激光高度计卫星ICESAT在地学研究中的应用

介绍了世界首颗激光高度计卫星ICESat及其惟一有效的载荷——地学激光测高系统(GLAS)以及它的科学研究目的和工作原理,论述了ICESat在地学研究中的应用。     

Digital system for recording fish echoes

A system to record digitised echo information from echo sounders has been developed as part of a project to improve methods of estimating the abundance of fish stocks around New Zealand. The depth of echoes appearing at the echo‐sounder receiver is determined, followed by a sequence of samples of the echo envelope defining its shape. All data are digitised and recorded on a seven‐track digital magnetic tape recorder. The system is designed to preserve as much information about the echoes as possible. In contrast to other published systems designed to either “count” or “integrate” fish echoes, this system allows free choice of methods of analysis.     

城市形象研究进展及展望

城市形象体现了一个城市的文化特征和城市精神,在当前全球化背景下,已经成为城市的一种重要竞争力,城市形象的好坏对于城市的社会经济发展具有重大影响。从城市形象的理论和实证两部分研究内容出发,系统阐述了当前理论所包含的研究内容及对实证研究区域进行统计分析,并实证分析中国19个省、自治区,81个县、市的城市形象定位,指出当前国内在城市形象研究内容、研究区域及研究方法上存在的不足,以其为中国城市形象研究提供参考。     

一种基于面积平衡约束的图斑化简算法

保持综合前后各地类土地面积平衡是土地利用数据综合的基本原则.地类图斑是面积统计的最小单元,用常规的线化简算法不但难以保证图斑的地理特性,而且会给面积统计带来不确定性.该文提出一种能够使图斑化简前后面积保持绝对平衡的化简算法,该算法给出了求取图斑群和岛图斑的地理特征点、几何特征点的相关方法,对被特征点分割的综合子弧段运用直线面积平衡和参数曲线面积平衡两种求取平衡线的方式进行化简,基本原理是综合前后弧段切割它们自身的包络矩形面积比相等,且综合后的弧段须落入综合前子弧段的误差缓冲区内.实验表明,该算法不但能保持图斑的形态特征,而且能保持图斑化简前后面积绝对相等.     

基于能量平衡法的原状冻土Ⅰ型非线性断裂韧度测试研究

基于能量平衡的原理,采用冻土弯曲断裂试验模型,根据不同深度的冻胀量、冻深与时间变化规律,严格控制试样制作及试验时的温度,对原状冻土进行了断裂韧度测试试验。得出Ⅰ型直裂纹试样的 和 值,从而为原状冻土的非线性断裂破坏问题的研究进行了有意义的尝试,拓宽了思路。     

基于城市功能分区的碳收支平衡时空分异研究

研究城市主导功能影响下区域碳平衡时空分异,有助于理解城市功能格局与碳循环过程之间的作用机制。本研究以厦门市6个区为例,采用各区历史统计数据以及卫星影像处理的土地利用数据,通过构建简化的区域碳收支计算模型,核算各行政区不同历史时期的碳平衡,结果表明：厦门市整体上呈现碳收支失衡逐渐加剧的趋势,2003年CO₂排放量是吸收量的1.91倍,2013年增长至7.44倍;各区碳代谢以及碳平衡表现出不同的时空分异特征。结合厦门市城市建设总体规划中制订的主导功能分类,阐明主导功能影响下时空分异的社会经济、自然景观等驱动因素对城市碳平衡时空变化的影响机制与过程。在此基础上针对各区不同的碳平衡状况,制订适应各自主导功能的减排以及碳补偿政策。研究有助于直接服务城市的规划和建设实践,从城市生态服务角度指导建设规划,合理城市功能分区。     

Amplification system for concentrated and distributed energy dissipation devices

Recent analytic, experimental, and practical studies are developing energy dissipation devices combined with amplifying mechanisms (AM) to enhance structural behavior. This research presents the theoretical and experimental development of the eccentric lever‐arm system (ELAS), a new system generically called amplified added damping (AAD), which is a combination of an AM with one or more dampers capable of supporting large deformations. The proposed AM device is a variant of the well‐known lever‐arm system. This work is divided in four parts: (1) kinematics of the ELAS and definition of an equivalent AAD; (2) parametric analysis of a linear single‐story structure with ELAS; (3) numerical analysis of a multi‐degree‐of‐freedom structure with frictional damping with and without AM; and (4) pseudo‐dynamic tests of a full scale asymmetric one story steel structure with and without frictional AAD. Parametric analyses demonstrate that using high‐amplification ratios and low supplemental damping could be a good practice. On the other hand, similar to systems without AMs, dissipation efficiency increases conformably with the stiffness of the secondary structure. As expected, it was observed that deformation was highly concentrated in the flexible edge of the asymmetric test model without damper. Conversely, the structure with frictional AAD clearly showed uniform plane deformation. The implemented AM, which has a large amplifying ratio of α≈11, performed with close accordance with numerical simulations and a high mechanical efficiency (≈95%) using a frictional damper with a very low force capacity. Copyright © 2016 John Wiley & Sons, Ltd.     

