共查询到20条相似文献，搜索用时 125 毫秒
1.
Jianjun Zhang Eric W. Gill 《Oceanic Engineering, IEEE Journal of》2006,31(4):779-796
An algorithm is developed for the inversion of bistatic high-frequency (HF) radar sea echo to give the nondirectional wave spectrum. The bistatic HF radar second-order cross section of patch scattering, consisting of a combination of four Fredholm-type integral equations, contains a nonlinear product of ocean wave directional spectrum factors. The energy inside the first-order cross section is used to normalize this integrand. The unknown ocean wave spectrum is represented by a truncated Fourier series. The integral equation is then converted to a matrix equation and a singular value decomposition (SVD) method is invoked to pseudoinvert the kernel matrix. The new algorithm is verified with simulated radar Doppler spectrum for varying water depths, wind velocities, and radar operating frequencies. To make the simulation more realistic, zero-mean Gaussian noise from external sources is also taken into account 相似文献
2.
All ocean wave components contribute to the second-order scattering of a high-frequency (HF) radio wave by the sea surface. It is therefore theoretically possible to estimate the ocean wave spectrum from the radar backscatter. To extract the wave information, it is necessary to solve the nonlinear integral equation that describes the relationship between the backscatter spectrum and the ocean wave directional spectrum. Different inversion techniques have been developed for this problem by different researchers, but there is at present no accepted “best” method. This paper gives an assessment of the current status of two methods for deriving sea-state information from HF radar observations of the sea surface. The methods are applied to simulated data and to an experimental data set with sea-truth being provided by a directional wave buoy 相似文献
3.
Directional wave information from the SeaSonde 总被引：1，自引：0，他引：1
This paper describes methods used for the derivation of wave information from SeaSonde data, and gives examples of their application to measured data. The SeaSonde is a compact high-frequency (HF) radar system operated from the coast or offshore platform to produce current velocity maps and local estimates of the directional wave spectrum. Two methods are described to obtain wave information from the second-order radar spectrum: integral inversion and fitting with a model of the ocean wave spectrum. We describe results from both standard- and long-range systems and include comparisons with simultaneous measurements from an S4 current meter. Due to general properties of the radar spectrum common to all HF radar systems, existing interpretation methods fail when the waveheight exceeds a limiting value defined by the radar frequency. As a result, standard- and long-range SeaSondes provide wave information for different wave height conditions because of their differing radar frequencies. Standard-range SeaSondes are useful for low and moderate waveheights, whereas long-range systems with lower transmit frequencies provide information when the waves are high. We propose a low-cost low-power system, to be used exclusively for local wave measurements, which would be capable of switching transmit frequency when the waveheight exceeds the critical limit, thereby allowing observation of waves throughout the waveheight range. 相似文献
4.
Measurements of the ocean wave directional spectrum using a dual, high-frequency (HF) radar system are presented. A model-fitting technique is used to obtain wave measurements from the radar Doppler spectra. Over 100 h of data, collected NURWEC2 (Netherlands-UK Radar Wavebuoy Experimental Comparison), have been compared with measurements using a WAVEC directional wave buoy. The amplitude and directional characteristics of long-wave components at frequencies of 0.07-0.1 Hz in general show good agreement. Reasonable estimates of the directional spectrum across the whole frequency range are obtained when the assumptions of the model-fitting technique are appropriate. Remaining problems in radar measurement and difficulties in assessing accuracy are discussed 相似文献
5.
In this paper, the radar cross section of flat plates on ocean surfaces is statistically investigated. A combining method of physical optics and geometric optics is applied to establish an effective backscattering analysis procedure. This method is a high-frequency analysis method originally derived from a simplified Stratton-Chu integral equation, assuming that the radar is far away from the target so that Kirchhoff approximation is valid. A Monte-Carlo simulation method is adopted to statistically analyze the effects of undulated ocean surfaces. The ocean surfaces are randomly generated by Pierson-Moskowitz ocean wave spectrum and a directional distribution function. Numerical investigations are carried out for flat plates, with the same height and width but with different inclined angles, on ocean surfaces of various significant wave heights. 相似文献
6.
