全球六边形离散格网的矢量线数据绘制精度控制     

于文率  童晓冲  贲进  谢金华 《地球信息科学学报》2015,17(7):804-809

全球离散格网系统是一种新型的地球空间数据模型,是平面格网模型在球面上的扩展。由于六边形的几何结构优势,经常被用于球面离散格网的构建。在平面格网向球面映射过程中,因球面的不可展性,格网上的距离和方向都会发生巨大变化,导致矢量数据球面格网化绘制的精度无法得到保证,这成为矢量数据在全球离散格网显示的一个重要瓶颈,直接制约了球面格网上空间度量关系的建立。本文针对全球六边形离散格网上矢量线数据的绘制问题,研究了平面-球面映射过程,对直线方向影响的统计变化规律,对矢量线数据的格网化表达进行了精度控制,使得平面格网上的矢量绘制方法,能在球面格网上进行高精度的绘制,并保证矢量数据的球面格网绘制误差严格控制在当前层次格网的一个单元内,为格网化数据的高精度显示和格网空间度量的建立奠定了理论基础。  相似文献   

Lateral accretion in a deep-marine channel complex: implications for channellized flow processes in turbidity currents     

MASON DYKSTRA  BEN KNELLER† 《Sedimentology》2009,56(5):1411-1432

Some deep-marine channels show striking similarities to fluvial channels, despite major differences in the properties of the flows that they conduct. Some field observations from deep-marine channel deposits within a Late Cretaceous palaeo-canyon in the Rosario Formation of Baja California, Mexico, that bear on these comparisons have been reported. These channel deposits contain erosively based lateral accretion sets. These sets are generally a few metres thick and resemble fluvial point bar deposits. Sediment movement and deposition within these accretion deposits was induced by turbidity currents several to many times thicker than the depth of the channel, moving at several metres per second. The inclined sets define laterally migrating and sinuous channels locally at a high angle to the confining canyon. The instantaneous channel widths varied from 6 to 39 m, the depths from 2·5 to 4 m and the sinuosities from 1·3 to 3·1. Palaeocurrent data, taken mostly from clast imbrication in conglomerates, indicates current modes along the channel thalweg, but with other directions representing either secondary flow (oriented primarily up the point bar) or over-passing canyon-confined flow. It is suggested that, at times, the lower part of the turbidity currents flowing down the channels behaved similarly to within-bank fluvial currents, with a cross-channel component of flow towards the cut bank, and return flow at the bed sweeping up the point bar. At other times, this secondary circulation may be absent or reversed, which may be related to changes in flow thickness, coupling with the overriding flow and possible flow separation.  相似文献   

PNEUMATIC ACOUSTIC ENERGY SOURCE*     

BEN F. GILES 《Geophysical Prospecting》1968,16(1):21-53

In recent years considerable work has been done to devise a satisfactory non-dynamite seismic system that would replace dynamite in offshore areas. Prior to the advent of digital recording and processing, the non-dynamite sources have generally not provided the depth of penetration or the resolution required for satisfactory seismic interpretation. More recent developments in non-dynamite offshore marine sources include adaptation of the Vibroseis from a land unit to a marine unit, and adaptation of the Dinoseis unit from a land to a marine unit. The SUE (Seismic Underwater Explorer) system is a thermodynamic non-dynamite source utilizing a mixture of propane and oxygen detonated in a special chamber approximately 15 feet below the water surface. This source gives penetration to more than 4 sec in areas typified by Gulf of Mexico type geology and shows deeper penetration than had previously been obtained by dynamite along the western United States in areas with 20 lb charge limitations. A pneumatic source, the airgun, has been in production use in the United States since June 1966. This non-dynamite source provides an intriguing amount of versatility and can be expanded to provide additional energy as necessary to obtain the penetration desired. Tests using systems comprised of from eight to twenty-three airguns show penetration in excess of 5 seconds in many areas. Power spectra comparisons both in amplitude and frequency content demonstrate that this is a controlled source generating a controlled seismic wavelet and a controlled frequency spectrum that can be tailored to fit requirements of particular areas. Sample sections obtained in the Gulf of Mexico and the Pacific Ocean offshore California show adequate penetration to 5.0 seconds reflection time. Quantitative measurements with the airguns demonstrate the effect of:

• 1 Variation of the number of guns in the system;
• 2 Shaping the frequency spectrum by using different sizes of airguns in the system;
• 3 Effects on signal-to-noise ratios as a result of stacking several small energy sources together;
• 4 Reproducibility of the initial pulse wavelet from shot to shot.

The improvement in record quality as a result of advanced digital processing with non-dynamite sources is comparable to that obtained with dynamite sources. Non-dynamite sources make additional improvements possible where high source multiplicity is advantageous. Excellent dynamic correlations yield accurate velocity control as well as definitions of apparent velocities attributable to multiples and primary-to-multiple amplitude relationships. Non-dynamite sources are being used more and more extensively in offshore exploration. The advent of digital recording and processing provides a means for improving depth of penetration and resolution of many non-dynamite sources.  相似文献   

基于TIFF和XML标准的瓦片金字塔模型     

贲进 童晓冲张衡  丛凤波 《测绘学院学报》2005,22(3):184-186

随着数字地球、数字城市研究的深入，多分辨率空间数据模型已成为GIS研究的热点之一，瓦片金字塔作为管理栅格型空间数据的有效手段更得到了广泛应用。文中分析了普通金字塔模型的缺点，在此基础上设计并实现了符合TIFF和XML标准的通用数据模型；通过应用证明了模型的实用价值。  相似文献   

Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia   总被引：5，自引：0，他引：5  

S. MORAD  H. N. BEN ISMAIL†  L. F. DE  ROS  I. S. AL-AASM‡  N-E. SERRHINI† 《Sedimentology》1994,41(6):1253-1272

The fluvial Triassic reservoir subarkoses and arkoses (2409·5–2519·45 m) of the El Borma oilfield, southern Tunisia, were subjected to cementation by haematite, anatase, infiltrated clays, kaolinite and K-feldspar at shallow burial depths from meteoric waters. Subsequently, basinal brines controlled the diagenetic evolution of the sandstones and resulted initially in the precipitation of quartz overgrowths, magnesian siderite, minor ferroan magnesite and anhydrite. The enrichment of siderite in ¹²C isotope (δ¹³C_PDB= - 14·5 to - 9‰) results from derivation of carbon from the thermal decarboxylation of organic matter. During further burial, the precipitation of dickite and pervasive transformation of kaolinite into dickite occurred, followed by the formation of microcrystalline K-feldspar and quartz, chlorite and illite, prior to the emplacement of oil. Present day formation waters are Na-Ca-Cl brines evolved by the evaporation of seawater and water/mineral interaction and are in equilibrium with the deep burial (≤ 3·1 km) minerals. These waters are suggested to be derived from the underlying Silurian and Devonian dolomitic mudstones.  相似文献   

基于遗传算法的影像分级决策融合     

童晓冲  张永生  贲进 《遥感学报》2006,10(2):197-203

在传统的影像单级融合技术基础上提出了基于遗传算法的分级影像决策融合方法，该方法适用于影像之间的冗余度、互补程度和融合顺序均未知的情况。算法采用模糊逻辑和遗传算法确定了影像间的冗余度和互补程度，并由此得出了近似的影像最优分级决策融合方式，最后通过实验比较了分级融合、单级融合以及源影像的目视效果和数学统计结果。  相似文献   

球面离散网格在椭球面上的扩展及变形分析     

贲进  童晓冲  张永生  张衡 《测绘科学》2006,31(4):25-27,59

球面离散网格数据模型是管理海量数据的有效途径之一,现有网格建立的基础是球面而不是椭球面,因而不能满足地理空间数据高精度应用的需要。围绕这一问题,建立了球面到椭球面的几种对应关系,从而将球面网格投影到椭球面上;结合实验分析了网格的最大最小边长比、最大最小夹角比和最大最小面积比,从而为该方法的实际应用奠定了基础。  相似文献   

基于球面六边形网格系统的空间信息处理方法     

张永生  贲进  童晓冲  戴晨光 《测绘学院学报》2006,(2)

利用球面离散网格系统管理全球海量空间信息是一种受到普遍关注的新途径。文中提出的方法首先采用施奈德等积多面体投影将平面多分辨率六边形网格映射到球面构成网格系统;然后通过边界点四元组将球面六边形网格之间的空间关系转化为球面三角四叉树处理,利用扩展的QTM编码方案在3轴离散网格坐标系下实现了经纬度和单元地址码之间的转换;最后提出了单元分析和检索算法。实验结果表明,这种数据处理方法直接对单元地址编码进行操作,具有较高的效率。  相似文献   

基于六边形网格的球面Voronoi图生成算法     

贲进  童晓冲  张衡  江刚武 《测绘学院学报》2006,(5)

利用二十面体施奈德等积多面体投影构建了球面多分辨率六边形层次网格;通过边界四元组将六边形单元分解到四元三角形及其子单元中处理;利用改进的四元三角网编码方案建立了网格的数字空间、单元层次编码模型和不同实体在球面上的表达方法。在此基础上,提出了球面Voronoi图的生成算法。实验结果表明该算法与现有算法相比具有更高精度。  相似文献   

Deposition and diagenesis of carbonate conglomerates in the Kremenara anticline, Albania: a paragenetic time marker in the Albanian foreland fold-and-thrust belt   总被引：2，自引：0，他引：2  

LIESBETH BREESCH  RUDY SWENNEN  BEN DEWEVER  AJET MEZINI† 《Sedimentology》2007,54(3):483-496

This paper addresses the diagenesis of carbonate conglomerates in that it assesses the potential of conglomerates in refining the paragenetic history in complex structural areas, such as the Albanian foreland fold‐and‐thrust belt. Of major interest are stylolites (burial and tectonic) which are restricted to conglomerate fragments or which crosscut the conglomerate matrix. Based on the inferred age of stylolite development in relation to burial, uplift and tectonic history, and the Lower to Middle Miocene age of the conglomerates, the succession of diagenetic events was subdivided into several stages. The Poçem polymict transgressive carbonate conglomerate (Kremenara anticline, central Albania) was deposited in a shallow marine environment. These conglomerates are covered by intertidal rhodolithic packstones–grainstones. The stable‐isotope signature of these packstones–grainstones (δ¹⁸O_V‐PDB = −1·0 to +0·7‰; δ¹³C = +1·0 to +1·4‰) plots is within the range of marine Early and Middle Miocene values. Shortly after deposition of the conglomerates, micritization, geopetal infill and acicular calcite cementation took place. A first calcite vein generation is interpreted as having formed from a Messinian brine during shallow burial. Burial stylolites developed during further burial in the Pliocene. These stylolites serve as an important diagenetic time marker. The post‐burial stylolite meteoric calcite vein cement probably precipitated during the following telogenetic stage. Karstification and calcite concretion precipitiation pre‐date overturning of the western limb of the anticline. Reopening of subvertical fractures and tectonic stylolites in the western limb of the Kremenara anticline, followed by oil migration, represents one of the latest diagenetic events. These fractures and stylolites provide major pathways for hydrocarbon production.  相似文献