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1.
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
2.
船用X波段导航雷达凹波形成的海杂波图像中包含丰富的海浪、海表层流信息.借鉴合成孔径雷达(SAR)估计有效波高的方法,假设有效波高与雷达回波强度信噪比的平方根成线性关系,可由X波段雷达图像估计得到海浪的有效波高.用此方法主要分析小麦岛海域实验数据,结果显示,直流滤波后计算的信噪比估计的有效波高比不进行直流滤波结果符合得好;而按波浪浮标测得有效波高数据的高低,分两段分别进行线性拟合获取校准系数,估测的有效波高更加准确. 相似文献
3.
The popular methods to estimate wave height with high-frequency(HF) radar depend on the integration over the second-order spectral region and thus may come under from even not strong external interference. To improve the accuracy and increase the valid detection range of the wave height measurement, particularly by the smallaperture radar, it is turned to singular peaks which often exceed the power of other frequency components. The power of three kinds of singular peaks, i.e., those around ±1,±2~(1/2) and ±1(2~(1/2)) times the Bragg frequency, are retrieved from a one-month-long radar data set collected by an ocean state monitoring and analyzing radar,model S(OSMAR-S), and in situ buoy records are used to make some comparisons. The power response to a wave height is found to be described with a new model quite well, by which obvious improvement on the wave height estimation is achieved. With the buoy measurements as reference, a correlation coefficient is increased to 0.90 and a root mean square error(RMSE) is decreased to 0.35 m at the range of 7.5 km compared with the results by the second-order method. The further analysis of the fitting performance across range suggests that the peak has the best fit and maintains a good performance as far as 40 km. The correlation coefficient is 0.78 and the RMSE is 0.62 m at 40 km. These results show the effectiveness of the new empirical method, which opens a new way for the wave height estimation with the HF radar. 相似文献
4.
Several important statistical properties of the HF sea echo and its Doppler power spectrum, which are useful in optimizing the design of radar oceanographic experiments, are established. First- and second-order theories show that the echo signal (e.g., the voltage) should be Gaussian; this is confirmed with experimental surface-wave data i) by comparison of the normalized standard deviation of the power spectrum at a given frequency with its predicted value of unity, and ii) by cumulative distribution plots of measured spectral amplitudes on Rayleigh probability charts. The normalized standard deviation of the dominant absolute peak amplitudes of the power spectrum (which wander slightly in frequency) are shown from experimental data to besim 0.7 for the first-order peaks andsim 0.5 for the second-order peaks. The autocorrelation coefficient of the power spectra is derived from measured data and interpreted in terms of the spectral peak widths; from this information, the correlation time (or time between independent power spectrum samples) iS shown to besim 25-50 s for radar frequencies above 7 MHz. All of these statistical quantities are observed to be independent of sea state, scattering cell size, and relatively independent of radar operating frequency. These quantities are then used to establish the statistical error (and confidence interval) for radar remote sensing of sea state, and it is shown, for example, that 14 power spectral samples result in a sample average whose rms error about the true mean is 1.0 dB. 相似文献
5.
利用X波段雷达提取海浪信息的分析 总被引：2，自引：0，他引：2
利用X波段雷达海浪信息提取系统,通过对龙口屺姆岛海域岸基试验数据分析,获得了有效波高、主波频率、主波波向等海况参数,并和该区域的浮标数据进行了比较分析,结果表明利用X波段雷达系统能够有效地获得海况信息。 相似文献
6.
随机波浪下泰勒离散系数的时域解 总被引：1，自引：0，他引：1
利用Wolk提出的粒子追踪方程,通过等分频率法划分不规则波谱,利用MATLAB做粒子运动模拟计算,得到无因次化泰勒离散系数K/D随时间t变化的曲线;通过与Huang等得到的P-M谱的泰勒离散系数K/D计算结果比较证明了本计算方法的可靠性。采用该方法研究了不规则波条件下,波序列(同一谱型不同波面序列)和谱型(谱峰周期、有效波高、谱峰升高因子)对波浪离散系数的影响;计算结果表明:同一谱型不同波序列对泰勒纵向离散系数稳定值和稳定时间无影响;不规则波谱峰周期越大,纵向离散系数K/D越小,稳定时间越短;有效波高越大,纵向离散系数K/D越大,稳定时间越长;谱峰升高因子越大,泰勒离散系数K/D越大,稳定时间越长;与规则波相比,不规则波的泰勒离散系数K/D的值略小10%~30%。 相似文献
7.
