MODELING EVOLUTION OF INTERNAL WAVES IN SOUTH CHINA SEA

Internal waves are an important factor in the design of drill operations and production in deep water, because the waves have very large amplitude and may induce large horizontal velocity. How the internal waves occur and propagate over benthal terrain is of great concern for ocean engineers. In the present paper, we have formulated a mathematical model of internal wave propagation in a two-layer deep water, which involves the effects of friction, dissipation and shoaling, and is capable of manifesting the variation of the amplitude and the velocity pattern. After calibration by field data measured at the Continental Slope in the Northern South China Sea, we have applied the model to the South China Sea, investigating the westward propagation of internal waves from the Luzon Strait, where internal waves originate due to the interaction of benthal ridge and tides. We find that the internal wave induced velocity profile is obviously characterized by the opposite flow below and above the pycnocline, which results in a strong shear, threatening safety of ocean structures, such as mooring system of oil platform, risers, etc. When internal waves propagate westwards, the amplitude attenuates due to the effects of friction and dissipation. The preliminary results show that the amplitude is likely to become half of its initial value at Luzon Strait when the internal waves propagate about 400 kilometers westwards.

A hierarchical approach coupled with coarse DEM information for improving the efficiency and accuracy of forest mapping over very rugged terrains

Forest mapping over mountainous terrains is difficult because of high relief Although digital elevation models (DEMs) are often useful to improve mapping accuracy, high quality DEMs are seldom available over large areas, especially in developing countries

Primary succession of algal community structure in desert soil

The microbiotic crust study is among new focuses in investigating on the desertification control. Based on determination of algal crusts with different successive ages (4-, 8-, 17-, 34-, 42-year-old) and unconsolidated sand in the desert area, species composition and clustering analyses were carried out in this study. Results on successional orientation revealed that (1) the abundance of Cyanophyta, specially of Scytonema javanicum gradually decreased; (2) the abundance of Chlorophyta, Bacillariophyta and a species of Cyanophyta, Phormidium tenue increased; (3) the biodiversity increased gradually with the community succession; and (4) biomass of microalgae increased at the early stage, but decreased at the later stage due to the abundance of lichens and mosses. But, the speed of natural succession was so slow that the community-building species was still the first dominant species after 42 years, except that its dominant degree decreased just slightly. However, successive speed and trend were affected by water, vegetation coverage, terrain, time and soil physico-chemical properties as well, especially Mn content in the soil appeared to have a threshold effect.

超大规模地形场景的高性能漫游

超大规模地形场景包含大量的几何和纹理数据，无法一次性载入内存，并具有极高的复杂度，因而无法进行实时绘制．提出一种高性能的外存地形场蒂实时漫游技术．该方法使用离散层次细节技术并结合视点相关的动态连续层次细节选择和过渡．算法为地表的简化提出一种新的基于受限法向锥的误差计算方法，使得模型简化具有轮廓保持和光照保持特性．当生成网格包含三角形数目相当时，该方法比传统的基于几何误差的简化更加符合漫游时视觉的感知规律．场景简化过程中提取出的潜在轮廓特征可以通过巧妙地构建漫游时视线方向上的增量地平线来随时更新场蒂不同部分的可见性信息，并以此控制无用数据页面的载入和无效场景部分的绘制，提高绘制速度．漫游系统采用多线程技术．使CPU、GPU、I／O三者的效率得到充分发挥．并可实时生成具有光照和阴影效果的漫游图像．

动态地形可视化研究

动态地形是指在视景仿真过程中由于环境变化或仿真模型之间的交互而产生的高程和影像数据变化，它是战场仿真的重要研究对象，对战场仿真的逼真度和可信度有着重要影响，直接决定战场模型和地形之间的相互作用方式，如炮弹爆炸产生弹坑，弹坑影响车辆通行。因此，动态地形研究具有重要意义。 本文在开源地形渲染库libMini基础上对动态地形算法进行了研究。libMini库依据视点距离、视角和地形起伏程度对地形进行渲染，具有很好的细节层次模型连续性和较快的渲染速度，支持多分辨率分块地形，在国际上应用广泛，在此基础上进行算法改进和增强可以达到较好的实际应用效果。 首先介绍了libMini的地形渲染算法，并针对该算法计算地形粗糙度的自上而下方法的弱点，提出了自下而上的动态地形高程局部更新算法，将高程计算和渲染速度大约提高了三个数量级，大大改善了动态地形可视化的实时性。由于libMini缺乏动态地形影像更新功能，因此在OpenGL及S3TC纹理压缩算法的分析基础上设计了一种影像更新算法。然后结合高程和影像更新这两个算法实现了一种完整的能够适应多分辨率分块地形的动态地形可视化算法。 最后以虚拟地形工程为例给出了算法的实际应用过程以及相应的弹坑和堑壕模型的动态渲染结果，验证了算法的有效性、实时性和可用性。

一种三维航迹快速搜索方法

本文提出了基于SAS的自动三维航迹规划方法。该方法通过把约束条件结合到搜索算法中去，有效地减小了搜索空间，缩短了搜索时间，从而使三维规划能够用于实时航迹规划。在搜索过程中地形信息得到了充分利用，使算法生成的航迹能够自动回避地形和威胁。实验证明，该方法能够快速有效地完成规划任务，获得满意的三维航迹。

基于libMini的动态地形实时渲染算法

为了减少地形动态变化时的地形计算时间,满足动态地形实时可视化的需要,在地形渲染库libMini的基础上,依据地形动态变化的局部性特点,以及库中LOD(Level ofDetail)算法的具体实现方式,运用局部更新的思想,提出了一种动态地形实时计算和渲染算法.算法避免了在地形动态变化时进行大量重复计算,使得在地形动态变化时所需的计算量大大减少,达到实时渲染要求.实验表明,算法使得局部地形动态变化时地形计算和渲染的时间从秒级降低到毫秒级,可以满足实时渲染要求.

环境因素影响草地柠条生长的主成分及典型相关分析

Principal Component and Canonical Correlation Analysis of the Environmental Factors Influencing the Growth of Caragana korshinskii Kom. in Grassland

高塬沟壑区董志塬沟头溯源侵蚀典型调查研究

详细调查了董志塬地区的西峰区、宁县以及庆城县的沟头溯源侵蚀情况,并对近年来发生前进的沟头进行了详细的实地测量和地形地貌特点分析,对董志塬沟头溯源侵蚀整体情况做出概括。在此基础上将溯源侵蚀的发生类型划分:水力冲刷型、陷穴诱发型、裂缝诱发型和人为诱发型。针对每种类型进行了典型的实例分析。