Retrieval of effective leaf area index (LAIe) and leaf area density (LAD) profile at individual tree level using high density multi-return airborne LiDAR     

《International Journal of Applied Earth Observation and Geoinformation》2016

As an important canopy structure indicator, leaf area index (LAI) proved to be of considerable implications for forest ecosystem and ecological studies, and efficient techniques for accurate LAI acquisitions have long been highlighted. Airborne light detection and ranging (LiDAR), often termed as airborne laser scanning (ALS), once was extensively investigated for this task but showed limited performance due to its low sampling density. Now, ALS systems exhibit more competing capacities such as high density and multi-return sampling, and hence, people began to ask the questions like—“can ALS now work better on the task of LAI prediction?” As a re-examination, this study investigated the feasibility of LAI retrievals at the individual tree level based on high density and multi-return ALS, by directly considering the vertical distributions of laser points lying within each tree crown instead of by proposing feature variables such as quantiles involving laser point distribution modes at the plot level. The examination was operated in the case of four tree species (i.e. Picea abies, Pinus sylvestris, Populus tremula and Quercus robur) in a mixed forest, with their LAI-related reference data collected by using static terrestrial laser scanning (TLS). In light of the differences between ALS- and TLS-based LAI characterizations, the methods of voxelization of 3D scattered laser points, effective LAI (LAIe) that does not distinguish branches from canopies and unified cumulative LAI (ucLAI) that is often used to characterize the vertical profiles of crown leaf area densities (LADs) was used; then, the relationships between the ALS- and TLS-derived LAIes were determined, and so did ucLAIs. Tests indicated that the tree-level LAIes for the four tree species can be estimated based on the used airborne LiDAR (R² = 0.07, 0.26, 0.43 and 0.21, respectively) and their ucLAIs can also be derived. Overall, this study has validated the usage of the contemporary high density multi-return airborne LiDARs for LAIe and LAD profile retrievals at the individual tree level, and the contribution are of high potential for advancing forest ecosystem modeling and ecological understanding.  相似文献   

Method for evaluating the degrees of land use sustainability of mountainous county and its application in Yunnan Province,China   总被引：4，自引：1，他引：3  

Zisheng Yang  Yansui Liu  Wenxing Tao  Jingjing Xu  Qiaogui Zhao 《山地科学学报》2008,5(2):98-112

The evaluation of sustainable land use is the key issue in the field of studying the sustainable land utilization. In general analysis, the sustainable land use is evaluated respectively from its ecological sustainability, economic sustainability and social sustainability in China and other countries in recent years. Although this evaluation is an important work, it seems insufficient and hard to comprehensively reflect the whole degree of land use sustainability. Thus, to make up this deficiency, this paper brings forward the evaluation indexes, which make it possible to quantitatively reflect the whole degree of land use sustainability, namely, the concept of ＂degrees of overall land use sustainability＂ （Dos）, and research and measurement development of the method of and calculation in Dos. Taking the evaluation of the degree of land use sustainability in county regions of Yunnan Province as the actual example for analysis, results are basically as follows：
1） The degree of land use sustainability （Dos） is the ration index to organically and systematically integrate the degree of ecological friendliness （DeF）, the degree of economic viability （Dev） and the degree of social acceptability （Dsa）, able to comprehensively reflect the whole sustainability degree of regional land use
2） Based on the value of Dos, the grading system and standard for the sustainability of land use may be established and totally divided into five grades, namely, the high-degree sustainability, middle-degree sustainability, low-degree sustainability, conditional sustainability and non-sustainability. Meanwhile, the standard for distinguishing sustainability grades has also been confirmed so as to determine the nature of sustainability degrees in different grades. This makes the possibility for the combination of nature determination with ration in research result and provides with the scientific guideline and decision-making gist for better implementation of sustainable land use strategy.
3） The pract  相似文献   

Wet and Dry Basalt Magma Evolution at Torishima Volcano, Izu Bonin Arc, Japan: the Possible Role of Phengite in the Downgoing Slab   总被引：1，自引：0，他引：1  

Tamura  Y.; Tani  K.; Chang  Q.; Shukuno  H.; Kawabata  H.; Ishizuka  O.; Fiske  R. S. 《Journal of Petrology》2007,48(10):1999-2031

