Architecture of a distal pre-vegetation braidplain: Cambrian middle member of the Wood Canyon Formation,southern Marble Mountains,California, USA

Architectural element analysis and detailed mapping of a 300 m along-strike exposure of the middle member Wood Canyon Formation, southern Marble Mountains, California, USA, provides new evidence for extensive braided–fluvial channel-belt deposits with adjacent overbank environments. Three-dimensional models constructed using ‘Structure from Motion’ techniques, combined with field-based observations, allowed interpretation of outcrop-scale trends, barforms, channel fills and fine-scale features. The ca 80 m thick member is divisible into five distinct units, including units M1 to M3 that form the bulk of the stratigraphy. Units are defined by stacking patterns of three facies associations (Facies Association 1 to Facies Association 3), each representing the product of a subenvironment within the fluvial system. In Facies Association 1, stacked cosets, interpreted as low-relief fluvial bars and channel fills, preserve vertical-accretion and downstream-accretion elements under unimodal north-north-west palaeoflow, with minor lateral accretion near bar edges. Deposits of Facies Association 2 to Facies Association 3, linked to overbank environments, are found only in unit M2, in the middle 27 m of the middle member. Floodplains, represented by Facies Association 2, include crumbly red-orange intervals of fine to medium-grained sandstone and thinner sets of cross-bedding than Facies Association 1, interbedded with thicker cross-stratification indicative of overbank splay or overland flow aggradation from adjacent channel belts during flood stage. Possible aeolian beds of Facies Association 3 preserve broad festooned trough cross-strata that average 23 cm in thickness; their small size, medium-grained sandstone and iron oxide cement suggest a high water table. The diverse assemblage of interpreted subenvironments, paired with bedform and facies patterns, implies a perennial fluvial system that gradually built large sand bars as the channel belt migrated and avulsed across an unconfined braided–fluvial reach, leaving the overbank area on its flanks subject to weathering and aeolian transport. Despite the occurrence of strata deposited in low-energy and ponded settings, and a marine influence proposed for nearby sections of middle member, no ichnofossils were encountered.     

Trajectory-cell based method for the unmanned surface vehicle motion planning

A trajectory-cell based method was proposed for unmanned surface vehicle (USV) motion planning to combine the expression of the dynamic constraints and the discretization of the search space. The dynamic constraints were expressed by the USV trajectories produced by the mathematical model. The search space was performed by the discretization rules with the consideration of the path continuity, the search convenience and the maneuvering simplification. Therefore, the trajectory-cells were the discretized trajectories, which made the search space meet the USV dynamic constraints, and guaranteed the final spliced path continuous. After abstracting the characteristics of those cells, the available waypoints and headings were represented as the search indexes. Finally, a trajectory-cell based path searching strategy was proposed by determining the cost function of the A* algorithm. The results showed that the proposed algorithm can plan a practical motion path for the USV.     

Experimental investigation on the motion of bubbles in the moonpool with a sonar model inside

Bubbles are becoming a threat to the measurement of equipment and human activities in the moonpool, while little is known about the characteristics of bubbles in the moonpool. We aim to investigate the motion patterns and characteristic of bubbles in the moonpool. To support the investigation, experiments were conducted in a water tunnel. Images of bubbles in and under the moonpool were captured by two high-speed cameras. The software Tema and program PolyParticleTracker were used to track the bubbles in the moonpool. We obtain information of bubbles in the moonpool, including movement patterns of bubbles, generation of bubbles, relationship between amount of bubbles and the freesurface, temporal and spatial distribution of bubbles, the size and the velocities of bubbles.     

中国大陆现今构造变形:三十年的GPS观测与研究

中国大陆的构造变形主要与印度和欧亚两大板块的碰撞有关。印度板块的北向推挤直接导致了世界上最宽旷、最活跃和最复杂的现今构造变形。GPS观测技术问世前,构造变形的定量化研究主要依赖活断层的形貌勘察和区域强震的震源机制解,其结果准确度不足且时空界限模糊。1988年中国地震局在滇西地震实验场首次开展GPS形变监测实验,后又经历国家“攀登项目”、“首都圈GPS地形变监测网”等诸多项目实践,直到“九五”重大科学工程“中国地壳运动观测网络”成功建成,中国大陆现今变形图像才逐步完整和清晰。特别是近年基于“中国构造环境监测网络”2000多站点及近30年累积的其他数据,一个覆盖中国大陆且衔接边邻、框架统一、毫米/亚毫米精度的速度场构建完成。这一基础图像对揭示中国大陆活动构造的运动学和动力学特征、深入研究青藏高原及其周边地区构造形成与演化提供了强有力的观测约束,也为地震危险性的定量化分析奠定了坚实基础。     

The motion of a deep-sea remotely operated vehicle system: Part 1: Motion observations

