Angular resolution of terrestrial laser scanners

Knowledge of a laser scanner's spatial resolution is necessary in order to prevent aliasing and estimate the level of detail that can be resolved from a scanned point cloud. Spatial resolution can be decoupled into range and angular components. The latter is the focus of this paper and is governed primarily by sampling interval and laser beamwidth. However, emphasis is often placed on one of these—typically sampling interval—as an indicator of resolution. Since both affect the resolution of a scanned point cloud, consideration of only one factor independent of the other can lead to a misunderstanding of a system's capabilities. This will be demonstrated to be inappropriate except under very specific conditions. A new, more appropriate resolution measure for laser scanners, the effective instantaneous field of view (EIFOV), is proposed. It is derived by modelling the shift variance of the equal angular increment sampling process, laser beamwidth-induced positional uncertainty and observed angle quantisation with ensemble average modulation transfer functions (AMTFs). Several commercially available terrestrial laser scanner systems are modelled and analysed in terms of their angular resolution capabilities using the EIFOV.     

洪涝统计方法探讨

利用深圳气象台1953--2005年的雨量资料，对洪涝的两种统计方法进行了对比分析，并引出了更为科学和合理的“任意连续10d／20d雨量统计洪涝的方法”。通过检验，该方法能够较准确地反映洪涝灾害的实际情况。     

Comparison of the spatial distribution of ground motion between main shocks and strong aftershocks

Using the ground motion attenuation relation, we calculated and compared the effective peak acceleration (EPA) generated by main shocks and their strong aftershocks of 21 earthquake sequences with MS≥7 occurred in Chinese mainland and offing of China during 1966~2002. The result shows that EPA of strong aftershocks usually exceed that of main shock for 76.2% earthquake sequences and EPA of more than 50% strong aftershocks are greatly lar-ger than that of main shocks in large area, which suggests that it is necessary to take damage produced by strong aftershock into account in the probabilistic seismic hazard analysis and the seismic design.     

云南省岩溶水地球物理探测实践

由于岩溶发育的不均匀性,决定了岩溶水的埋藏分布也具有不均匀的特征,含水层富水性的空间差异极大。岩溶水的不均匀性给岩溶水勘查和开发工作带来了很大的困难,以至于裸露型岩溶石山区的供水勘探孔成井率仍然很低。要有效地发挥岩溶水资源的优     

Geochemistry of overbank and high-order stream sediments in Belgium and Luxembourg: a way to assess environmental pollution

A geochemical survey of Belgium and Luxembourg was carried out as part of an international research project entitled ‘Regional geochemical mapping of Western Europe towards the year 2000'. The aim of this research was to map regional background geochemical patterns based on pristine or at least pre-industrial overbank samples and to deduce regional information on the degree of environmental pollution of floodplain and present-day river sediments. Over the entire study area (about 33,000 km²), 66 overbank sites have been sampled. Catchment areas range between 60 and 600 km². At each site an overbank profile has been dug out in the immediate vicinity of the river and described in detail. A first composite sample was taken 5–25 cm below the surface. This sample is supposed to represent deposition over the last centuries. Human interferences in this interval are often inferable based on changed sedimentary characteristics and the presence of anthropogenic particles such as charcoal, slags and brick fragments. A second composite sample was taken at depth, usually >1.5 m below the surface over an interval of about 20 cm. In most sites, the profile characteristics allowed to assume pre-industrial or even pristine conditions for this lower overbank sample. In some profiles this was confirmed by ¹⁴C-dating and/or by the absence of anthropogenic particles. Finally, a present-day stream sediment was sampled on the site to infer the actual pollution status. After drying at 80°C, disaggregation and sieving, the <125 μm fractions of the three sediment samples were analysed by XRF for major elements and several trace elements. Lower overbank samples generally show a direct link with the geological substrate and allow to assess natural background concentrations. Results from the mapping exercise as well as from the statistical analyses display a clear contrast between the northern part of Belgium where Cenozoic unconsolidated sandy and silty formations dominate which are especially vulnerable for erosion, and the southern part of Belgium and Luxembourg where Paleozoic and Mesozoic sandstones, carbonates, marls and shales are the prevalent lithologies. Here the shales are the most intensively eroded lithologies. This is especially reflected in the element patterns of Al₂O₃, MgO, K₂O, Ga, Ni, Rb, Sc and V which negatively correlate with SiO₂. Despite the human related pollution, the geological contrast between north and south Belgium is still recognisable in the geochemical pattern of the upper overbank and present-day stream sediment samples for the above-mentioned elements. Furthermore there is a clear increase in heavy metal contents (Zn, Cd, Pb, Cu), As and in certain locations in Ba from the lower to the upper overbank sediment, as well as to the present-day stream sediment. The relative increase in element content allows to assess the degree of pollution and helps to define those drainage areas where more detailed research is needed.     

