Estimation Of Wave Parameters Research Articles

Estimation of wave parameters based on nearshore wind–wave correlations

A statistical wave model for a specific region was developed to generate long-term wave data in case of the absence of any measured data or to fill the data gaps which occur in a measurement data. Wind data, wave measurement data and a third generation numerical wave model (MIKE21 SW) were used to develop a wave model that is applicable for the research area. The aim of to use such a model is to gain a practical and quick estimation of the wave parameters by using a meteorological station’s wind parameters without having need for a sophisticated wave model which demands more complicated input parameters. In addition, previously developed wave prediction models which are less complicated should not be appropriate for every coastal zone for various reasons. Therefore, the best way to estimate the wave climate for a region is to obtain a site-specific wave model. The Karaburun coastal zone located at the southwest coast of the Black Sea was chosen as the study field. Wind, wave and water level measurements were performed to determine the field data. Wave measurements were carried out at the site by an ultrasonic and pressure type wave gauge between the dates of August 2003 and March 2005. Wave measurement data was used both for the development and calibration of the statistical wave model. The results obtained from the statistical wave model have an RMSE value of 0.29m for the significant wave heights which is very reasonable when the model is considered to be simple and demanding less input data (wind speed, wind direction and fetch length).

Turbulence Measurements in Shallow Water from a Subsurface Moored Moving Platform

Preliminary results are presented from a moored, autonomous instrument measuring the upper ocean turbulent dissipa- tion rate together with the surface gravity wave field. Observations are made in the area approximately 30km southwest of Bergen, Norway between 28 and 30 November 2012, at about 8 m from the surface in 20 m deep water. The platform is the top element of a bottom-anchored mooring line, and moves in response to currents and waves. Shear probes mounted on the nose of the platform allow measurements of dissipation rate of turbulent kinetic energy, ɛ, in the frequency range between 1 to 20Hz in which shear probes are less contaminated by the surface gravity wave disturbances and platform motions. A high-resolution pressure sensor and an acoustic Doppler velocimeter allow estimates of surface bulk wave parameters and measurements of mean currents at a single depth. For the present deployment, in the shallow water within the wave-affected surface layer, at a depth of about 4 significant wave heights, good quality measurements of ɛ were limited by the instrument angle of attack and wave effects. Observations agree well with the scaling of dissipation due to wave breaking. Our preliminary results confirm that successful moored shear probes measurements are possible in the wave-affected layer of the upper ocean.

Detection of Ocean Wave Parameters Using Synthetic Aperture Radar (SAR) Data

This study describes the estimation of spherical wave parameters that appears in Synthetic Aperture Radar (SAR) images acquired over the coast of Chukk, Micronesia. The main causes for the interaction of SAR signals with ocean waves can be retrieved through the Bragg scattering mechanism. Dominant wavelengths were retrieved by means of Fast Fourier Transform (FFT) analysis in terms of peak frequency responses. Sea surface slopes were then obtained from the dispersion relation with consideration of different water wave conditions for each subset area, and wave heights were estimated with the use of dominant wavelengths and sea surface slopes. The work presented in this paper may be useful to retrieve the various wave parameters over different regions. The method used is a novel technique to correlate the relationship between SAR image parameters and dispersion relation.

漁船の操業データを用いた浅海域波浪推算の基礎的検討

漁船の操業データを用いた浅海域波浪推算の基礎的検討

Semiempirical Dissipation Source Functions for Ocean Waves. Part I: Definition, Calibration, and Validation

Abstract New parameterizations for the spectral dissipation of wind-generated waves are proposed. The rates of dissipation have no predetermined spectral shapes and are functions of the wave spectrum and wind speed and direction, in a way consistent with observations of wave breaking and swell dissipation properties. Namely, the swell dissipation is nonlinear and proportional to the swell steepness, and dissipation due to wave breaking is nonzero only when a nondimensional spectrum exceeds the threshold at which waves are observed to start breaking. An additional source of short-wave dissipation is introduced to represent the dissipation of short waves due to longer breaking waves. A reduction of the wind-wave generation of short waves is meant to account for the momentum flux absorbed by longer waves. These parameterizations are combined and calibrated with the discrete interaction approximation for the nonlinear interactions. Parameters are adjusted to reproduce observed shapes of directional wave spectra, and the variability of spectral moments with wind speed and wave height. The wave energy balance is verified in a wide range of conditions and scales, from the global ocean to coastal settings. Wave height, peak and mean periods, and spectral data are validated using in situ and remote sensing data. Some systematic defects are still present, but, overall, the parameterizations probably yield the most accurate estimates of wave parameters to date. Perspectives for further improvement are also given.