Rapid and high-resolution motion and tension measurements were made of a caged deep-sea remotely operated vehicle (ROV) system. Simultaneous measurements were made of all six components of motion at the cage and ship A-frame and of the tension in the tether at the ship. Data were collected for cage depths of 0–1765 m. The most significant forcing was in the wave-frequency band (0.1–0.25 Hz) and accounted for over 90% of the variance of vertical acceleration. The vertical acceleration of the cage lagged the acceleration of the A-frame by up to 1.9 s and its variance was larger by up to a factor 2.2. For moderate displacements of the A-frame (≤2 m), the system is only weakly non-linear because the harmonics (3rd and 5th) of the vertical acceleration of the cage account for less than 2% of the total variance. The system is essentially one-dimensional because only the vertical motion of the cage and the vertical motion of the A-frame were coherent, while horizontal motions of the cage were weak and incoherent with any component of motion of the A-frame. The natural frequency of the system is 0.22 Hz at 1730 m, and we estimate that it is within the waveband for depths between 1450 m and the full operating depth of 5000 m.Large vertical excursions of the A-frame produce momentary slack in the tether near the cage. Retensioning results in snap loads with vertical accelerations of 0.5 gravity. Large rates of change of tension and vertical acceleration first occur at the cage during its downward motion and propagate to the surface with the characteristic speed (3870 m s⁻¹) of tensile waves for the tether. Six echoes are clearly detectable at both ends of the tether, and their pattern is extremely repeatable in different snap loads. Due to misalignment of the tether termination with the centres of mass and buoyancy, the cage pitches by up 14° during a snap. The resulting small radius of curvature poses the greatest stress on the tether.     

影响热带气旋结构和运动的两类因子的数值研究

利用一个β平面正压准地转模式，实施了４组时间积分大于５ｄ的试验。结果表明：涡度平流和β效应同样重要，它们对热带气旋的结构和移动均具有明显影响。     

强震动观测的应用

详细阐述了强震动观测的目的、意义和应用范围；分析了强震动观测与通常地震观测的区别；介绍了强震动观测的现状及发展前景。     

On long-period polar motion

 Five separate polar motion series are examined in order to understand what portion of their variations at periods exceeding several years represents true polar motion. The data since the development of space-geodetic techniques (by themselves insufficient for study of long-period motion), and a variety of historical astrometric data sets, allow the following tentative conclusions: retrograde long-period polar motion below about −0.2 cpy (cycles per year) in pre-space-geodetic data (pre-1976) is dominantly noise. For 1976–1992, there is poor agreement between space-geodetic and astrometric series over the range −0.2 to +0.2 cpy, demonstrating that classical astrometry lacked the precision to monitor polar motion in this frequency range. It is concluded that all the pre-1976 astrometric polar motion data are likely to be dominated by noise at periods exceeding about 10 years. The exception to this is possibly a linear trend found in some astrometric and space geodetic series. At frequencies above prograde +0.2 cpy (periods shorter than about 5 years), historical astrometric data may be of sufficient quality for comparisons with geophysical excitation time series. Even in the era of space geodesy, significant differences are found in long-period variations in published polar motion time series. Received: 27 March 2001 / Accepted: 15 October 2001     

Urban flood modelling combining top-view LiDAR data with ground-view SfM observations

Remote Sensing technologies are capable of providing high-resolution spatial data needed to set up advanced flood simulation models. Amongst them, aerial Light Detection and Ranging (LiDAR) surveys or Airborne Laser Scanner (ALS) systems have long been used to provide digital topographic maps. Nowadays, Remote Sensing data are commonly used to create Digital Terrain Models (DTMs) for detailed urban-flood modelling. However, the difficulty of relying on top-view LiDAR data only is that it cannot detect whether passages for floodwaters are hidden underneath vegetated areas or beneath overarching structures such as roads, railroads, and bridges. Such (hidden) small urban features can play an important role in urban flood propagation. In this paper, a complex urban area of Kuala Lumpur, Malaysia was chosen as a study area to simulate the extreme flooding event that occurred in 2003. Three different DTMs were generated and used as input for a two-dimensional (2D) urban flood model. A top-view LiDAR approach was used to create two DTMs: (i) a standard LiDAR-DTM and (ii) a Filtered LiDAR-DTM taking into account specific ground-view features. In addition, a Structure from Motion (SfM) approach was used to detect hidden urban features from a sequence of ground-view images; these ground-view SfM data were then combined with top-view Filtered LiDAR data to create (iii) a novel Multidimensional Fusion of Views-Digital Terrain Model (MFV-DTM). These DTMs were then used as a basis for the 2D urban flood model. The resulting dynamic flood maps are compared with observations at six measurement locations. It was found that when applying only top-view DTMs as input data, the flood simulation results appear to have mismatches in both floodwater depths and flood propagation patterns. In contrast, when employing the top-ground-view fusion approach (MFV-DTM), the results not only show a good agreement in floodwater depth, but also simulate more correctly the floodwater dynamics around small urban feature. Overall, the new multi-view approach of combining top-view LiDAR data with ground-view SfM observations shows a good potential for creating an accurate digital terrain map which can be then used as an input for a numerical urban flood model.     

地球自转极移近120天准周期变化的小波分析及其大气激发机制

本文利用小波变换这一新的频谱分析方法研究了地球自转极移近１２０天准周期变化的时频特征，证实了在极移序列中存在显著的近１２０天准周期振荡，得到了极移准周期变化的周期与振幅随时间变化的规律．以地球自转动力学为基础，在时域内分析了大气变化对自转极移季节内变化的激发．表明大气激发在本文所研究的频段内是极移短周期变化的主要激发源。并发现在极移近１２０天准周期振荡平静时期，发生ＥＬＮｉｎｏ事件，同时日长变化近１２０天准周期变化增强．