Measurement of ocean wave spectra using narrow-beam HE radar 总被引：1，自引：0，他引：1
A data interpretation algorithm is developed to extract ocean wave information from HF radar backscatter observed by a narrow-beam antenna system. The basis of this measurement is the inversion of the integral equation representing the second-order radar cross section of the ocean surface. This equation is numerically inverted by approximating it as a matrix equation and pseudoinverting the kernel matrix using a singular value decomposition. As a test of this algorithm, comparisons are made between wave spectrum estimates obtained from a WAVEC buoy and a pair of 25.4-MHz ground wave radars, using data collected during the 1986 Canadian Atlantic Storms Program (CASP). Overall, the results of this experiment have been positive and have demonstrated both the basic feasibility of the inversion algorithm and the wave sensing capability of HF radar. For example, significant wave height estimates deduced by two radars differed from the buoy, in an absolute value sense, by only 0.12 m on average. When using only one radar, the mean difference of this important parameter from the buoy was a reasonable 0.33 m 相似文献
7.
船用X波段雷达被广泛应用于海洋表面波观测和研究。本文给出了一种新的从船用X波段雷达图像中确定主波传播方向的方法。X波段雷达图像中的海浪信号具有明显的尺度性和方向性。同时,curvelet变换作为一种同时具备尺度分辨率和方向分辨率的数学变换,能够对一幅雷达图像在不同尺度、不同方向和不同位置上进行分析。对一幅雷达图像进行curvelet分解并获得curvelet系数后,波浪信号主要集中在某些特定尺度和方向的curvelet系数中,从而我们可以获得带有 方向模糊的波传播方向。进而,通过计算几幅连续采集图像的互相关系数可以消除 方向模糊。同步观测的雷达图像和浮标数据证明了该方法的有效性。 相似文献
8.
Moo-Hyun Kim 《Applied Ocean Research》1992,14(6):353-370
The second-order difference-frequency wave forces on a large three-dimensional body in multi-directional waves are computed by the boundary integral equation method and the so-called FML formulation (assisting radiation potential method). Semi-analytic solutions for a bottom-mounted vertical circular cylinder are also developed to validate the numerical method. Difference-frequency wave loads on a bottom-mounted vertical cylinder and stationary four legs of the ISSC tension-leg platform (TLP) are presented for various combinations of incident wave frequencies and headings. These force quadratic transfer functions (QTF) can directly be used in studying slowly varying wave loads in irregular short-crested seas described by a particular directional spectrum. From our numerical results, it is seen that the slowly varying wave loads are in general very sensitive to the directional spreading function of the sea, and therefore wave directionality needs to be taken into account in relevant ocean engineering applications. It is also pointed out that the uni-directionality of the sea is not necessarily a conservative assumption when the second-order effects are concerned. 相似文献
9.
On the Development of a Second-Order Bistatic Radar Cross Section of the Ocean Surface: A High-Frequency Result for a Finite Scattering Patch 总被引：3，自引：0，他引：3
Eric Gill Weimin Huang John Walsh 《Oceanic Engineering, IEEE Journal of》2006,31(4):740-750
The development of a model for the second-order bistatic high-frequency (HF) radar cross section on an ocean surface patch remote from the transmitter and receiver is addressed. A new approach is taken that allows a direct comparison with existing monostatic cross sections for finite regions of the ocean surface. The derivation starts with a general expression for the bistatically received second-order electric field in which the scattering surface is assumed to be of small height and slope. The source field is taken to be that of a vertically polarized dipole, and it is assumed that the ocean surface can be described, as is usually done, by a Fourier series in which the coefficients are zero-mean Gaussian random variables. Subsequently, a bistatic cross section of the surface, normalized to patch area, is derived. The result is verified by the following two means: 1) the complete form of the bistatic HF radar cross section in backscattering case is shown to contain an earlier monostatic result that has, itself, been used extensively in radio oceanography applications; and 2) the bistatic electromagnetic coupling coefficient is shown to reduce exactly to the monostatic result when backscattering geometry is imposed. The model is also depicted and discussed based on simulated data 相似文献
10.