A Note on Optimality of Analytical Leakage Compensation at Boundary Frequencies

The interpolated fast Fourier transform (IFFT) was one of the first methods for the highly accurate estimation of sine wave parameters, and its first successful descendant was analytical leakage compensation [which is commonly called analytical solution (AS)]. The AS estimate of frequency is a whole class of solutions whose variance depends on a free parameter K. Thus, to extract the minimum variance solution from a theoretically infinite set, we have to find the optimal value K opt. This paper clarifies the mathematical background of AS and proposes two new solutions for K opt, which reduce the variance of AS estimates of low and high frequencies close to an integer. All inferences are justified by simulations, which confirm the validity of theoretical considerations.

Waves Initiative within SEACOOS

Amongst other ocean state parameters, the development of a wave measurement program was supported as part of the Southeast U.S. Atlantic Coastal Ocean Observing System (SEACOOS). The program focused on supporting nearshore wave measurements using both cabled and autonomous systems but also examined the feasibility of using HF Radar systems for remote estimation of wave parameters. The nearshore stations have provided a significant database on directional wave climate for a number of nearshore locations in the region that provide valuable information to coastal engineers and managers for sustainable development along the coast of the southeastern United States. The ability of Wellen high-frequency radar (WERA HF) to provide wave information was evaluated through a field experiment in SE Florida. The results were encouraging and placed some initial bounds on the confidence to be associated with empirically derived wave height information. Coordination efforts for the development of a comprehensive waves program for the Southeast U.S. were initiated and contributed to the development of the National Wave Observations plan. They also led to the development of a new Regional Coastal Ocean Observing System (RCOOS) that includes developing systems in support of local weather forecast offices in their surfzone and rip-current forecasts.

A noise model for estimated synthetic aperture radar look cross spectra acquired over the ocean

It is well known that look cross spectra processed from synthetic aperture radar (SAR) contain valuable information on ocean waves. With the launch of the European satellite ENVISAT, SAR look cross spectra (SLCS) have become available on an operational basis. Activities therefore exist at different European weather centres to use the data for assimilation into numerical wave models. Furthermore there is scientific interest in SLCS, e.g., concerning the estimation of the phase speed of ocean waves. For the estimation of ocean wave parameters, it is important to have information about the accuracy of SLCS. In this paper, errors of estimated SLCS due to SAR image speckle, spectral estimation errors, and image pattern decorrelation associated with ocean wave motion are analyzed. A probability model is proposed for the estimated SLCS based on the respective cross-spectrum coherence. The model is used to calculate signal-to-noise ratios and confidence limits for the SLCS phase and magnitude, as well as the real and imaginary part. The coherence is factored into a component describing look decorrelation due to SAR image speckle and a second factor describing the effect of sea surface motion. It is shown that the ocean-wave-dependent decorrelation can be simulated using existing nonlinear integral transforms for the look variance spectrum and the SLCS. The decorrelation effect associated with speckle noise is related to SAR system parameters, e.g., the spatial SAR resolution. The probability model is used to investigate the optimal choice of look processing parameters like the look separation time. A statistical analysis based on a global dataset of a reprocessed dataset of European Remote Sensing 2 satellite SLCS is presented confirming the applicability of the probability model. The implications of the results for the retrieval of two-dimensional wave spectra from SLCS are summarized. Possible future applications of the model like, for example, the investigation of the turbulent air flow over waves, are discussed.

Short-Wave Directional Distribution for First-Order Bragg Echoes of the HF Ocean Radars

Abstract Directional distributions of 0.505-Hz ocean waves were investigated using 24.5-MHz HF ocean radars. Recent observations of surface waves reported that the wave directional distribution was bimodal rather than unimodal in fetch-limited conditions. Therefore, the feasibility of using HF ocean radars to identify the bimodal distribution was investigated based on a Monte Carlo simulation. The accuracy of wave parameter estimation and the selection of the model function to describe the wave directional distribution were examined. The number of beam directions is critical to the estimation of wave parameters in the case of the bimodal distribution. It was found that the wave parameter estimation was good if the secondary directional distribution peak amplitude was small. The accuracy of estimation was poor if the secondary distribution peak amplitude was close to the primary distribution peak amplitude. It is necessary to check the error of estimated parameters by simulating first-order Bragg ratios fr...

