The attenuation of tidal and subtidal oscillations in the Patos Lagoon estuary     

E. H. L. Fernandes  I. Mariño-Tapia  K. R. Dyer  O. O. Möller 《Ocean Dynamics》2004,54(3-4):348-359

The single, long and narrow channel that usually connects choked coastal lagoons to the ocean can serve as a natural hydraulic low-pass filter that reduces or eliminates tidal and subtidal effects inside the lagoon. This study proposes an alternative method of estimating the attenuation of the tidal and subtidal oscillations throughout the Patos Lagoon estuary. The attenuation is estimated for conditions of contrasting river runoff and weather (summer and winter). A high-pass/low-pass filter (fast fourier transformation technique – FFT) is applied to time series of sea-surface elevation (SSE) measured at the mouth of the Patos Lagoon. The resulting high-frequency (tidal) and low-frequency (subtidal) signals are used in independent simulations to force the TELEMAC-2D model. Attenuation of the tidal and subtidal signals throughout the estuary is estimated by applying cross-spectral analysis between the model-generated SSE time series at different locations throughout the estuary and the filtered SSE time series measured at the mouth. Results from the proposed method suggest that: (1) the low-frequency (subtidal) oscillations are less attenuated and propagate further than the high-frequency (tidal) oscillations in the Patos Lagoon estuary; (2) the filtering capability of the Patos Lagoon estuary is expected to follow a seasonal pattern, although further investigations on an interannual time scale are recommended in order to confirm this hypothesis; (3) the influence of the oceanic boundary processes on the SSE dynamics of the lagoon is restricted to the lower estuary. Further inland, the local forcing generated by the wind and freshwater input is likely to be the main forcing effect controlling the dynamics of the system. The proposed method proved to be an efficient and alternative way of estimating the attenuation of energy in the tidal and subtidal bands throughout the access channel of a choked coastal lagoon located in an area of reduced tidal influence.Responsible Editor: Iris Grabemann  相似文献   

SAR干涉图的静态小波域MAP法滤波   总被引：6，自引：0，他引：6  

岳焕印  郭华东  王长林  杨虎 《遥感学报》2002,6(6):456-463

SAR干涉图中的斑点噪声是对相位解缠的极大障碍，为了得到更精确的地形模型，必须在相位解缠前对干涉图进行斑点噪声滤波。提出了一种干涉图的小波域多尺度滤波算法。对干涉图的实部和虚部分别进行处理，用Pearson分布系确定了信号和噪声项小波系数的概率密度函数，然后用最大后验概率（Maximum A Posterior,MAP)准则估计无噪数据的小波系数。将本算法和另外3种滤波算法进行比较。结果表明，本滤波算法对SAR干涉图有很强的噪声抑制能力，并能保持干涉图的相位细节信息和相位分布。  相似文献   

Effect of filtering on drift and anisotropy parameters determined by full correlation analysis     

H. Chandra 《Journal of Earth System Science》1989,98(4):327-338

The effect of low-pass filtering on the various drift and anisotropy parameters obtained by full correlation analysis of spaced receiver records is studied theoretically, assuming Gaussian correlation functions. A decrease in the characteristic velocityV _cis shown with increasing filtering, unlessV ≫ V _v, whenV _cincreases with filtering. The ratioV _c/V however shows an increase as the decrease in the true drift velocityV is steeper thanV _c. An increase in the size of the ground pattern with increasing filtering is also shown, while the axial ratio for anisotropic patterns shows a decrease. The results are verified with experimental data recorded earlier at Tiruchirapalli.  相似文献   

一种船载海面通量观测的校正方法   总被引：2，自引：0，他引：2  

钱莉英  周乐义  周晓平 《海洋科学》1994,18(4):59-63

设计了一种用滤波法校正船载超声测风测量仪数据、计算海－气通量交换的方法。对１９８８，１９８９两年西太平洋海域考察期间超声测风测温仪的实测资料作了订正，订正了船体运动、特别是摇摆运动对风速的影响，用涡旋相关法计算了海面边界层的感热能量、动量通量、阻力系数和稳定度值。分析了海面上能量、阻力系数随大气状况的变化规律。计算结果表明，海面上的通量、阻力系数与水平风速和稳定度之间存在着合理的有规律的关系，证明  相似文献   

航空重力测量数据的小波滤波处理   总被引：16，自引：7，他引：9       下载免费PDF全文

柳林涛  许厚泽 《地球物理学报》2004,47(3):490-494

构造三类连续小波函数对航空重力测量数据进行小波滤波处理. 三类连续小波函数分别用于对测量数据在某一空间尺度（或时间尺度）上的低通,一阶求导和二阶求导滤波. 着重介绍三类连续小波函数的构造原理与过程,并说明其相对于传统的数字滤波器的优势. 对系统的技术参数（滤波器窗口宽度参数δ 和尺度参数s）进行了调试实验. 实算结果显示了方法的可行性和有效性.  相似文献   

Retrieval of small-relief marsh morphology from Terrestrial Laser Scanner, optimal spatial filtering, and laser return intensity   总被引：1，自引：0，他引：1  

