近地天体望远镜配置大阵面CCD后轴外像差的校正

近地天体望远镜由SI600S (4k×4k) CCD升级为STA1600LN (10k×10k) CCD后,观测视场由4 deg~2增至9 deg~2,可用视场直径由望远镜原设计视场的3.14°增至4.28°,超出原设计36%,同时作为CCD密封窗的场镜增厚8.75 mm;两个因素导致10k CCD成像的轴外像差增大,视场外围的像质变差.依据望远镜原始设计光学参数,借助光学设计软件ZEMAX进行像质改善尝试,最终选择在10k CCD场镜前插入一个由两片球面透镜组成的场改正镜,使10k CCD的轴外像差得到校正.同时还提出了一个进一步拓展近地天体望远镜观测能力的设计方案,将望远镜的可用视场从目前的14.38 deg~2扩展至28.27 deg~2.     

珠江口低盐透镜现象的声传播特性分析

低盐透镜现象是珠江口陆架海域常见的一种中尺度现象,它的出现会影响水下声传播环境。利用南海北部陆架区的CTD资料分析了低盐透镜的结构特征,基于简正波和射线模型,建立二维波导环境,设置不同声源条件,对低盐透镜环境的声传播特性进行了研究。结果表明:低盐透镜会在海水上层形成声道,距离15 km处其传播损失较没有低盐透镜的情况小约15 dB。虽然低盐透镜声道厚度通常较小,但是较大的盐度梯度可以保证声道对声能的有效传播。当频率高于截止频率的声源置于低盐透镜内,声道效应有助于声音的远距离传播。     

Mitigating systematic error in topographic models for geomorphic change detection: accuracy,precision and considerations beyond off-nadir imagery

Unmanned aerial vehicles (UAVs) and structure-from-motion photogrammetry enable detailed quantification of geomorphic change. However, rigorous precision-based change detection can be compromised by survey accuracy problems producing systematic topographic error (e.g. ‘doming’), with error magnitudes greatly exceeding precision estimates. Here, we assess survey sensitivity to systematic error, directly correcting topographic data so that error magnitudes align more closely with precision estimates. By simulating conventional grid-style photogrammetric aerial surveys, we quantify the underlying relationships between survey accuracy, camera model parameters, camera inclination, tie point matching precision and topographic relief, and demonstrate a relative insensitivity to image overlap. We show that a current doming-mitigation strategy of using a gently inclined (<15°) camera can reduce accuracy by promoting a previously unconsidered correlation between decentring camera lens distortion parameters and the radial terms known to be responsible for systematic topographic error. This issue is particularly relevant for the wide-angle cameras often integrated into current-generation, accessible UAV systems, frequently used in geomorphic research. Such systems usually perform on-board image pre-processing, including applying generic lens distortion corrections, that subsequently alter parameter interrelationships in photogrammetric processing (e.g. partially correcting radial distortion, which increases the relative importance of decentring distortion in output images). Surveys from two proglacial forefields (Arolla region, Switzerland) showed that results from lower-relief topography with a 10°-inclined camera developed vertical systematic doming errors > 0·3 m, representing accuracy issues an order of magnitude greater than precision-based error estimates. For higher-relief topography, and for nadir-imaging surveys of the lower-relief topography, systematic error was < 0·09 m. Modelling and subtracting the systematic error directly from the topographic data successfully reduced error magnitudes to values consistent with twice the estimated precision. Thus, topographic correction can provide a more robust approach to uncertainty-based detection of event-scale geomorphic change than designing surveys with small off-nadir camera inclinations and, furthermore, can substantially reduce ground control requirements. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

某上游法尾矿坝抗滑稳定性分析的几点思考

通过某上游法尾矿坝抗滑稳定性分析,对比分析了坝体加高、浸润线条件、排渗系统运行状况和透镜体简化对尾矿坝抗滑稳定性的影响。结果表明,该尾矿坝抗滑稳定性随坝体的加高而降低;排渗系统运行状况对尾矿坝抗滑稳定性的影响超过坝体加高对尾矿坝抗滑稳定性的影响;根据一定简化原则减少透镜体,从而简化剖面形状和计算复杂程度,是一种能反映工程实际但比较保守的分析方法;拟静力法并非适合于所有的尾矿堆积坝抗震稳定性分析,即便采用其所得结果也可能会出现较大偏差。     

