陕北榆林地区土地覆被变化分析

基于1981~2001 年NOVAA/AVHRR 和1998~2004 年SPOT VEGETATION 归一化植被 指数(NDVI) 数据, 对榆林地区植被动态变化进了定量研究, 并且利用多年气象数据分析了降水 和温度变化情况。结果表明: 榆林地区植被有了明显改善, 其改善状况集中于8、9、10 月份; 植被 覆被变化具有明显的区域差异, 北部植被覆盖改善的趋势明显, 且变化比较平稳; 南部增加趋势 不明显, 有的地方还呈下降趋势, 变化幅度大。     

数字经济发展对城市碳排放影响的空间效应

为探讨数字经济对城市碳排放影响的空间效应,基于2011—2017年286个城市面板数据综合测度数字经济发展水平,运用空间杜宾模型及空间DID模型分析数字经济发展对城市碳排放的影响。主要得到以下结论：① 数字经济发展存在明显的空间异质性,发展格局从“多点式”零星分布向“组团式”聚集形态转变,但各城市发展层级差距仍未改善,长三角成为重要的数字经济高水平集聚区。② 数字经济发展显著改善了城市碳排放,通过引入“智慧城市”这一外生政策冲击进行检验,发现结论具有稳健性,而且这种效应存在明显的空间异质性,东部地区数字经济发展对碳排放的负向影响作用较强,位于城市群内部的区域受数字经济的影响更大。③ 数字经济发展对碳排放的作用在不同经济圈层内有所差异,空间外溢具有边界效应,在1100km处外溢达到峰值。④ 数字产业发展、数字创新能力以及数字普惠金融是数字经济影响城市碳排放效应发挥的重要因素。     

1982-2006年中国东部春季植被变化(英文)

Vegetation greenness is a key indicator of terrestrial vegetation activity. To under-stand the variation in vegetation activity in spring across eastern China (EC), we analysed the variation in the Normalised Difference Vegetation Index (NDVI) from April to May during 1982-2006. The regional mean NDVI across EC increased at the rate of 0.02/10yr (r2=0.28; p=0.024) prior to 1998; the increase ceased, and the NDVI dropped to a low level thereafter. However, the processes of variation in the NDVI were different from one region to another. In the North China Plain, a cultivated area, the NDVI increased (0.03/10yr; r2=0.52; p<0.001) from 1982 to 2006. In contrast, the NDVI decreased (-0.02/10yr; r2=0.24; p=0.014) consecu-tively from 1982 to 2006 in the Yangtze River and Pearl River deltas, two regions of rapid urbanisation. In the eastern region of the Inner Mongolian Plateau and the lower reaches of the Yangtze River in East China, the NDVI increased prior to 1998 and decreased thereafter. In the Hulun Buir area and the southern part of the Yangtze River Basin, the NDVI increased prior to 1998 and remained static thereafter. The NDVI in the grasslands and croplands in the semi-humid and semi-arid areas showed a significant positive correlation with precipitation, while the NDVI in the woodlands in the humid to semi-humid areas showed a significant positive correlation with temperature. As much as 60% of the variation in the NDVI was ex-plained by either precipitation or temperature.     

Numerical modelling of stream–aquifer interaction: Quantifying the impact of transient streambed permeability and aquifer heterogeneity

Stream–aquifer interaction plays a vital role in the water cycle, and a proper study of this interaction is needed for understanding groundwater recharge, contaminants migration, and for managing surface water and groundwater resources. A model‐based investigation of a field experiment in a riparian zone of the Schwarzbach river, a tributary of the Rhine River in Germany, was conducted to understand stream–aquifer interaction under alternative gaining and losing streamflow conditions. An equivalent streambed permeability, estimated by inverting aquifer responses to flood waves, shows that streambed permeability increased during infiltration of stream water to aquifer and decreased during exfiltration. Aquifer permeability realizations generated by multiple‐point geostatistics exhibit a high degree of heterogeneity and anisotropy. A coupled surface water groundwater flow model was developed incorporating the time‐varying streambed permeability and heterogeneous aquifer permeability realizations. The model was able to reproduce varying pressure heads at two observation wells near the stream over a period of 55 days. A Monte Carlo analysis was also carried out to simulate groundwater flow, its age distribution, and the release of a hypothetical wastewater plume into the aquifer from the stream. Results of this uncertainty analysis suggest (a) stream–aquifer exchange flux during the infiltration periods was constrained by aquifer permeability; (b) during exfiltration, this flux was constrained by the reduced streambed permeability; (c) the effect of temporally variable streambed permeability and aquifer heterogeneity were found important to improve the accurate capture of the uncertainty; and (d) probabilistic infiltration paths in the aquifer reveal that such pathways and the associated prediction of the extent of the contaminant plume are highly dependent on aquifer heterogeneity.     