Unsaturated hydraulic conductivity of structured soils from a kinematic wave approach

Measuring soil hydraulic conductivity in the immediate vicinity of soil water saturation remains challenging, particularly for structured agricultural soils. As a consequence, it is not possible to accurately predict infiltration and drainage rates near saturation with the Darcy-Richards model. Since these rates are accurately predicted by the kinematic wave approach near saturation in structured soils, we assume that the flux-water content relationship could be used to assess hydraulic conductivity within this range of soils and moisture content. Two types of experiments were performed on a structured loamy clay soil in the laboratory: (i) infiltration experiments on samples at laboratory capacity, in order to apply the kinematic wave theory, and (ii) evaporation experiments on saturated samples, in order to assess hydraulic conductivity using Wind's method. Estimating the relationship between the flux of drained water and macropore moisture content according to the kinematic wave theory requires the knowledge of two parameters: a macropore-flux distribution index a and a conductance term b. These parameters were fitted using both a current and a new method. Currently parameters are estimated from the falling limb of the drainage hydrograph whereas the new method uses from the evolution of the drained water flux versus macropore saturation after the end of rainfall. Results have shown that the new method is more reliable than the current one. The estimation of kinematic wave parameters is not influenced by rainfall intensity but depends on initial water content and temporal evolution of the soil sample. Hydraulic conductivity data assessed by both the kinematic wave theory and Darcy's theory seem consistent at values close to “laboratory capacity”, defined in this work as volumetric water content after one-day draining. Thus, the kinematic wave approach could be a reliable tool to assess the hydraulic conductivity of macroporeus soils near saturation.

Contribution of Dense Array Analysis to the Identification and Quantification of Basin-Edge-Induced Waves, Part I: Methodology

Recent earthquakes have shown that edge-generated surface waves can significantly contribute to increased damages. Most observations of edge-generated surface waves are concerning long-period surface waves propagating in large-size valleys. Since travel times of such waves between valley edges can reach several tens of seconds, they are quite easy to isolate. In small-size structures, reverberating wave trains are mixed and very dense array analysis is required for the identification of basin-induced surface wave trains. The city of Grenoble (French Alps) is located in a small-size deep alluvial valley and faces important site effects (Lebrun et al. , 2001). In order to identify and quantify multidimensional site effects in this basin, a very dense array of 29 three-component seismometers over a 1-km aperture was installed within the city. The wave-field complexity as well as the in situ noise characteristics (colored/correlated noise and low signal-to-noise ratio) led us to develop a procedure based on time-frequency coherence of signal waveforms and the multiple signal classification (MUSIC) (Schmidt, 1981) algorithm to identify the main energetic contributions crossing the array. Next, the nature and energy of waves were estimated using some properties of the analytical three-component covariance matrix. Careful methodological investigations were performed in order to better understand and quantify the effects of site constraints on the estimation of wave parameters with the MUSIC technique. Simulations outline the ability of array antennas first to handle difficult scenarios involving multiple, nonstationnary, and correlated propagating phases and second to estimate the polarization and energy of waves. The velocity estimation is shown to be much more unstable than backazimuth estimation, and a low signal-to-noise ratio introduces some variation in estimates. Finally, considering the very large number of identified waves, a statistical view of final estimates is suggested for improving the reliability of analysis. In an accompanying article (Cornou et al. , 2003), we use this method to investigate the entire wave field of seismic events recorded by the array in order to isolate basin-induced waves. Manuscript received 21 June 2002.

New methods to improve convergence of sine fitting algorithms

One of the recommended test methods in Analog to Digital testing standards is based on least square sine fitting algorithms. The parameter estimation provided by these algorithms is exposed to errors due to different causes. In particular convergence to local minimums of the error function is an open problem. In this paper we present new methods that improve results in sine wave parameter estimation when the frequency is unknown, assuring convergence even in the presence of saturation, noise or distortion. These new methods are also usable in other signal processing applications since they work without loss of quality when only one period of the input signal is acquired.

Estimation of seismic-wave parameters and signal detection using maximum-likelihood methods

A broad-band maximum likelihood method is presented for the detection of and parameter extraction from seismic events using wideband data recorded by an array of seismic stations. The statistical characteristics of finite Fourier-transformed data motivate the use of approximate maximum-likelihood (ML) methods which allow simultaneous detection and wave-parameter estimation. The detection strategy based on the likelihood ratio indicates the presence of a seismic event and resolves different phases of seismic events arriving within a time interval of interest. The corresponding slowness vectors of the phases are simultaneously estimated by optimization of the likelihood function over parameters of interest. The potential of the wideband ML method is demonstrated on GERESS data and compared to conventional f– k analysis showing advantages of the former in detection and resolution.