The kinematic history of the Singhbhum Shear Zone

The progressive deformation of the Singhbhum Shear Zone (SSZ) involved the initiation of a mylonitic foliation, its deformation by three generations of reclined folds and superposition of two later groups of folds, i.e., a group of asymmetric folds with subhorizontal or gently plunging axes and a group of gentle and open, transverse and more or less upright folds. The occurrence of sheath folds and U-shaped deformed lineations indicate that the reclined folds were produced by rotation of fold hinges through large angles. The total displacement along the SSZ was compounded of displacements along numerous mesoscopic shear zones. The cleavages in the shear lenses and the mesoscopic shear zones cannot be distinguished as C and S surfaces. They have the same kinematic significance and were produced by ductile deformation, although there were localized discontinuous displacements along both sets,-of cleavages. A mylonitic foliation had formed before the development of the earliest recognizable folds. Its time of formation and folding could be synchronous, diachronous or partly overlapping in time in the different domains of the SSZ.     

轻非水相液体在地下环境中的运移特征与模拟预测研究

通过自行设计制备的二维砂箱模拟轻非水相液体(LNAPL)在湿润多孔介质中的渗漏,得出LNAPL在地下环境中的入渗、迁移及分布规律,并利用多相流体理论对其污染机理进行分析.在实验基础上建立模型来预测渗漏的基本特征,即渗流带中污染锋面扩展速度和透镜体的最终形状,预测结果与实测结果较为接近.这种预测模型对控制和治理地下水中LNAPL污染是至关重要的.     

气候变化与生计和贫困研究的认知

本文介绍了IPCC第五次评估报告中关于气候变化、生计和贫困研究的认知。研究者采用生计透镜的方法,评估气候变化与多维角度的贫困之间的相互作用。气候变化作为“威胁放大器”,对于贫困人口及其生计增加了额外的负担。同时强调了气候变化可能产生新的贫困人口类群。通过对气候变化政策响应的综述,得出气候变化政策响应通常并不能使贫困人口受益的结论。     

Determination of the Velocity of Meteors Based on Sinodial Modulation and Frequency Analysis

In meteor photography the velocity of meteors is generally obtained from a chopper which blocks periodically the incident light beam in front of the camera lens. In this paper I examine modulation of the meteor trail instead with a sinodial function and use frequency analysis to compute accurately the mean atmospheric velocity.     

构造透镜体中成矿雏形断裂的形成过程

以应力-应变曲线峰值为界,岩石破坏可分为 2个阶段,前阶段发育为雏形断裂,后阶段发育成宏观断裂。雏形断裂是一种特殊的断裂形式,在自然界中少见宏观断裂。与宏观断裂不同的是,雏形断裂既无断层面,又无碎裂岩,仅由小（微）裂隙组成。裂隙通常互不连通,总体具优选方向,且集中成透镜状裂隙群。裂隙群中部裂隙最发育,往边部渐趋消失。透镜状裂隙群之间呈雁列式排布,易发育和保存于构造透镜体弱应变域中。主要变形机制有液压致裂和应力腐蚀。形成前经历过微裂隙闭合、弹性变形和微裂隙生长扩容 3个阶段。以 2个中型金矿床为实例,研究了这一新发现的成矿构造的地质特征,认为变形分解、液压致裂和构造泵吸三者相互耦合,在雏形断裂形成与成矿过程中发挥关键作用。雏形断裂发育阶段可以形成独立的工业矿体。     

On deposits controlled by tectonic lenses

Tectonic lenses (e.g., boudinage structures,pinch-and-swell structures) are common geologicalstructures observed in various scales ranging fromseveral hundreds of kilometers (e.g., lenticular terranesor massifs) in orogenic belts to a few millimeters (e.g.,core-mantle structures and porphyroclasts) in petro-graphic thin-sections. The most frequently observedtectonic lenses are those developed in metamorphicrocks where compositional layers with distinctrheological strengths coexist. No matter h…