The Backus–Gilbert approach to the 3-D structure in the upper mantle – II. SH and SV velocity

Summary. Phase velocity variations obtained in the previous paper are inverted by the Backus–Gilbert method for the velocity structure of the upper mantle. Spheroidal modes and toroidal modes in the period range of 125–260 s are used in the inversion. The data cannot constrain all six parameters in a transversely isotropic medium and we chose to perturb only two parameters, SH and SV velocities. SV velocities are resolved between the depths of about 200 and 400 km and SH velocities between 0 and 200 km. Resolution kernels have half-peak widths of about 200–300 km in depth, becoming broader for deeper target depths. SV velocity kernels show secondary peaks near the surface of the Earth, with widths varying from 50 to 100 km. The deeper the target depths, the wider the secondary peaks near the surface. SH velocity kernels do not possess such secondary peaks. The trade-off between SV and SH velocities is small. SV velocity is essentially determined by spheroidal modes and SH velocity by toroidal modes. Because of the broad width of the resolution kernels, the structure in the resolved region is difficult to detect from our data set; for example the differences in SV velocity structure between 250 and 350 km or the differences in SH velocity between 100 and 200 km are difficult to distinguish. Considering the horizontal resolution of about 2000 km, obtained in the previous paper, averaging kernels for 3-D structure are quite elongated in the horizontal dimension.     

Multi-level temporal autoregressive modelling of daily activity satisfaction using GPS-integrated activity diary data

In this research, we match web-based activity diary data with daily mobility information recorded by GPS trackers for a sample of 709 residents in a 7-day survey in Beijing in 2012 to investigate activity satisfaction. Given the complications arising from the irregular time intervals of GPS-integrated diary data and the associated complex dependency structure, a direct application of standard (spatial) panel data econometric approaches is inappropriate. This study develops a multi-level temporal autoregressive modelling approach to analyse such data, which conceptualises time as continuous and examines sequential correlations via a time or space-time weights matrix. Moreover, we manage to simultaneously model individual heterogeneity through the inclusion of individual random effects, which can be treated flexibly either as independent or dependent. Bayesian Markov chain Monte Carlo (MCMC) algorithms are developed for model implementation. Positive sequential correlations and individual heterogeneity effects are both found to be statistically significant. Geographical contextual characteristics of sites where activities take place are significantly associated with daily activity satisfaction, controlling for a range of situational characteristics and individual socio-demographic attributes. Apart from the conceivable urban planning and development implications of our study, we demonstrate a novel statistical methodology for analysing semantic GPS trajectory data in general.     

多模型协同下的城郊地区DEM构建方法研究

人类活动对地表的改造使其呈现形态多样化、不连续等特征,此时传统的DEM构建方法难以满足这些区域DEM精度要求。为此,本文提出了一种多模型协同构建DEM的思路,首先按照形态特征和语义信息对地形进行分类,然后对不同类型的地形区域,选择、设计适宜的方法分别进行DEM构建,最后将不同区域构建DEM结果融合拼接形成区域完整的DEM结果。本文选择江苏省南京市城市郊区某区域为实验区,以1:500比例尺地形图为基本数据源进行DEM构建实验。实验结果表明,与传统经典DEM构建方法相比,本文提出的多模型协同的DEM构建方法能够有效表达实验区域不同的地形特征,特别是对于人工改造的地形(如道路、边坡等区域),本文方法构建的DEM其形态精度优势显著;同时,基于验证点法的高程精度分析结果表明,本文方法构建DEM的高程精度亦优于传统DEM构建方法,特别是对于一些形态规则而高程信息相对稀少的区域,以边坡区域为例,经典DEM构建法平均误差均超过5 m,而本文构建结果平均误差为0.26 m,精度优势非常明显。研究表明本文提出的多模型协同的DEM构建方法适用于人类活动改造或显著影响的区域的DEM构建。     

Thermodynamic mixing behavior of synthetic Ca-Tschermak–diopside pyroxene solid solutions: III. An analysis of IR line broadening and heat of mixing behavior

A series of synthetic Ca-Tschermak–diopside (CaAlAlSiO₆–CaMgSi₂O₆) clinopyroxenes were investigated by powder infrared spectroscopy at room temperature in the wavenumber range 80–2,000 cm⁻¹. Measurable local structural heterogeneities in the crystals are suggested by the line broadening parameter, Δcorr that are observed for intermediate solid-solution compositions. The broadening is most pronounced in the high wavenumber region of the IR spectra that contains stretching modes involving the TO₄ polyhedra. The effective line widths for three selected wavenumber regions deviate positively from linear behavior. This is also observed for the enthalpy of mixing of this solid solution. The relationship between “excess Δcorr”, δΔcorr, and heat of mixing, ΔH _mix, behavior was investigated for this clinopyroxene series and for several other binary silicate solid solutions. The ΔH _mix versus δΔcorr slope values show a linear relationship with respect to the integrated excess volume of the various solid solutions.