Optimising the accuracy of a low-cost photogrammetric motion study system

Generally, a low-cost image-based motion study system consists of a set of two or more video imaging cameras and a set of object space control targets. The control targets are required to provide for the computation of exterior parameters of the video frames of objects in motion. Subsequently, the computed exterior orientation parameters are used to compute the position of the motion targets. In general, the accuracy of the motion data is dependent largely on the accuracy of the 3D coordinates of the control targets, the computed camera and lens parameters and the frame rate of the camera. Obviously, it is difficult to improve the frame rate of a low-cost camera; however, the other factors may be optimised analytically. Optimising the accuracy of the control targets is a straightforward process and is discussed briefly in the paper. Optimising the computed camera and lens parameters was the main focus of the research. Consequently, the paper provides the detail of the developed optimising technique. The results show that an optimal principal distance and other lens parameters can be determined by analysing the error of a set of highly accurate object distances. The evaluation shows that the accuracy of the video motion study system can be improved by as much as six times or a reduction of scaling error from 1·06 to 1·01.     

A comparative study of buried structure in soil subjected to blast load using 2D and 3D numerical simulations

The response of underground structures subjected to subsurface blast is an important topic in protective engineering. Due to various constraints, pertinent experimental data are extremely scarce. Adequately detailed numerical simulation thus becomes a desirable alternative. However, the physical processes involved in the explosion and blast wave propagation are very complex, hence a realistic and detailed reproduction of the phenomena would require sophisticated numerical models for the loading and material responses. In this paper, a fully coupled numerical model is used to simulate the response of a buried concrete structure under subsurface blast, with emphasis on the comparative performance of 2D and 3D modeling schemes. The explosive charge, soil medium and the RC structure are all incorporated in a single model system. The SPH (smooth particle hydrodynamics) technique is employed to model the explosive charge and the close-in zones where large deformation takes place, while the normal FEM is used to model the remaining soil region and the buried structure. Results show that the 2D model can provide reasonably accurate results concerning the crater size, blast loading on the structure, and the critical response in the front wall. The response in the remaining part of the structure shows noticeable differences between the 2D and 3D models. Based on the simulation results, the characteristics of the in-structure shock environment are also discussed in terms of the shock response spectra.     

中国大陆科学钻探CCSD-1井0～2000米测井曲线井深自动校正

中国大陆科学钻探(CCSD)主孔CCSD 1井第一阶段0~2 000m钻进完成后,前后2次测井的深度值差异较大,必须对事故后测井的深度值进行校正,以保证数据的正确性。首先对该测井数据进行了一系列的预处理,然后使用多种方法对比分析进行深度校正。在大多数井段取得了良好的效果,达到了事先要求的精度。校正结果表明,相关分析是一种行之有效的方法,但曲线形态差异较大的井段处理还有待研究。全部过程采用计算机自动完成,提高了数据处理工作的效率。     

机载微波辐射计测云中液态含水量

文中介绍了 2 0 0 1～ 2 0 0 2年 4～ 7月吉林省人工增雨期间 ,在中国首次进行的机载对空微波辐射计外场飞行观测试验。观测结果表明 ,仪器可以灵敏地探测出层状云中垂直路径积分云液态水和过冷水含量及其变化 ,揭示了在层状云中嵌入的对流区中有丰富的垂直积分过冷水含量 ,量级可达 10 3 g/m2 。与地面雷达PPI回波强度呈正相关。本文还根据飞机上升 (或下降 )过程的探测数据 ,给出了水平均匀的层状云液态含水量的垂直廓线的实例 ,并进一步讨论了这种方法的应用前景。     

Two-stage prograde and retrograde Variscan metamorphism of glaucophane-eclogites, blueschists and greenschists from Ile de Groix (Brittany, France)

On Ile de Groix, Variscan metamorphic former tholeiitic and alkaline basalts occur as glaucophane-eclogites, blueschists and greenschists in isolated lenses and layers within metapelites. Whole-rock '¹⁸O_SMOW values of the metabasites show limited variations (10.4-12.0‰) and no systematic differences among rock types and metamorphic grades. This provides no argument for large-scale blueschist-to-greenschist transformation driven by infiltration of externally derived fluids. Metamorphic mineralogical changes should have been triggered by internal fluids. Element variations in interlayered blue- and greenschists can be attributed to magmatic fractionation. Assemblages with garnet, clinopyroxene and glaucophane of a high-pressure/low-temperature (HP-LT) metamorphism M1, and NaCa-amphiboles (barroisite, magnesiohornblende, actinolite) of a medium-pressure/medium-temperature metamorphism M2 crystallized during deformation D1. Detailed core-rim zonation profiles display increasing and then decreasing Al^IV in glaucophane of M1. NaCa-amphiboles of M2, mantling glaucophane and crystallized in porphyroblasts, show first increasing, then decreasing, Al^IV and Al^VI. Empirically calibrated thermobarometers allowed P-T path reconstructions. In glaucophane-eclogites of a metamorphic zone I, a prograde evolution to M1 peak conditions at 400-500°C/10-12 kbar was followed by a retrograde P-T path within the glaucophane stability field. The subsequent M2 evolution was again prograde up to >600°C at 8 kbar and then retrograde. Similarly, in metamorphic zones II and III, prograde and retrograde paths of M1 and M2 at lower maximal temperatures and pressures exist. The almost complete metamorphic cycle during M2 signalizes that the HP-LT rocks escaped from an early erosion by a moderate second burial event and explains the long-lasting slow uplift with low average cooling rates.     

