Application of wavelet transform analysis to landslide generated waves

The aim of this paper is to illustrate the results of a preliminary study on aerial landslide-generated waves, which has been mainly intended to establish a method for analyzing water surface records. Some simple physical experiments, reproducing the Scott Russell's wave generator, were carried out in a small two-dimensional wave flume; the Wavelet Transform (WT) is applied to analyze wave measurements and it is shown that useful information can be obtained by means of this technique. The celerity of impulsively generated waves, reflection by an overflow structure and seiching phenomena of the flume are studied. A discussion of the results along with some remarks about ongoing research is also given.     

Wave grouping characteristics in nearshore Great Lakes

The recently advanced approach of wavelet transform is applied to the analysis of wave data measured in the nearshore areas of the Great Lakes. The conventional spectrum analysis of wave time series in the frequency domain can be readily generalized to the frequency and time domain using the wavelet transform. The traditional Fourier transform approach has not been able to directly assess the time localized nature of wave groups. With the application of wavelet transformation, the relatively unexplored wave grouping characteristics come to light as the predominant feature of wave processes.     

Separation of regular waves by a transfer function method

This paper presents a transfer function method (TFM) which can separate a regular wave field into incident and reflected waves based on the linear wave theory. The TFM uses specific transfer functions and corresponding convolution integrals to separate time series data measured in a combined partial standing wave system into incident and reflected waves. After this separation, estimation of the reflection coefficient becomes very easy. All manipulations have been performed in time domain. Furthermore, this method does not involve the calculation of wave heights and/or phase differences. The present method is demonstrated through numerical sample and physical model experiments carried out in a wave flume. Compared with other methods, the TFM gives much better estimates of the incident wave heights for physical model experiments in this study.     

Analysis and simulation of wave records through fast Hartley transform

The Hartley transform, a real-valued alternative to the complex Fourier transform, is presented as an efficient tool for the analysis and synthesis of ocean surface wave records. Basic theoretical properties of this real-valued transform are briefly reviewed. Similarities and differences between Fourier and Hartley integral transforms, as well as computational benefits and disadvantages between numerical algorithms used to evaluate their discrete versions, are presented. The fast Hartley transform algorithm is used to simulate stationary Gaussian time series of the sea surface elevation and to estimate the spectral density function, the Hilbert transform and the envelope function of wave records.     

Wavelet analysis for processing of ocean surface wave records

Wavelet analysis is a relatively new technique and in the recent years enormous interest in application of wavelets has been observed. This modern technique is particularly suitable for non-stationary processes as in contrast to the Fourier transform, (FT), the wavelet transform (WT) allows exceptional localization, both in time and frequency domains. The wavelet transform has been successfully implemented in signal and image processing, ordinary and partial differential equation theory, numerical analysis, communication theory and other fields. On the other hand, the application of the WT to ocean engineering and oceanography is rare. In this paper the WTs capability to give a full time–frequency representation of the wave signals is demonstrated. The processing of the time series of the non-stationary deep water waves, waves breaking at the tropical coral reefs and mechanically generated waves in the wave flume demonstrates the ability of the wavelet transform technique to detect a complex variability of these signals in the time–frequency domain. Various spectral representations resulting from the wavelet transform are discussed and their application for wave signals is shown.     

Is the wind wave frequency spectrum outdated

This paper presents a detailed examination of the practice of using the frequency spectrum to characterize wind waves. In particular, the issue of stationarity and Gaussian random process in connection with wind wave studies is addressed. We describe a test for nonstationarity based on the wavelet spectrum. When this test is applied to wind wave time series, the results significantly diverge from those expected for a Gaussian random process, thus casting critical doubts on the conventional concept of the wind wave frequency spectrum.     

Wave parameters and functions in wavelet analysis

A preliminary study of wave parameters and functions in wavelet analysis is conducted in this paper. The Morlet wavelet transform is used to calculate the time–frequency wavelet energy density function, its volume (i.e. the total energy), its frequency-integral (i.e. the wavelet smoothed instantaneous wave energy history), its time-integral (i.e. the wavelet spectral density function), and two non-dimensional wave indices (NIF, NIT). The processing of the measured wave data obtained from the Chi-Gu coastal observation tower during the period August 2000 to July 2001 indicates that the inter-comparison of wavelet smoothed instantaneous wave energy history and smoothed instantaneous wave energy history (SIWEH) as defined by Funke and Mansard (Proc 17th Int Conf on Ocean Eng, 1980) can reveal the noise structure of the wave signal. The wave data with index NIF greater than 2 is always accompanied with noise, therefore NIF can be used as one of the data quality criteria. The index NIT is linearly correlated with the significant wave period and with the significant wave height, therefore NIT can be used to study the wave growth and decaying phenomena.     