The arc-front volcanoes of Sumisu (31·5°N, 140°E)and Torishima (30·5°N, 140·3°E) in thecentral Izu–Bonin arc are similar in size and rise asrelatively isolated edifices from the seafloor. Together theyprovide valuable along-arc information about magma generationprocesses. The volcanoes have erupted low-K basalts originatingfrom both wet and dry parental basaltic magmas (low-Zr basaltsand high-Zr basalts, respectively). Based on models involvingfluid-immobile incompatible element ratios (La/Sm), the parentalbasalts appear to result from different degrees of partial meltingof the same source mantle (20% and 10% for wet and dry basaltmagmas, respectively). Assuming that the wet basalts containgreater abundances of slab-derived components than their drycounterparts, geochemical comparison of these two basalt typespermits the identification of the specific elements involvedin fluid transport from the subducting slab. Using an extensiveset of new geochemical data from Torishima, where the top ofthe downgoing slab is about 100 km deep, we find that Cs, Pb,and Sr are variably enriched in the low-Zr basalts, which cannotbe accounted for by fractional crystallization or by differencesin the degree of mantle melting. These elements are interpretedto be selectively concentrated in slab-derived metasomatic fluids.Variations in K, high field strength element and rare earthelement concentrations are readily explained by variations inthe degree of melting between the low- and high-Zr basalts;these elements are not contained in the slab-derived fluids.Rb and Ba exhibit variable behaviour in the low-Zr basalts,ranging from immobile, similar to K, to mildly enriched in somelow-Zr basalts. We suggest that the K-rich mica, phengite, playsan important role in determining the composition of fluids releasedfrom the downgoing slab. In arc-front settings, where slab depthis 100 km, phengite is stable, and the fluids released fromthe slab contain little K. In back-arc settings, however, wherethe slab is at 100–140 km depth, phengite is unstable,and K-rich fluids are released. We conclude that cross-arc variationsin the K content of arc basalts are probably related to differingcompositions of released fluids or melts rather than the widelyheld view that such variations are controlled by the degreeof partial melting. KEY WORDS: arc volcano; degrees of melting; mantle wedge; water; wet and dry basalts  相似文献   

Evaluating assumptions for seismic assessment of existing buildings     

V.G. Bardakis  S.E. Dritsos   《Soil Dynamics and Earthquake Engineering》2007,27(3):223-233

This paper evaluates the American FEMA 356 and the Greek GRECO (EC 8 based) procedural assumptions for the assessment of the seismic capacity of existing buildings via pushover analyses. Available experimental results from a four-storeyed building are used to compare the two different sets of assumptions. If the comparison is performed in terms of initial stiffness or plastic deformation capacities, the different partial assumptions of the procedures lead to large discrepancies, while the opposite occurs when the comparison is performed in terms of structural performance levels at target displacements. According to FEMA 356 assumptions, effective yield point rigidities are approximately four times greater than those of EC 8. Both procedures predicted that the structure would behave elastically during low-level excitation and that the structural performance level at target displacement for a high-level excitation would be between the Immediate Occupancy and Life Safety performance levels.  相似文献   

云顶以下臭氧对TOMS反演臭氧总量的影响及反演方法的理论研究   总被引：4，自引：2，他引：4       下载免费PDF全文

江芳  王英鉴  刘振兴  王咏梅  张晓庆 《地球物理学报》2007,50(2):364-369

目前紫外后向散射反演臭氧总量的所有算法，都将云考虑成不透明的Lambertian反射体，并假定云顶有效反照率不随波长的变化而变化.然而本文通过模拟计算发现，由于云散射、瑞利散射、臭氧吸收三种作用的综合结果，云顶的有效反照率是与波长相关的，即使光学厚度比较大的云，辐射也可由云顶继续向下传输，因而会受到云顶以下臭氧吸收的影响.用V7方法进行反演，模拟计算结果表明：云的出现使得云顶以下，特别是云内光程增强，导致紫外波段的臭氧吸收衰减增大，所以反演出的臭氧总量值比真实值偏大，本文称这种现象为“云吸收效应”，并讨论了该效应的影响因子.最后，在辐射传输模拟的基础上建立一套反演算法，大大减弱了“云吸收效应”的影响.  相似文献   

有机质热演化过程中地层压力的作用与影响     

王兆明  罗晓容  陈瑞银  宋海明  周波  郑大海 《地球科学进展》2006,21(1):39-48

压力对有机质演化的影响长期以来争论不断，共有3种不同意见：压力对有机质演化没有影响，压力促进有机质的演化，压力抑制有机质的演化。通过对前人所做实验的实验设备、实验样品及实验结果的分析对比发现：不同实验结果主要是由于不同实验条件引起的，特别是实验系统和加压方式的不同，对实验结果影响最大，所代表的地质意义也不同。综合分析结果表明，当压力的增加表现为沉积有机质受到的有效应力增加时可以促进有机质生烃；当压力的增加表现为孔隙流体压力增加时，有机质生烃过程将受到抑制；另外，这两种情况都可能使干酪根的镜质组反射率降低，易使人得出压力增加抑制有机质演化的结论。进一步对压力影响有机质演化的成因机制进行了分析，发现在有机质演化的不同阶段因异常压力的增压机制不同，压力在有机质演化过程中所表现出来的作用也有差异。  相似文献   