平面裂隙参数计算及其对浆液流动的影响分析

利用从层流到紊流的多阶段稳定压水试验的压力－流量曲线反算裂隙张开度、粗糙度及地下水影响半径等裂隙参数。建立了平面裂隙中浆液流动的力学模型,并分析了对浆液流动的影响因素。     

Determination of characteristics of steam reservoirs by Radon-222 measurements in geothermal fluids

The authors conducted a Rn²²² survey in wells of the Larderello geothermal field (Italy) and observed considerable variations in concentrations. Simple models show that flow-rate plays an important part in the Rn²²² content of each well, as it directly affects the fluid transit time in the reservoirs. Rn²²² has been sampled from two wells of the Serrazzano area during flow-rate drawdown tests. The apparent volume of the steam reservoir of each of these two wells has been estimated from the Rn²²² concentration versus flow-rate curves.List of symbols Q Flow-rate (kg h^–1) - Decay constant of Rn²²² (=7.553×10^–3 h^–1) - Porosity of the reservoir (volume of fluid/volume of rock) - ₁ Density of the fluid in the reservoir (kg m^–3) - ₂ Density of the rock in the reservoir (kg m^–3) - M Stationary mass of fluid filling the reservoir (kg). - E Emanating power of the rock in the reservoir (nCi kg _rock ^–1 h^–1). - P Production rate of Rn²²² in the reservoir: number of atoms of Rn²²² (divided by 1.764×10⁷) transferred by the rock to the mass unit of fluid per unit time (nCi kg _fluid ^–1 h^–1). - N Specific concentration of Rn²²² in the fluid (nCi kg^–1) - Characteristic time of the steam reservoir at maximum flow-rate (=M/Q)     

A Three-year Study of Nonmethane Hydrocarbons in Surface Air over Saxony (Germany)

Measurements of the nonmethane hydrocarbon (NMHC) mixing ratio over a period of 42 months were carried out for the first time in the air of a research station situated in the former East Germany during the SANA project. Apart from four species, all other species analysed showed a statistically significant downward trend at the 95% significance level. The decrease of the hydrocarbon concentrations was superimposed by seasonal variations. A drop of about 40% of the annual mean values from 1993 to 1995 was observed. This development reflects the dramatic changes in traffic, industry, power economy, and agriculture in Saxony after the reunification of Germany. The remove of two-stroke engined cars is reflected in NMHC mixing ratio changes, as is the removal of obsolete chemical plants. Generally it was not possible to relate causes and effects of a single event, but in some cases major changes in concentrations and NMHC ratios occurred coincidentally with the disappearance of a specific emission source.     

ACMEG‐TS: A constitutive model for unsaturated soils under non‐isothermal conditions

This paper introduces an unconventional constitutive model for soils, which deals with a unified thermo‐mechanical modelling for unsaturated soils. The relevant temperature and suction effects are studied in light of elasto‐plasticity. A generalized effective stress framework is adopted, which includes a number of intrinsic thermo‐hydro‐mechanical connections, to represent the stress state in the soil. Two coupled constitutive aspects are used to fully describe the non‐isothermal behaviour. The mechanical constitutive part is built on the concepts of bounding surface theory and multi‐mechanism plasticity, whereas water retention characteristics are described using elasto‐plasticity to reproduce the hysteretic response and the effect of temperature and dry density on retention properties. The theoretical formulation is supported by comparisons with experimental results on two compacted clays. Copyright © 2008 John Wiley & Sons, Ltd.     

A thermo‐mechanical model for variably saturated soils based on hypoplasticity

The paper presents a mechanical model for non‐isothermal behaviour of unsaturated soils. The model is based on an incrementally non‐linear hypoplastic model for saturated clays and can therefore tackle the non‐linear behaviour of overconsolidated soils. A hypoplastic model for non‐isothermal behaviour of saturated soils was developed and combined with the existing hypoplastic model for unsaturated soils based on the effective stress principle. Features of the soil behaviour that are included into the model, and those that are not, are clearly distinguished. The number of model parameters is kept to a minimum, and they all have a clear physical interpretation, to facilitate the model usefulness for practical applications. The step‐by‐step procedure used for the parameter calibration is described. The model is finally evaluated using a comprehensive set of experimental data for the thermo‐mechanical behaviour of an unsaturated compacted silt. Copyright © 2011 John Wiley & Sons, Ltd.