Influence of heterogeneous landscapes on computed green-up dates based on daily AVHRR NDVI observations
Influence of heterogeneous landscapes on computed green-up dates based on daily AVHRR NDVI observations
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DOI：
10.1016/j.rse.2009.07.020
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发表时间：
2009-12-15
影响因子：
13.5
通讯作者：
Badeck, Franz-W
中科院分区：
文献类型：
--
作者：
Doktor, Daniel;Bondeau, Alberte;Badeck, Franz-W
本文件的主要目的是评估和解释根据卫星观测计算的植被地表绿化日期与根据地面观测网络计算的植被萌发日期之间的差异。分析了德国以落叶阔叶树为主的景观。虽然地面观测通常记录了萌芽破裂的开始，但遥感指的是可检测到的表面反射率的变化，这解释了大部分叶子的展开。卫星探测到两个信号，即使是在相同的站位上：下层变绿，不久后，树冠(上层)变绿。比较的结果表明，虽然不是一致的，但卫星产生的绿色早于地面观测得出的萌芽，我们假设这是由于不同的地面覆盖和卫星探测到的非树木植被的绿化所致。通过分析卫星观测的绿化期(d(Gu))和地面观测到的萌发期(d(Bb))在卫星场景中非落叶森林(NDF)土地利用类型比例的函数来检验这一假设。分析卫星数据(每日1公里分辨率的AVHRR产品)时，陆面要素的选择标准逐渐受到更多限制。使用高斯混合模型比较两组观测，以评估由两组产生的概率密度函数(PDF)的统计特性，而不是地理上重合的数据的比较。结果表明，异质植被覆盖很可能是决定优势树种计算的返青日期和萌发日期之间差异的主要因素。(C)2009 Elsevier Inc.保留所有权利。
The main objective of the current paper is to evaluate and explain differences between computed green-up dates of vegetated land surface derived from satellite observations and budburst dates from ground observational networks. Landscapes dominated by deciduous broad-leaved trees in Germany are analysed. While ground observations generally record the onset of bud break, remote sensing refers to a detectable change of surface reflectance, which accounts for the unfolding of the majority of the leaves. The satellite detects, even in a homogeneous stand, two signals: the green-up of the understorey and, shortly after, the green-up of the canopy (overstorey). Results of comparisons indicate an earlier, although not consistently, satellite-derived green-up than bud break derived from ground observations.We hypothesise that this is due to heterogeneous ground cover and a detection of the greening of non-tree vegetation by the satellite. This hypothesis is tested by analysing the difference between satellite-derived green-up dates (d(GU)) and budburst observed on the ground (d(BB)) in function of the proportion of non-deciduous-forest (ndf) land use types in satellite scenes. The satellite data (a daily 1-km resolution AVHRR product) are analysed with progressively more restricted selection criteria regarding the land surface elements. The two sets of observations are compared using Gaussian Mixture Models to evaluate the statistical properties of the probability density functions (pdf) as produced by the two sets rather than comparisons of geographically coincident data. It is shown that a heterogeneous vegetation cover is likely to be the main factor determining the difference between the computed green-up date and date of budburst of the dominating tree species. (C) 2009 Elsevier Inc. All rights reserved.