加拿大阿尔伯达省西部上泥盆统凯恩组白云岩的成因

加拿大阿尔伯达省西部上泥盆统凯恩组主要由粉晶白云岩和细晶白云岩组成，另外还常见一种充填溶蚀孔洞的亮晶白云石。粉晶白云岩纹理、泥裂和鸟眼等构造发育，其δ＾１３Ｃ为＋１．０‰－＋３．０‰，δ＾１８Ｏ为－６．０‰－－４．３‰，为潮坪上混合水白云化形成。细晶白云岩分布于假整合面之下，其δ＾１３Ｃ为＋０．２‰－＋２．９‰，δ＾１８Ｏ为－６．９‰－－４．６‰，也是混合水白云化的产物。亮晶白云石洁净明亮、晶粒粗     

Prediction of the spatial distribution of the modified mercalli intensity using neural networks

This paper presents the development of an adaptive, non-parametric forecast model for the direct prediction of the spatial distribution of the Modified Mercalli Intensity (MMI) corresponding to an earthquake scenario. The model is based on recent advances in neural networks computation, and is constructed through supervised learning using historical earthquake and regional geological data as training sets. A MMI forecast model for moderate earthquakes with magnitudes between 6 and 7 was developed based on data from the Loma Prieta, Coalinga and Morgan Hill earthquakes. For these data sets, the neural networks forecast model is shown to have excellent data synthesis capability; multiple sets of data can be encapsulated by a relatively simple network architecture. Limited comparison of forecasts made by the neural networks model and conventional models demonstrates that improved accuracy can be achieved. Implementation and operational advantages of the neural networks approach such as general input features, minimum preconceived knowledge of the data sets, the ability to learn and to adapt incrementally and the autonomous and automatic synthesis of the structure underlying the data sets, have been illustrated.     

南极长城站电离层异常的模拟计算和分析

本文采用现有模式，利用长城站电离层观测资料，模拟计算了Ｆ２层峰值高度及子午向热层风昼夜变化等。同时采用了热层风模式计算了长城站热层风的经验预测值。计算结果较好地解释了长城站的两个异常特征。夏季异常即ｆ０Ｆ２最大值出现在夜间。冬季特别是６、７月份临频显著减小。太阳辐射电离与热层中性风的竞相联合作用是导致夏季异常的关键。长城站地理上虽属高纬区，却处在地磁中纬区，这是分析上述异常特征中需要考虑的一个重要因素     

Xenoliths in recent basaltic andesite flows from Arenal Volcano,Costa Rica: inference on the composition of the lower crust

Basaltic andesite flows erupted between 1973 and 1980 from Arenal Volcano contain abundant inclusions of anorthosite, olivine gabbro, and pyroxenites, and megacrysts of olivine and anorthite. The anorthosites with large (20 mm) anorthite grains (An_96-92) exhibit deformation twinning and granulation between grain boundaries. Some olivine gabbros have angular clasts of anorthite with bent twins, pyroxene, and olivine in a finer-grained matrix which is distinctly foliated. These textural features suggest that these inclusions were deformed. An exotic (xenolithic) origin is supported in part by the mineral compositions and the estimated temperatures of equilibration: a temperature of about 975° C is obtained by two-pyroxene and Fe-Ti oxide geothermometers for the gabbros, but two-pyroxene temperatures are higher (1064 to 1120° C) for the basaltic andesite host. The olivine gabbro is thought to have crystallized at a pressure between 8.5 and 9.5 kb; whereas the lava phenocrysts crystallized at a much lower pressure of less than 5 kb. These xenoliths probably represent fragments of the lower crust below Arenal volcano. The lava flows show evidence for some contamination especially from fragments of anorthite broken apart from the larger megacrysts and xenoliths. A few phenocrysts of plagioclase in the lava samples have deformation twins. The unusually high Al₂O₃ content (19.4 to 23.2 wt%) of the lava samples can be attributed directly to the addition of anorthite; in fact the observed chemical variation in the lava flows (the increasing alumina and lime contents with decreasing silica) can be explained by this contamination.     

GPS精密单点定位技术在像控测量中的应用

本文在分析了GPS相对定位及其RTK在像控中应用的优缺点后,提出了精密单点定位进行像控测量的方法。通过实例证明这种方案是完全可行的,并得出了一些对生产实际有益的结论。