Second-order features in HF radar Doppler spectral data are compared with a theoretical model of the radar spectrum. The model is the corner reflector double-scatter model which employs a more realistic directional sea spectrum model than those used in earlier works. It includes a frequency-dependent angular spreading function and assumes the existence of spectral energy over a full360deg arising from an apparent second-order wave-wave interaction. Comparison is made with ground wave data collected at the NRL/NOAA/ITS San Clemente Island HF radar. 相似文献
11.
We aim to directly invert wave parameters by using the data of a compact polarimetric synthetic aperture radar(CP SAR) and validate the effectiveness of ocean wave parameter retrieval from the circular transmit/linear receive mode and π/4 compact polarimetric mode. Relevant data from the RADARSAT-2 fully polarimetric SAR on the C-band were used to obtain the compact polarimetric SAR images, and a polarimetric SAR wave retrieval algorithm was used to verify the sea surface wave measurements. Usin... 相似文献
12.
Microwave remote sensing is one of the most useful methods for observing the ocean parameters. The Doppler frequency or interferometric phase of the radar echoes can be used for an ocean surface current speed retrieval,which is widely used in spaceborne and airborne radars. While the effect of the ocean currents and waves is interactional. It is impossible to retrieve the ocean surface current speed from Doppler frequency shift directly. In order to study the relationship between the ocean surface current speed and the Doppler frequency shift, a numerical ocean surface Doppler spectrum model is established and validated with a reference. The input parameters of ocean Doppler spectrum include an ocean wave elevation model, a directional distribution function, and wind speed and direction. The suitable ocean wave elevation spectrum and the directional distribution function are selected by comparing the ocean Doppler spectrum in C band with an empirical geophysical model function(CDOP). What is more, the error sensitivities of ocean surface current speed to the wind speed and direction are analyzed. All these simulations are in Ku band. The simulation results show that the ocean surface current speed error is sensitive to the wind speed and direction errors. With VV polarization, the ocean surface current speed error is about 0.15 m/s when the wind speed error is 2 m/s, and the ocean surface current speed error is smaller than 0.3 m/s when the wind direction error is within 20° in the cross wind direction. 相似文献
13.
Use of nautical radar as a wave monitoring instrument 总被引：2，自引：0，他引：2
Common marine X-Band radars can be used as a sensor to survey ocean wave fields. The wave field images provided by the radars are sampled and analysed by a wave monitoring system (called WaMoS II) developed by the German research institute GKSS. This measuring system can be mounted on a ship, on offshore stations or at coastal locations. The measurement is based on the backscatter of microwaves from the ocean surface, which is visible as ‘sea clutter' on the radar screen. From this observable sea clutter, a numerical analysis is carried out. The unambiguous directional wave spectrum, the surface currents and sea state parameters such as wave periods, wave lengths, and wave directions can be derived. To provide absolute wave heights, the response of the nautical radar must be calibrated. Similar to the wave height estimations for Synthetic Aperture Radars, the so-called ‘Signal to Noise Ratio' leads to the determination of the significant wave height (HS). In this paper, WaMoS II results are compared with directional buoy data to show the capabilities of nautical microwave radars for sea state measurements. 相似文献
14.
15.
基于星载波谱仪海浪方向谱探测原理,仿真了不同海况、风速下的海浪波谱仪接收信号,并采用周期图法、Welch法、AR模型法以及最小方差法共4种不同的调制谱估计方法反演出海浪谱,比较各种调制谱估计方法的海浪方向谱反演性能。仿真结果表明:对于一定方位向下的一维海浪谱反演,不同调制谱估计方法反演海浪谱性能优劣没有绝对的顺序。对于二维海浪谱反演,在成长中海浪条件下周期图法反演性能最差,其他3种方法的反演性能没有绝对优劣顺序;对于成熟风浪,最小方差法在积分能量误差、有效波高误差两个指标上的反演性能最好,在主波波向、主波波长误差上,周期图法反演性能最差,其他3种方法没有绝对优劣顺序。在涌浪条件下,AR模型法反演性能优于其他3种方法。在不同海况下,随着波谱仪中心入射角的下降,反演性能会下降。基于这些仿真结果,本文推荐最小方差法作为充分成长海浪的海浪方向谱反演的调制谱估计方法,AR模型法作为涌浪海浪方向谱反演的调制谱估计方法。 相似文献
16.