Upscaling: Effective Medium Theory, Numerical Methods and the Fractal Dream     

Y. Guéguen  M. Le Ravalec  L. Ricard 《Pure and Applied Geophysics》2006,163(5-6):1175-1192

Upscaling is a major issue regarding mechanical and transport properties of rocks. This paper examines three issues relative to upscaling. The first one is a brief overview of Effective Medium Theory (EMT), which is a key tool to predict average rock properties at a macroscopic scale in the case of a statistically homogeneous medium. EMT is of particular interest in the calculation of elastic properties. As discussed in this paper, EMT can thus provide a possible way to perform upscaling, although it is by no means the only one, and in particular it is irrelevant if the medium does not adhere to statistical homogeneity. This last circumstance is examined in part two of the paper. We focus on the example of constructing a hydrocarbon reservoir model. Such a construction is a required step in the process of making reasonable predictions for oil production. Taking into account rock permeability, lithological units and various structural discontinuities at different scales is part of this construction. The result is that stochastic reservoir models are built that rely on various numerical upscaling methods. These methods are reviewed. They provide techniques which make it possible to deal with upscaling on a general basis. Finally, a last case in which upscaling is trivial is considered in the third part of the paper. This is the fractal case. Fractal models have become popular precisely because they are free of the assumption of statistical homogeneity and yet do not involve numerical methods. It is suggested that using a physical criterion as a means to discriminate whether fractality is a dream or reality would be more satisfactory than relying on a limited data set alone.  相似文献   

运用价格杠杆,实现水资源有效控制   总被引：4，自引：0，他引：4  

苏宝军 《地下水》2003,25(3):129-130

合理的水价形成机制是实现水利工程良性运行的必然要求，是实现对水资源可持续利用、保障经济社会可持续发展的现实需要，是实现水资源优化配置、建立节水型社会的重要保障。本文对如何推进水价改革，发挥水价在水资源开发利用中的杠杆作用，实现对水资源的有效控制进行了探讨。  相似文献   

Paleoclimate reconstruction based on the timing of speleothem growth and oxygen and carbon isotope composition in a cave located in the rain shadow in Israel     

Anton VaksMiryam Bar-Matthews  Avner AyalonBettina Schilman  Mabs GilmourChris J Hawkesworth  Amos FrumkinAaron Kaufman  Alan Matthews 《Quaternary Research》2003,59(2):182-193

High-resolution ²³⁰Th/²³⁴U ages and δ¹⁸O and δ¹³C compositions of speleothems in Ma’ale Efrayim Cave located to the east of the central mountain ridge of Israel enable us to examine the nature of the rain shadow aridity during glacial and interglacial intervals. Speleothem growth occurred during marine glacial isotopic periods, with no growth during the two last marine isotope interglacial intervals and during the peak of the Last Glacial Maximum. This contrasts with speleothem growth in caves located on the western flank of the central mountain ridge, in the Eastern Mediterranean semiarid climatic zone, which continued throughout the last 240,000 yr. Thus, during glacial periods water reached both sides of the central mountain ridge. A comparison of the present-day rain and cave water isotopic compositions and amounts at the Ma’ale Efrayim Cave site with those on the western flank shows that evaporation and higher temperatures on the eastern flank are major influences on isotopic composition and the lack of rainfall. The δ¹⁸O and δ¹³C profiles of the speleothems deposited between 67,000 and 25,000 yr B.P. match the general trends of the isotopic profiles of Soreq Cave speleothems, suggesting a similar source (eastern Mediterranean Sea) and similar climatic conditions. Thus, during glacial periods the desert boundary effectively migrated further south or east from its present-day location on the eastern flank, whereas interglacial periods appear to have been similar to the present, with the desert boundary at the same position. The decrease in overall temperature and a consequent reduction in the evaporation to precipitation ratios on the eastern flank are viewed as the major factors controlling the decay of the rain shadow effect during glacial periods.  相似文献   

天球有效大气角动量中的周年和半年项估计     

黄乘利  廖新浩  朱耀仲  金文敬 《测绘学报》2000,29(Z1):70-74

为了讨论大气对非刚体地球章动周年和半年项的贡献,本文将大气有效角动量(1980.0～1998.33)从地面参考系转换至空间参考系得到大气的天球有效角动量CEAM,低通滤波后用最小二乘方法拟合得到顺、逆向周年和半年项的振幅估计。  相似文献