基于地理信息可视化的线状符号表达方法的研究     

郑春燕  胡华科 《现代测绘》2004,27(1):44-46

本文根据线状要素地理信息表达的需要，对线状符号进行了分类．在分析了线状符号的视觉变量之后，给出了其图案单元的数据结构。最后结合线状符号的分解、组合特性提出了线状符号的配置方法。  相似文献   

区域气候模拟研究中的物理集合技术   总被引：4，自引：0，他引：4  

钟科  王汉杰 《气象学报》2004,62(6):776-781

文中介绍了基于MM 5有限区域模式的物理集合构造方法 ,通过对模式中的 5种物理过程加以扰动、组合而得到一个有 19个成员的物理集合系统 ,并用其对 1998年夏季发生在中国东部地区的异常洪涝天气气候特征进行了模拟研究。以集合预报的 3种基本释用方法 ,对集合模拟产生的大量输出结果作了细致的分析 ,发现在区域气候模拟中 ,引入物理集合是可行的 ;它为区域气候数值研究提供了更多的手段和信息 ;集合系统存在的不足之处在于 :集合成员间离散程度不足、集合模拟范围较狭窄 ,这使得离差对误差的实际预报能力低于潜在预报能力 ,也使集合概率预报的精度降低。  相似文献   

南海夏季风爆发的EOF分析          下载免费PDF全文

朱敏  张铭 《气象科学》2004,24(3):261-268

本文利用1983～1992年的NCEP资料．对南海夏季风爆发做经验正交函数分解，分析了主要模态的时空变换特征。结果表明：太阳辐射北移，是南海夏季风爆发的最重要的因素。南海夏季风爆发前后，在典型季风区850hPa上东西风有一次重大调整。南半球中高纬西风带槽脊振幅的增强和北半球副热带系统经向环流的加大是南海夏季风爆发的重要原因。西太平洋副高的迅速减弱东撤，导致南海夏季风的爆发。  相似文献   

时间滞后与奇异向量初值生成方法的比较试验   总被引：11，自引：2，他引：11       下载免费PDF全文

杨学胜  冷亭波等 《应用气象学报》2002,13(1):62-66

简单介绍了国家气象中心基于奇异向量初值生成方法的神威集合预报准业务系统, 它主要包括资料的前处理、客观分析、预报模式、初值扰动的生成、后处理、产品制作和系统监控七个部分, 共有 32 个成员。 提出了 12 个成员的时间滞后法集合预报系统的实施方案, 并与奇异向量法进行了对比试验。 结果表明, 不论是距平相关系数还是均方根误差, 奇异向量法在绝大多数区域和预报时效都比时间滞后法好。  相似文献   

On the Role of Wind Direction in ERS SAR Signatures of Internal Waves on the Iberian Shelf     

I. B. Araú  jo  J.C.B. da Silva  S. A. Ermakov  I. S. Robinson 《Journal of Atmospheric & Ocean Science》2002,8(4):269-281

The relationship between internal wave (IW) signatures in Synthetic Aperture Radar (SAR) images and wind velocity is investigated. The effect of the wind velocity relative to the IW propagation direction on the IW signature is studied by means of a defined signature mode parameter ( S m ). S m is the parameter that quantifies the signature of the IW intensity profile in relation to the mean backscatter of the image background.

A wind contrast model based on a simple first-order Bragg scattering theory is combined with hydrodynamic modulation theory to explain the modulation of IW signatures. It takes into account the modulation of short-scale surface waves by the effect of the relative variations of wind velocity and the surface currents generated by the IWs.

It is shown that the signature mode parameter increases with the angle between the wind velocity and the IW propagation direction so that IWs propagating against the wind direction are imaged mostly as positive sign signatures, while those propagating in the wind direction are mostly negative sign signatures.  相似文献   

噪声条件下的干涉SAR相位解缠   总被引：5，自引：0，他引：5  

岳焕印  郭华东  韩春明  李新武  王长林 《测绘学报》2002,31(2):151-156

为了获得更为精确的相位解缠结果，利用经验模态分解算法对干涉相位图进行了噪声抑制，随后用Flynn最小不连续算法对滤波结果进行了相位解缠。对比中值滤波和C．Bo自适应滤波算法，以及预处理共轭梯度相位解缠算法的结果证明，经验模态分解滤波不驻能有效地抑制噪声，而且可以保持相位的细节信息和相位条纹的边缘信息，同时表明，在噪声条件下，Flynn相位解缠算法可以获得更为精确的真实相位。  相似文献   

A Direct Inverse Model to Determine Permeability Fields from Pressure and Flow Rate Measurements     

Geert K. Brouwer  Peter A. Fokker  Frank Wilschut  Wouter Zijl 《Mathematical Geosciences》2008,40(8):907-920