Evaluation of Marine Wave Radar (Part II)

The importance of the knowledge of ocean waves parameters for the naval and ocean engineering field is not questionable, and the limitations of the available methods to obtain this valuable information is the leading motivation to the search of better approaches and improved analysis methods. The use of conventional marine radar PPI images allows the estimation of wave parameters on a real-time basis, using both space and time information about the evolution of the ocean surface waves. In Part I, the two-dimensional (spatial information) spectral analysis of one radar PPI image was performed, and the limitations of this approach could be evaluated using radar images numerically generated. To overcome those limitations the wave number-frequency spectrum is calculated from a set of radar images through a three dimensional FFT. The understanding of the components of this spectrum and the comparison with the expected dispersion shell allows the filtering of noise and correction of aliased frequencies. In this paper, simulated radar images generated as described in Part I and experimental data are used to evaluate the analysis method. The significant wave height was recovered using a new approach based on the shadow ratio present on the radar image.

Hybrid optical processing of sea surface imagery for the estimation of wave parameters

With the availability of high spatial resolution space-borne sensors, the wave parameters like wave propagation direction, wavelength of the dominant wave etc., are estimated from the Fourier spectra of ocean scene imageries. The hybrid optical processor is the most suitable for the analysis of imageries, since it utilises the parallel processing capability of the optical processor for generating the Fourier spectra. An attempt has been made to use a hybrid processor with wedge-ring sampling detector array for the estimation of wave parameters and the results are encouraging.

A statistical study of the structure, saturation and sources of inertio-gravity waves in the lower stratosphere observed with the MU radar

Using wind data monitored by the MU radar at Shigaraki, Japan (35°N, 136°E) in the three years of 1986–1988, a statistical analysis is made of inertio-gravity waves (IGWs) with short vertical wavelengths (⩽ 4 km) and long ground-based periods (⩾ 10 h) which are dominant in the lower stratosphere in all seasons. The intensity of the IGWs is at its peak in winter when a strong subtropical westerly wind jet is situated over Japan. The zonal component of vertical momentum flux associated with the IGWs in winter is mostly negative and the magnitude decreases with altitude, suggesting a strong interaction between IGWs and the background wind field. The parameters of the wave structure are estimated by a hodograph analysis, taking into consideration the effect of vertical shear of the background wind that is not negligible in winter. The obtained parameters, such as the vertical and horizontal energy propagation directions, vertical and horizontal wavelengths, and intrinsic period, are compared between two periods with a strong subtropical jet including winter and with a weak jet including summer. The degree of saturation of IGWs, defined as the ratio of amplitude of the horizontal perturbation velocity parallel to the horizontal wavenumber vector to the intrinsic horizontal phase velocity, is also statistically and directly examined using the results of wave parameter estimation. It is shown that the degree of saturation is larger in winter than in summer and that there are few oversaturated IGWs even in winter. Moreover, in order to examine the generation mechanisms of the IGWs, an analysis is made from two points of view: geostrophic adjustment of the westerly wind jet and the topographic effect. The meridional propagation direction of IGWs is examined in a section of latitude and altitude relative to the jet axis using ECMWF operational data. Most of the IGWs observed in the 12–18 km height region (above the ground) in winter propagate meridionally toward the jet axis, indicating that geostrophic adjustment at least just as the jet axis is not the main generation mechanism of the IGWs. On the other hand, the characteristics of intensive IGWs propagating westward relative to the background wind in the 18–22 km height region in winter are in good accord with mountain waves excited in strong westerly winds near the surface.

The effect of the earth's rotation on internal waves in the wake of a moving pressure area

Plane waves generated in a continuously stratified ocean by a steadily moving surface pressure area are studied in a linear statement with the earth's rotation taken into account. General properties of the wave process are examined. Qualitative estimates of internal wave parameters in the internal wave wake are derived for model density stratification with an isolated density gradient.

An Assessment of Wave Observations from Ships in Southern Oceans

Observations of wind waves and swell from ship reports are investigated. Comparisons are made between estimates of wave parameters made from ships in southern oceans by calculating correlations as a function of ship separation, and analyzing the resulting series. It is shown that there is very little consistency in the reporting of wind wave and swell periods and swell directions. Heights fare considerably better, although it is shown that one observer still fails to account for at least 50% of the variance in the observations of another observer. Further, some comparisons of ship-reported wave heights with measurements show a high bias in the observations of at least 0.5 meters. Some weak quality control criteria fail to be met by a large number of observations. Despite the inconsistencies, the intercomparisons show that the data is representative of many of the physical characteristics of wavefields, and therefore can be useful in climatological studies.

ESTIMATION AND OPTIMIZATION OF KINEMATIC WAVE PARAMETERS1

ABSTRACT: This study presents analytic and graphical techniques for estimation and optimization of kinematic wave parameters. Because the techniques are derived from the kinematic wave theory, the optimized parameter values will have minimum bias in them.