Linking satellite-based spring phenology to temperate deciduous broadleaf forest photosynthesis activity

Satellite-based remote sensed phenology has been widely used to assess global climate change. However, it is constrained by uncertain linkages with photosynthesis activity. Two dynamic threshold methods were employed to retrieve spring phenology metrics from four Moderate Resolution Imaging Spectroradiometer (MODIS) products, including fraction of Absorbed Photosynthetically Active Radiation (fAPAR), Leaf Area Index (LAI), Normalized Difference Vegetation Index (NDVI), and Enhanced Vegetation Index (EVI) for three temperate deciduous broadleaf forests in North America between 2001 and 2009. These MODIS-based spring phenology metrics were subsequently linked to the photosynthetic curves (daily gross primary productivity, GPP) measured by an eddy covariance flux tower. The 20% dynamic threshold spring onset metrics from MODIS products were closer to the photosynthesis onset metrics at the date of 2% GPP increase for NDVI and fAPAR, and closer to the date of 5% and 10% increase of GPP for EVI and LAI, respectively. The 50% dynamic threshold onset metrics were closer to the photosynthesis onset metrics at the date of 10% GPP increase for NDVI, and closer to the date of 20% GPP increase for fAPAR, LAI and EVI, respectively. These results can improve our knowledge on the photosynthesis activity status of remotely sensed spring phenology metrics.     

顾及框架点坐标误差的三维基准转换严密模型

框架点坐标是由观测数据通过平差得到的,不可避免地受到观测误差的影响。针对原框架和目标框架坐标均存在误差、非公共点与公共点间存在相关性,以及转换系数矩阵中仅部分元素存在误差的实际情况,提出了同时考虑框架内误差以及转换点间相关性的基准转换严密模型,该模型将公共点和非公共点联合处理,同时计算坐标转换参数和所有点的坐标转换值,推导出了新的严格坐标转换公式,该公式为传统坐标转换公式基础上增加一改正量的形式;进一步,推导了原框架和目标框架坐标的方差不一致情况下的坐标转换模型的自适应解法;最后,利用"陆态网络工程"2000个区域站的实测坐标进行坐标转换验证,结果表明,这种严密模型较传统坐标转换模型具有更高的坐标转换精度。     

先验协方差阵误差对动态Kalman滤波解的影响

分别讨论当标准Kalman滤波动力学模型的状态参数协方差阵、状态噪声的协方差阵及观测噪声的协方差阵含有误差时,对滤波结果的影响并导出相应的解式。利用GPS/INS紧组合导航系统的实测数据对上述分析进行了实验,结果表明,动力学模型信息的协方差阵和观测信息的协方差阵在滤波中具有一个理想的平衡点,该平衡点能够合理分配动力学模型信息和观测信息对滤波解的贡献,从而可以得到可靠的滤波解。     

Research Progresses and Prospect of Chimney Effect about Carbon Cycle in the Karst Cave System

There is a long history of several decades for the systemic study of global carbon cycles, and many important achievements have been obtained. However, these studies of carbon cycles in the karst area that accounts for about 10% of the entire Earth’s land area were paid attention gradually only in the past twenty. Recent researches suggest that karstification has important effects of the global carbon cycle. At present, scientists have had a very comprehensive and systemic understanding of various factors affecting the carbon cycle in the karst area, and estimated the carbon source or sink. However, unlike non karst area, there are generally many caves and fractures that have various sizes and morphologies in the karst area. These caves and fractures provide gas exchange between epikarst zone and atmosphere with a channel (as a window) in the karst area. There have been few reports about the role of the channel in the carbon cycle in the karst area. Previous studies have shown there is an obvious chimney effect in the karst cave system, which cannot be ignored. However, through the overview of the previous studies on carbon cycle of chimney effect in the karst cave system, we found that there were still many problems need to be further studied, such as the contribution of chimney effect to regional and global atmospheric CO₂; the regional differences, the seasonal changes and its reason (driving force) of chimney effect; the influences of chimney effect on the local ecosystem. With the development of modern science and technology (such as eddy covariance, large aperture scintillation and isotope), it becomes possible to solve the above problems. Therefore, it is necessary to use these advanced means for automatic and continuous monitoring and researching the carbon cycles in the karst cave system, which are of important significance for the researches of carbon cycles in the karst area, even for the global carbon cycle studies.     