The determination of the permeability field from pressure and flow rate measurements in wells is a key problem in reservoir engineering. This paper presents a Double Constraint method for inverse modeling that is an example of direct inverse modeling. The method is used with a standard block-centered finite difference method. With an a priori grid block permeability field as input, two forward runs are made: the first is constrained with the measured pressures; the second is constrained with the measured flow rates. We calculate the pressures in the grid block centers from the first run, while from the second run we calculate the fluxes through the faces between the grid blocks. Substitution of these pressures and fluxes into Darcy’s law then yields the transmissibilities at the faces and hence the permeabilities in the grid blocks. In this way the “hard” data (measured pressures and flow rates) are always honored while the “soft”, geological data can be incorporated at the discretion of the geologist. Using a synthetic example, we demonstrate the method and compare the results with another method: Ensemble Kalman Filtering. The two methods agree within the scope of their applicability. The Double Constraint method focuses initially on determining spatial distributions of the permeability field for single-phase, steady state flow. For history matching an extension is required to non-steady state, two-phase flow conditions, which is already possible with EnKF. We are currently investigating the possibility of combining the two methods, whereby the strengths of the two methods could be fully exploited.  相似文献   

基于经验模态分解的GPS基线解算模型   总被引：1，自引：1，他引：0  

王坚  高井祥  王金岭 《测绘学报》2008,37(1):0-113

非建模系统误差是影响高精度GPS基线解算精度的一个重要因素,文章给出基于经验模态分解的GPS基线解算模型,有效消弱系统误差对基线解的影响。在现有经验模态分解理论的基础上,定义经验模态分解的多尺度分解与重构结构,并由此给出基于经验模态的系统趋势分离模型,依据累积标准化模量的均值随尺度的变化确定系统误差与噪声分离尺度的选择标准。给出基于经验模态分解的GPS基线解算的技术路线,首先计算GPS相位双差观测方程的浮点解残差序列,分离出系统误差并用于修正GPS双差观测值,重新计算双差浮点解,采用Lambda算法固定整周模糊度,计算固定基线解,从而消弱系统误差对基线解算的影响,提高基线固定解的可靠性。并采用实测GPS数据验证模型,F-ratio指数与W-ratio指数表明系统误差消弱后,基线固定解可靠性得到明显提高,重新计算的残差序列表明系统误差得到很好的消弱。  相似文献   

3rd Ishihara Lecture: An investigation into why liquefaction charts work: A necessary step toward integrating the states of art and practice     

《Soil Dynamics and Earthquake Engineering》2015

This paper is a systematic effort to clarify why field liquefaction charts based on Seed and Idriss׳ Simplified Procedure work so well. This is a necessary step toward integrating the states of the art (SOA) and practice (SOP) for evaluating liquefaction and its effects. The SOA relies mostly on laboratory measurements and correlations with void ratio and relative density of the sand. The SOP is based on field measurements of penetration resistance and shear wave velocity coupled with empirical or semi-empirical correlations. This gap slows down further progress in both SOP and SOA. The paper accomplishes its objective through: a literature review of relevant aspects of the SOA including factors influencing threshold shear strain and pore pressure buildup during cyclic strain-controlled tests; a discussion of factors influencing field penetration resistance and shear wave velocity; and a discussion of the meaning of the curves in the liquefaction charts separating liquefaction from no liquefaction, helped by recent full-scale and centrifuge results. It is concluded that the charts are curves of constant cyclic strain at the lower end (V_s1<160 m/s), with this strain being about 0.03–0.05% for earthquake magnitude, M_w≈7. It is also concluded, in a more speculative way, that the curves at the upper end probably correspond to a variable increasing cyclic strain and K_o, with this upper end controlled by overconsolidated and preshaken sands, and with cyclic strains needed to cause liquefaction being as high as 0.1–0.3%. These conclusions are validated by application to case histories corresponding to M_w≈7, mostly in the San Francisco Bay Area of California during the 1989 Loma Prieta earthquake.  相似文献   

Ambient noise surface wave tomography of the Makran subduction zone,south-east Iran:Implications for crustal and uppermost mantle structures     

Mahsa Abdetedal  Zaher Hossein Shomali  Mohammad Reza Gheitanchi 《地震科学（英文版）》2015,28(4):235-251

Seismic ambient noise of surface wave tomography was applied to estimate Rayleigh wave empirical Green's functions(EGFs) and then to study crust and uppermost mantle structure beneath the Makran region in south-east Iran.12 months of continuous data from January 2009 through January 2010,recorded at broadband seismic stations,were analyzed.Group velocities of the fundamental mode Rayleigh wave dispersion curves were obtained from the empirical Green's functions.Multiplefilter analysis was used to plot group velocity variations at periods from 10 to 50 s.Using group velocity dispersion curves,1-D vs velocity models were calculated between several station pairs.The final results demonstrate significant agreement to known geological and tectonic features.Our tomography maps display low-velocity anomaly with SW-NE trend,comparable with volcanic arc settings of the Makran region which may be attributable to the geometry of Arabian Plate subducting beneath the overriding the Lut block.The northward subducting Arabian Plate is determined by high-velocity anomaly along the Straits of Hormuz.At short periods(20 s),there is a sharp transition boundary between low- and high-velocity transition zone with the NW trending at the western edge of Makran which is attributable to the Minab fault system.  相似文献