A. Guarnieri  A. Vettore  F. Pirotti  M. Menenti  M. Marani   《Geomorphology》2009,113(1-2):12

Marshes are ubiquitous landforms in estuaries and lagoons, where important hydrological, morphological and ecological processes take place. These areas attenuate sea action on the coast and act as sediment trapping zones. Due to their ecosystem functions and effects on coastal stabilization, marshes are crucial structures in tidal environments, both biologically and geomorphologically, and are fundamental elements in wetland restoration and coastal realignment schemes. The spatially-distributed study of the geomorphology of intertidal areas using remotely-sensed digital terrain models remains problematic, owing to their small relief, often of the order of a few tens of centimetres, and to the presence of short and dense vegetation, which strongly reduces the number of resolvable ground returns. Here, we use high-resolution Terrestrial Laser Scanning ( 200 returns/m²) to retrieve a high-resolution and high-accuracy Digital Terrain Model within a tidal marsh in the Venice lagoon. To this aim we apply a new filtering scheme to Terrestrial Laser Scanner data which selects the lowest values within moving windows, whose optimal size is determined with the aid of a limited number of ancillary Differential GPS data in order to maximize resolution while ensuring the identification of true ground returns. The accuracy of the filtered data is further refined using classifications of the intensity of the returns to extract additional information on the surface (ground or canopy) originating the returning laser beam. Validations against about 200 reference Differential GPS ground elevation observations indicates that the best separation of canopy and ground signals is obtained using a low-pass filter with window size of the order of 1 m and the maximum likelihood classifier to further refine the detection of ground returns. In this case the average estimation error is about 1 cm (slight overestimation of ground elevation), while its standard deviation is about 3 cm. Our approach allows the separation of laser returns coming from the low marsh vegetation from those coming from the marsh surface. The overall result is a new observation technique producing Digital Terrain and Digital Surface Models in areas with very small relief, which is shown to provide unprecedented high-resolution and high-accuracy characterizations of marsh morphology.  相似文献   

地震系统行业网Ospf路由过滤   总被引：2，自引：0，他引：2  

赵军  王松  张蕾 《地震研究》2009,32(4)

简要介绍了Ospf路由协议工作原理、通过路由跟踪分析和路由过滤的方式,从理论和事例两个方面,解释了路由过滤的基本语法和配置方法。地震在行业网运行中出现的故障处理解决办法。  相似文献   

Techniques for mode separation in Rayleigh wave testing     

Mourad Karray  Guy Lefebvre 《Soil Dynamics and Earthquake Engineering》2009

The spectral analysis of surface wave (SASW) developed in the early eighties has opened the way to the use of surface waves for the definition of shear wave velocity profiles in soil deposits or pavement structures without the need of any borings or intrusion. The SASW testing procedure was designed to minimize the contribution of higher modes and thus assumes that the Rayleigh waves which propagate at the surface belong only to the fundamental mode. Several studies have however demonstrated that, in some conditions, higher Rayleigh modes can contribute significantly to the dispersion curve. Different tests configurations exist today to deal with Rayleigh mode problem by the use of an array of receivers. In spite of that, the SASW configuration remains attractive due to the limited number of receivers, as well as, the Rayleigh modes contributing in SASW records configuration can be identified by multiple-filter technique and isolated using time-variable filters. The proposed techniques are first validated by simulated records and then applied to SASW records obtained in the field. The study confirms that higher modes can participate and even dominate in SASW records. An important contribution of higher Rayleigh modes can also exist, even if the shear wave velocity increases regularly with depth. The higher Rayleigh modes can significantly affect the accuracy of the shear wave velocity profile if they are not properly identified and separated. A multi-mode inversion process is shown to be important to have an accurate soil characterization.  相似文献   

Glacial isostatic adjustment in Fennoscandia from GRACE data and comparison with geodynamical models     

Holger Steffen  Heiner Denker  Jürgen Müller 《Journal of Geodynamics》2008,46(3-5):155

The Earth’s gravity field observed by the Gravity Recovery and Climate Experiment (GRACE) satellite mission shows variations due to the integral effect of mass variations in the atmosphere, hydrosphere and geosphere. Several institutions, such as the GeoForschungsZentrum (GFZ) Potsdam, the University of Texas at Austin, Center for Space Research (CSR) and the Jet Propulsion Laboratory (JPL), Pasadena, provide GRACE monthly solutions, which differ slightly due to the application of different reduction models and centre-specific processing schemes. The GRACE data are used to investigate the mass variations in Fennoscandia, an area which is strongly influenced by glacial isostatic adjustment (GIA). Hence the focus is set on the computation of secular trends. Different filters (e.g. isotropic and non-isotropic filters) are discussed for the removal of high frequency noise to permit the extraction of the GIA signal. The resulting GRACE based mass variations are compared to global hydrology models (WGHM, LaDWorld) in order to (a) separate possible hydrological signals and (b) validate the hydrology models with regard to long period and secular components. In addition, a pattern matching algorithm is applied to localise the uplift centre, and finally the GRACE signal is compared with the results from a geodynamical modelling. The GRACE data clearly show temporal gravity variations in Fennoscandia. The secular variations are in good agreement with former studies and other independent data. The uplift centre is located over the Bothnian Bay, and the whole uplift area comprises the Scandinavian Peninsula and Finland. The secular variations derived from the GFZ, CSR and JPL monthly solutions differ up to 20%, which is not statistically significant, and the largest signal of about 1.2 Gal/year is obtained from the GFZ solution. Besides the GIA signal, two peaks with positive trend values of about 0.8 Gal/year exist in central eastern Europe, which are not GIA-induced, and also not explainable by the hydrology models. This may indicate that the recent global hydrology models have to be revised with respect to long period and secular components. Finally, the GRACE uplift signal is also in quite good agreement with the results from a simple geodynamical modelling.  相似文献   

神经网络自适应数字滤波器技术   总被引：1，自引：1，他引：0  

洪志全 《物探化探计算技术》2000,22(2):137-139

作者在本文中介绍了如何利用 BP神经网络实现自适应滤波器的算法和关键技术 ,这对于在地质勘测、工业控制领域的数据采集中的数据数字滤波处理具有极其重要的指导意义  相似文献