Denudation intensity and control in the Chinese Tian Shan: new constraints from mass balance on catchment‐alluvial fan systems

Tectonics and climate are usually seen as the main controlling factors of denudation rates, which seem to rise with the tectonic activity and to decrease when the climate becomes drier. However, the low denudation rates observed in semi‐arid to arid contexts are generally measured on orogenic plateaus where the respective influence of the flat relief and the dry climate cannot really be unravelled. The Chinese Tian Shan was chosen as a case study. In the northern piedmont of this mountain range, a series of well‐preserved Quaternary alluvial fans offer the opportunity to perform a mass balance study at the scale of several catchment areas and several hundreds of thousands of years. Based on a geometrical reconstruction of these fans, the volumes of sediments exported out of 10 drainage basins during the Middle–Late Pleistocene (from ～300 to ～12 kyr) and the Holocene (from ～12 kyr to present) have been estimated. From these volumes, an average denudation rate of ～135 m/Myr was determined in the Tian Shan Range for the last 300 kyr. In agreement with other mass balances performed in the same area, the typical denudation intensity of the northern Tian Shan is thus of a few hundred meters per million years at most, regardless of the space and time scales considered. From a comparison with denudation rates in other mountain ranges throughout the world, we suggest that a dry climate can dramatically limit the denudation intensity even in active orogenic systems with a high topographic gradient like the Tian Shan. As a result, the time required to reach equilibrium between denudation and rock uplift in these systems could be extremely long (i.e. of more than several million years). Copyright © 2016 John Wiley & Sons, Ltd.     

Spatial distribution of surface energy fluxes over the Loess Plateau in China and its relationship with climate and the environment

China's Loess Plateau is located at the edge of the Asian summer monsoon in a transition zone of climate and ecology. In the Loess Plateau, climate and environments change along with space, which has an obvious impact on the spatial distribution of surface energy fluxes. Because of scarce land-surface observation sites and short observation time in this area, previous studies have failed to fully understand the land-surface energy balance characteristics over the entire the Loess Plateau and their effect mechanisms. In this paper, we first test the simulation ability of the Community Land Model(CLM) model by comparing its simulated data with observed data. Based on the simulation data for the Loess Plateau over the past thirty years, we then analyze the spatial distribution of surface energy fluxes and compare the pattern differences between the area averages for the driest year and wettest year. Furthermore, we analyze the relationship between the spatial distribution of the components of the surface energy balance with longitude, latitude, altitude, precipitation and temperature. The main results are as follows: the spatial distribution of surface energy fluxes are significantly different, with the surface net radiation and sensible heat flux increasing from south to north and latent heat flux and soil heat flux decreasing from southeast to northwest. The sensible heat flux at the driest point is nearly twice as high as that at the wettest point, whereas the latent heat flux and soil heat flux at the driest point are half as much as that at the wettest point. The impact of variations of annual precipitation on the components of the surface energy balance is also obvious, and the maximum magnitude of the changes to the sensible heat flux and latent heat flux is nearly 30%. To a certain extent, geographical factors(including longitude, latitude, and altitude) and climate factors(including temperature and precipitation) affect the surface energy fluxes. However, the surface net radiation is more closely related to latitude and altitude, sensible heat flux is more closely related to the monsoon rainfall and latitude, and latent heat flux and soil heat flux are more closely related to the monsoon rainfall.     

Enhanced modeling of latent heat flux from urban surfaces in the Noah/single-layer urban canopy coupled model

The numerical modeling of the impacts of urban buildings in mesoscale meteorological models has gradually improved in recent years. Correctly representing the latent heat flux from urban surfaces is a key issue in urban land-atmosphere coupling studies but is a common weakness in current urban canopy models. Using the surface energy balance data at a height of 140 m from a 325 m meteorological tower in Beijing, we conducted a 1-year continuous off-line simulation by using a coupled land surface model and a single-layer urban canopy model and found that this model has a relatively large systematic error for simulated latent heat flux. To improve the numerical method for modeling latent heat flux from urban surfaces, we combined observational analysis and urban land surface model to derive an oasis effect coefficient for urban green areas; to develop a temporal variation formula for water availability in urban impervious surfaces; and to specify a diurnal profile and the maximum values of anthropogenic latent heat release for four seasons. These results are directly incorporated into the urban land surface model to improve model performance. In addition, this method serves as a reference for studies in other urban areas.