生态系统碳通量估算中耦合涡度协方差与遥感技术研究进展

陆地生态系统CO^₂和水热通量的长期观测研究一直是国际上关注的热点问题。截止目前,利用微气象学原理的涡度协方差技术是唯一能直接测定生物圈与大气间物质与能量通量的标准方法,成为国际通量观测网络的主要技术。但是涡度协方差技术的测定仍然是一种小尺度观测方法,其观测结果难于直接外推到更大尺度。同时,缺乏区域、跨尺度生态系统及其时空动态观测数据一直是限制碳循环研究的主要障碍,而遥感技术的发展可望在不远的将来使大尺度、高分辨生态系统变化的长期定量观测成为可能。这些问题在当今集中体现在如何建立通量—遥感的跨尺度观测体系,并有效地将有限的通量站点测量数据与大尺度遥感资料以及生态模型有机地结合。总结过去耦合涡度协方差技术与遥感技术的工作,主要在以下3个层面展开：①涡度协方差技术与遥感技术对碳通量估算的相互验证;②涡度协方差技术为遥感反演提供地面参数;③遥感观测解译辅助分析通量贡献区（footprint）。集中在这3个方面进行探讨,通过总结各方面的研究特点与进展,可望为未来在这个领域开展工作理顺思路。     

Estimation of covariance parameters in kriging via restricted maximum likelihood

In kriging, parametric approaches to covariance (or variogram) estimation require that unknown parameters be inferred from a single realization of the underlying random field. An approach to such an estimation problem is to assume the field to be Gaussian and iteratively minimize a (restricted) negative loglikelihood over the parameter space. In doing so, the associated computational burden can be considerable. Also, it is usually not easy to check whether or not the minimum achieved is global. In this note, we show that in many practical cases, the structure of the covariance (or variogram) function can be exploited so that iterative minimizing algorithms may be advantageously replaced by a procedure that requires the computation of the roots of a simple rational function and the search for the minimum of a function depending on one variable only. As a consequence, our approach allows one to observe in a straightforward fashion the presence of local minima. Furthermore, it is shown that insensitivity of the likelihood function to changes in parameter value can be easily detected. The note concludes with numerical simulations that illustrate some key features of our estimation procedure.     

协方差函数的选择对GPS高程拟合精度的影响

阐述最小二乘配置的原理,给出先验方差协方差估计方法,通过实例分析了采用最小二乘配置法的有效性,比较了不同协方差函数对拟合精度的影响及拟合点的分布对协方差函数、拟合结果的影响。     

GIS空间数据质量控制的抗差拟合推估法

拟合推估法可用于拟合系统误差,削弱随机误差的影响,提高空间数据质量。与正常拟合推估法不同,提出了一种抗差拟合推估法以控制GIS空间数据的系统误差和异常误差的影响。在此基础上,提出了对剩余残差再拟合的思想,从而对拟合推估剩余系统误差进行控制。利用该方法,一方面可以有效地抵制系统误差的影响,另一方面又可以较好地遏制异常误差的污染。此外,对因协方差函数误差导致的信号估计偏差,也具有一定的补偿能力。最后通过实际计算与分析验证了该方法的有效性。     

冬季北太平洋风暴轴的年代际变化特征及其可能影响机制

利用1958-2002年的ERA-40再分析资料,用谐波变换和EOF方法分析了冬季北太平洋风暴轴在年代际时间尺度上的变化特征,并通过回归分析的方法初步探讨了风暴轴年代际变化的可能影响机制.结果表明,在年代际时间尺度上,北太平洋风暴轴有两种主要模态,第1模态是风暴轴在其气候平均位置增强或减弱的主体一致变化型,其年代际变化受到上游涡旋强迫的影响,北大西洋强(弱)的涡旋活动,使得冬季北太平洋西风急流减弱(增强)、变宽(窄)、北抬(南压),同期北太平洋风暴轴活动偏强(弱),黑潮延续体区海表温度有偏暖(冷)的响应;第2模态是风暴轴中东部在气候平均位置南北两侧振荡的经向异常型,与太平洋年代际振荡(PDO)循环的暖(冷)位相相联系,下垫面海温非绝热加热的作用,激发加强(减弱)大气中类太平洋/北美遥相关型(PNA)的响应,引起大气斜压性异常偏南(北),使得风暴轴整体南压(北抬),且中东部向东南(北)方向移动.因此,冬季北太平洋风暴轴的年代际变化不仅是局地波-流相互作用的结果,还应考虑上游涡旋活动和海温热力强迫的作用.     

基于等价方差-协方差阵的稳健最小二乘估计理论研究

在对现有的基于等价权的稳健估计的弊端进行分析的基础上 ,建立起一套基于调整观测量方差 -协方差阵的稳健最小二乘估计理论 ,包括相关ρ函数、相关φ函数、等价方差 -协方差函数、等价方差 -协方差因子、影响函数、崩溃污染率等。通过算例证明本文所提出的基于等价方差 -协方差的稳健估计思想、模型的正确性和可行性