闽江口硅藻-盐度转换函数建立

目前国内利用定量分析的方法研究河口区古环境屈指可数,闽江口尚缺乏相关研究,本研究旨在闽江口建立硅藻-盐度转换函数,为今后研究闽江口古环境提供科学依据。在对闽江口表层沉积硅藻进行CCA分析后,结果表明盐度对硅藻属种变化具有最大解释量,并在研究区划分出4个区,Ⅰ区硅藻分布受河口外沿岸水体影响;Ⅱ区硅藻分布受潮汐上溯海水入侵影响;Ⅲ区硅藻分布受到潮汐与径流共同影响;Ⅳ区硅藻分布主要受径流影响。通过剔除异常站位及模型比选等手段确定最优硅藻-盐度转换函数为WA-PLS模型下Component 5模型,转换函数关系式为S拟=0. 25+1. 007S实,并以2. 76的平均误差作为补偿提升转换函数精度。     

浅谈数学变换在海洋技术中的应用

根据以往的工作积累,作者在文中介绍了在海洋技术中得到应用的几种数学变换,包括基于Fourier变换的频谱分析、波浪分离、相关分析及定义的H artley实现,连续M orlet小波变换在波浪信号分析中的应用,以及离散正交小波变换的降噪作用与悬沙图像的特征提取。文中通过公式推导和数据比较,展示了数学变换在海洋技术应用中的科学魅力。     

基于传输函数的中尺度涡旋时空连续可视化

本文结合二维流线可视化技术和中尺度涡旋识别技术,提出了3种中尺度涡旋时空连续可视化的方法：基于OW参数的涡旋可视化方法、基于栅格模板的涡旋可视化方法和基于矢量模板的涡旋可视化方法,这3种方法分别基于Okubo-Weiss算法、Faghmous的算法和Liu的算法来进行涡旋识别,同时将流场可视化的结果填充到涡旋内部,以获得更好的可视化效果。在可视化过程中本文引入了传输函数来对涡旋中的流线颜色和透明度进行实时交互,能够在控制界面上通过设置Key值点的颜色和位置来控制速度、涡度和OW参数等信息的显示效果。本文在性能和显示效果方面比较了3种方法的优劣。从性能上来讲,性能由高到低依次为：基于OW参数的涡旋可视化方法、基于栅格模板的涡旋可视化方法和基于矢量模板的涡旋可视化方法。从显示效果上来讲,基于OW参数的涡旋可视化方法在三者中最差,效果中有较多的杂乱的短线,同时涡旋边界较小,局限于涡旋核心区;基于栅格模板的涡旋可视化方法较第一种方法的显示效果有所提升,杂乱的短线较少,涡旋相对完整,但由于数据分辨率不够高的原因,在放大多倍后涡旋边界呈现锯齿状;基于矢量模板的涡旋可视化方法显示效果最好,涡旋完整、饱满。同时,因为首先进行了涡旋边界的重构,将涡旋边界矢量化,涡旋边界更加平滑。相对于传统长时间序列的涡旋可视化的方法而言,这3种方法提供了一个美观、动态和更富信息性的可视化方法,同时由于传输函数的加入,其可以成为科研人员研究涡旋的一个实用的工具。     

Argo观测剖面数据量的时间变化与周期分析

海洋渔业预报使用的遥感数据一般只能获得海洋表面的环境信息,而Argo数据可以为渔业预报提供较深处的温盐数据,为了在渔业预报中按其时间周期进行使用,需要计算它的周期以提高预报质量。通过功率谱估计计算出2001-2008年的数据存在的较长的周期为62．7天和117．5天,较短的周期为4．9天和9．8天,同时还有一个约为7天的不明显周期,观测剖面数据总量在年际与年内都存在较大变化。     

