultivation Program of Chinese Academy of Sciences (XBBS 200801)the National Natural Science Foundation of China (40801146)the JSPS Project (21403001)
文摘Leaf biochemical properties have been widely assessed using hyperspectral reflectance information by inversion of PROSPECT model or by using hyperspectral indices, but few studies have focused on arid ecosystems. As a dominant species of riparian ecosystems in arid lands, Populus euphratica Oliv. is an unusual tree species with polymorphic leaves along the vertical profile of canopy corresponding to different growth stages. In this study, we evaluated both the inversed PROSPECT model and hyperspectral indices for estimating biochemical properties of P. euphratica leaves. Both the shapes and biochemical properties of P. euphratica leaves were found to change with the heights from ground surface. The results indicated that the model inversion calibrated for each leaf shape performed much better than the model calibrated for all leaf shapes, and also better than hyperspectral indices. Similar results were obtained for estimations of equivalent water thickness (EWT) and leaf mass per area (LMA). Hyperspectral indices identified in this study for estimating these leaf properties had root mean square error (RMSE) and R2 values between those obtained with the two calibration strategies using the inversed PROSPECT model. Hence, the inversed PROSPECT model can be applied to estimate leaf biochemical properties in arid ecosystems, but the calibration to the model requires special attention.
基金This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences(XDA19030301,XDA20030101)A special acknowledgment is to China-Pakistan Joint Research Center on Earth Sciences that supported the implementation of this study.Guoxiong Zheng thanks the China Scholarship Council for supporting his visit to the University of Geneva from February 2019 to February 2021(201804910569).
文摘青藏高原及其周边区域通常被称为地球“第三极”.它不仅是受全球气候变暖影响最显著的区域之一,同时也是全球冰湖溃决洪水(Glacial Lake Outburst Floods,GLOFs)灾害频发的地区之一.尽管之前已经有很多发生在第三极地区的GLOF事件被报道,但考虑到GLOFs通常发生在高海拔无人区以及一些小规模的GLOFs并没有对下游地区造成太大的破坏,可能仍然有一些已经发生的GLOF事件并没有被发现和报道.基于此假设,本文借助大量高分辨率的卫星影像和3个GLOF发生后遗留的典型地貌形态特征对整个第三极地区6万多个冰湖进行了全面和系统地检查,最终识别出176个之前没有被记录的GLOF源头,其中167个来自冰碛坝湖,9个来自基岩坝湖.这一数量是所有已报道GLOF源头数量(75个)的2倍多.综合这些新发现的和已报道的GLOF案例,本文总结出第三极地区GLOF高发的4个热点地区为:喜马拉雅、冈底斯山、念青唐古拉山和天山地区.这些新识别的GLOF案例将为未来的研究提供重要的基础,从而有助于更好地认识和理解第三极地区GLOF的发生机理及真实的发生频率.