Jonathan S. Bathgate Malcolm L. Heron Arnstein Prytz 《Oceanic Engineering, IEEE Journal of》2006,31(4):812-818
A new method for the extraction of swell-wave parameters from high-frequency (HF) radar spectra is presented. The method of extraction of the parameters, period, direction, and height, relies on a frequency-modulation approach that describes the hydrodynamic interaction of the swell waves with the resonant, shorter, Bragg waves. The analysis process minimizes the electromagnetic second-order interaction and a simulation model was used to validate the approach. This simplified method provides a fast means of examining swell conditions over large areas of the ocean surface. Data are acquired using a pair of coastal ocean surface radar (COSRAD) systems deployed at Tweed Heads, Qld., Australia. The radar covers a sweep (approximately 60deg) every 30 min with spatial resolution of the order of 3 km. A sample set of data from this deployment is used in a case study to show the extraction of swell direction and amplitude using these methods. The results support the use of the COSRAD HF radar for mapping swell in the near-shore zone 相似文献
17.
The work describes an inversion algorithm for HF radar measurement of nondirectional wave spectra using an omnidirectional receive/transmit antenna. Such a radar would be suitable for deployment on a stationary ship or drill rig. In this approach, wave information is extracted from the radar observations by numerically inverting the integral equation representing the backscatter return from the ocean. Test results of this technique applied to data collected using a 25.4-MHz radar installed on a ship have been very positive. For the two measurements collected, there is a high degree of correlation between the radar wave estimates and those of a WAVE-TRACK buoy 相似文献
18.
Walsh E. Hancock D. III Hines D. Swift R. Scott J. 《Oceanic Engineering, IEEE Journal of》1985,10(4):376-381
The Surface Contour Radar (SCR) is a 36-GHz computer-controlled airborne radar which generates a false-color-coded elevation map of the sea surface below the aircraft in real time, and can routinely produce ocean directional wave spectra with post-flight data processing which have much higher angular resolution than pitch-and-roll buoys. The SCR range measurements are not error-free and the resulting errors in the elevations corrupt the directional wave spectrum. This paper presents a technique for eliminating that contamination. 相似文献
19.
《Oceanic Engineering, IEEE Journal of》2005,30(3):601-618
Wuhan University's ocean state measuring and analyzing radar (OSMAR2000), working at around 7.5 MHz in the low region of the HF band with a 120-m-long linear receiving antenna array, can measure ocean surface current at ranges of up to 200 km. An ocean surface current algorithm based on direction finding (DF) using the multiple signal classification (MUSIC) method is developed for the OSMAR2000 radar. This paper describes the OSMAR2000 ocean surface current algorithm based on MUSIC and the validation experiments in the East China Sea. The results of the ocean surface current measurements demonstrate that the OSMAR2000 ocean surface current algorithm based on MUSIC is feasible for the long range of ocean surface current mapping with a sufficient bearing resolution. 相似文献
20.
A computer simulation is used to analyze errors in high-frequency (HF) radar ocean surface current measurements. Two pointing algorithms used for current extraction, a direction finding approach using MUltiple SIgnal Characterization (MUSIC) developed by Schmidt (1986), and conventional beam forming, are compared in terms of the effect of variations in sea state parameters on current measurement error. The radar system parameters used in the simulation were taken from the University of Michigan's multi-frequency coastal radar (MCR), which operates on four frequencies from 4.8 to 21.8 MHz and employs an eight-element linear phased array for its receive antenna. Results show MUSIC direction finding to be applicable to phased array systems and to have a better sensitivity to sharp current features, but larger random error than traditional beam forming methods. Also, for cases where beam forming errors are dominated by beam width or low signal to noise ratio, results show MUSIC to be a viable alternative to beam forming 相似文献