Anisotropy of wind and wave regimes in the Baltic proper

The directional distribution of moderate and strong winds in the Baltic Sea region is shown to be strongly anisotropic. The dominating wind direction is south-west and a secondary peak corresponds to north winds. North-west storms are relatively infrequent and north-east storms are extremely rare. Angular distribution of extreme wind speed also has a two-peaked shape with maxima corresponding to south-west and north winds, and a deep minimum for easterly winds. The primary properties of the anisotropy such as prevailing winds, frequency of their occurrence, directional distribution of mean and maximum wind speeds coincide on both sides of the Baltic proper. The specific wind regime penetrates neither into the mainland nor into the Gulf of Finland or the Gulf of Riga.Properties of the saturated wave field in the neighbourhood of proposed sites of the Saaremaa (Ösel) deep harbour are analysed on the basis of the wave model WAM forced by steady winds. The directional distribution of wave heights in typical and extreme storms is highly anisotropic. Remarkable wave height anomalies may occur in the neighbourhood of the harbour sites.     

Characteristics of developing waves as a function of atmospheric conditions,water properties,fetch and duration

For any specific wind speed, waves grow in period, height and length as a function of the wind duration and fetch until maximum values are reached, at which point the waves are considered to be fully developed. Although equations and nomograms exist to predict the parameters of developing waves for shorter fetch or duration conditions at different wind speeds, these either do not incorporate important variables such as the air and water temperature, or do not consider the combined effect of fetch and duration. Here, the wind conditions required for a fully developed sea are calculated from maximum wave heights as determined from the wind speed, together with a published growth law based on the friction velocity. This allows the parameters of developing waves to be estimated for any combination of wind velocity, fetch and duration, while also taking account of atmospheric conditions and water properties.     

Wavelet transform based coherence analysis of freak wave and its impact

The present paper presents the results of a wavelet transform-based coherence analysis of freak wave and its impact. Wavelet transform has been used as a tool in analyzing signals in the time domain as well as in the frequency domain. The analysis was applied to laboratory-generated freak waves. The wavelet transform of the time history of the freak wave and its impact force revealed that a wide range of frequency components were contained in them. The coherence analysis was conducted on the wave and its impact force time histories. The coherence analysis revealed that some high-frequency components were highly correlated with the impact forces. The present study demonstrates that the wavelet transform can be an alternative tool in the analysis of strongly nonlinear freak wave and its impact.     

基于传输函数的二/三维全时空连续海洋中尺度涡旋流场实时可视化

海洋中尺度涡旋可视化可以将海洋中尺度涡旋的运动规律以图形图像等直观的方式加以展现,是研究海洋中尺度涡旋强有力的工具。然而,现有的可视化方法存在一些不足,如时空连续可视化框架中的流线不能表现全时空连续的运动过程,应用到海洋涡旋提取的特征值受阈值影响严重,交互式传输函数依赖用户经验等。为解决已有的不足,本文首次提出了全时空连续框架和传输函数标准形态模式,将基于区域的涡旋提取技术(?准则)应用到海洋中尺度涡旋可视化中,并提出了全时空连续可视化框架二维及三维的GPU实现方案。实验结果表明,本文的可视化方案达到了实时可交互的级别,对于海洋中尺度涡旋交互式可视化具有重要意义。     

航空重力数据谐波小波滤波中卷积运算的处理

数据的滤波提取是航空重力测量数据处理的一个重要环节。谐波小波滤波器在频域具有良好的盒形谱特征,可以较好地实现信号的滤波。但谐波小波滤波器是一个连续函数,航空重力测量采集的信号是离散的,无法直接进行卷积运算。讨论了谐波小波用于航空重力数据滤波处理时的卷积运算处理方法,给出了谐波小波频域卷积的算法实现过程和仿真算例。     

Analysis of characteristics of time-frequency correlations between runoff, tidal range and salinity in the Changjiang Estuary

Power spectrum and cross-wavelet transform analysis was adopted to study the time-frequency characteristics and multiscale correlations between runoff, tidal range and salinity in the Changjiang Estuary based on the runoff data collected at the Datong Station, the tidal range measured at the Baozhen Station, and the salinity at the Baogang Station from 2008 to 2009. The variations of the salinity showed significant periodicity at scales of 2-3, 7-8, 14-15 and 26-30 d. The correlation between the salinity and the runoff and the tidal range were found to be significantly related to shock at scales of 5-7, 14-15, 26-30 d and 0.5 a. The correlation between the runoff and the salinity was mainly in the same phase, while the correlation between the tidal range and the salinity was in the antiphase. Different frequency bands were related to different degrees, and their relevance increased as the resonance frequency decreased. In addition, changes of the seasonal runoff were obvious. Specifically, a point of discontinuity was reached in early June with a cycle of 7-8 d, which coincided with the periodicity of plum rains in the Changjiang-Huaihe region. High-frequency changes (8-16 d period) of the salinity corresponded to the time domain in January-April 2008, February-April 2009 and October-December 2009 and exhibited an approximately 0.5 a (184 d) long frequency oscillation. Short-period changes were found to be stronger than long-period changes. Cross-wavelet transforms for the salinity, the runoff and the tidal range revealed local features in the time domain, while the significant levels of different periodic oscillations were observed in the frequency domain. The correlation characteristics of the salinity and the runoff were significant in the 80-90 d frequency domain, indicating that the major impact of the runoff on the salinity was reflected in seasonal changes. The tidal range on the small scale of 14-15 and 30-32 d was more obvious than the runoff.     

The near-field tsunami amplitudes caused by submarine landslides and slumps spreading in two orthogonal directions

The aim of this study is to present the solutions for the near-field tsunami amplitudes caused by submarine landslumps and slides spreading in two orthogonal directions. A linearized shallow water wave theory is derived. The transform techniques (Fourier and Laplace transform) are used for the solution of Laplace equation. The results show that if the ratio of the velocties is v₁/v₂=0.1, the numerical results are almost the same as the values obtained for one dimensional movement of the slumps and slides. But, when the ratio of the velocties is v₁/v₂=1, obtained normalized peak amplitudes, η_max/ζ₀ are smaller than the numerical values for one dimensional solution. It is concluded that normalized peak amplitudes for the models are small because of the interaction of the velocities. Numerical examples are presented for various parameters.     

Development of a foraminifera-based transfer function in the Basque marshes, N. Spain: Implications for sea-level studies in the Bay of Biscay

In order to reconstruct former sea level we have developed a foraminifera-based transfer function using three models based on a modern dataset of 59 samples and 23 species obtained from four Basque marshes in Northern Spain. The relationship between observed and foraminifera-predicted elevation illustrated the strong performance of the transfer function (r²_jack ranges from 0.74 to 0.81). These results indicated that precise reconstructions of former sea levels are possible (error ranges from 0.11 to 0.19 m). The transfer function was used to calibrate the foraminiferal assemblages collected from a 50 cm salt marsh core. We placed the foraminifera-based reconstructions into a temporal framework using ¹³⁷Cs, Pb concentrations, and ²¹⁰Pb-derived sediment accumulation rates. The resulting relative sea-level curve is in good agreement with regional tide-gauge data. Both instrumental data and microfossil records suggest a rate of relative sea-level rise of approximately 2 mm yr^− 1 for the 20th century.     

A novel decomposition of the quadratic transfer function (QTF) for the time-domain simulation of non-linear wave forces on floating bodies

In the present study, a novel method is proposed for the separation of the second-order sum- and difference-frequency wave forces—that is, quadratic transfer functions (QTFs)—on a floating body into three components due to wave–wave, wave–motion, and motion–motion action. By applying the new QTF components, the second-order wave forces on a floating body can be strictly computed in the time domain. In this work, the boundary value problems (BVPs) corresponding to the three kinds of QTF components were derived, and non-homogeneous boundary conditions on the free surface and the body surface were obtained. The second-order diffraction potentials were determined using the boundary integral equation method. In the solution procedure, the highly oscillatory and slowly converging integral on the free surface was evaluated in an accurate and effective manner. Furthermore, the application of the QTF components in the time domain was demonstrated. The second-order exciting forces in the time domain were divided into three parts. Each part of these forces was computed via a two-term Volterra series model based on the incident waves, the first-order motion response, and the QTF components. This method was applied to several numerical examples. The results demonstrated that this decomposition yields satisfactory results.