Wave-tank measurements show that some wind waves travel at a speed that corresponds more closely to the spectral peak frequency than to the linear dispersion relation. However, Bragg echoes sampled and averaged in space and time by HF radars tend to obey the linear dispersion relation. Resolution of the dilemma will require new measurements with incisive attention to their meaning. 相似文献
8.
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
9.
便携式高频地波雷达台湾海峡浪高观测 总被引：2，自引：1，他引：1
As an important equipment for sea state remote sensing, high frequency surface wave radar(HFSWR) has received more and more attention. The conventional method for wave height inversion is based on the ratio of the integration of the second-order spectral continuum to that of the first-order region, where the strong external noise and the incorrect delineation of the first- and second-order Doppler spectral regions due to spectral aliasing are two major sources of errors in the wave height. To account for these factors, two more indices are introduced to the wave height estimation, i.e., the ratio of the maximum power of the second-order continuum to that of the Bragg spectral region(RSCB) and the ratio of the power of the second harmonic peak to that of the Bragg peak(RSHB). Both indices also have a strong correlation with the underlying wave height. On the basis of all these indices an empirical model is proposed to estimate the wave height. This method has been used in a three-months long experiment of the ocean state measuring and analyzing radar, type S(OSMAR-S), which is a portable HFSWR with compact cross-loop/monopole receive antennas developed by Wuhan University since 2006. During the experiment in the Taiwan Strait, the significant wave height varied from 0 to 5 m. The significant wave heights estimated by the OSMAR-S correlate well with the data provided by the Oceanweather Inc. for comparison, with a correlation coefficient of 0.74 and a root mean square error(RMSE) of 0.77 m. The proposed method has made an effective improvement to the wave height estimation and thus a further step toward operational use of the OSMAR-S in the wave height extraction. 相似文献
10.
针对利用X波段海浪雷达回波图像反演海浪参数(波高、波向、波周期)的需要,而海浪雷达回波信号的采集和存储是利用雷达回波图像序列反演海浪参数的必要前提,提出了基于PXI-9280 A/D采集卡对X波段海浪雷达回波进行采集的方案.具体介绍了PXI-9280 A/D采集卡的功能特性,海浪雷达回波信号样式,设计并完成了基于VC 6.0的采集和存储软件,并对使用该采集卡需要注意的实际问题给予说明.此外,还搭建了实验平台,给出了基于PXI-9280 A/D采集卡在我国南海某海域中采集数据并回放得到的海浪雷达回波图像,得到较满意的结果. 相似文献
11.
Ship detection with high-resolution HF skywave radar 总被引：2，自引：0，他引：2
This paper presents an overview of ship detection by high-frequency (HF) skywave backscatter over-the-horizon radar (OTHR). Ships have been detected at ranges of 2000 km or more by OTHR that uses sufficient resolution in the radar spatial and Doppler frequency domains. The HF sea-echo Doppler spectrum limits the target signal-to-clutter ratio (SCR), as a function of the ocean wave-height distribution, wind direction, radio frequency, and ship target radial velocity. Maximum sea-clutter spectrum purity, and hence larger SCR, is achieved with the use of stable single-mode ionospheric propagation. Real-time measurement and interpretation of ionospheric propagation features therefore must guide the choice of OTHR operating frequency. Experimental data recorded at the ONR/SR1 Wide Aperture Research Facility (WARF) bistatic OTHR in central California demonstrate reliable ship detection in the Northeast Pacific Ocean. WARF transmits 1-MW average effective radiated power, using a linear frequency-modulated continuous-wave (FMCW) waveform, and receives with a 2.55-km broadside array of vertical monopole element pairs. Swept bandwidths as high as 200 kHz have been used. Sufficient spectral resolution is achieved with a coherent integration time (CIT) of 12.8 s. Longer CIT, and autoregressive (AR) spectral analysis techniques such as Marple's algorithm, have been used to improve Doppler resolution. 相似文献
12.
Ocean surface currents can be estimated, over a large coastal area, by utilizing the backscatter of high frequency (HF) radar waves from ocean gravity waves. Although the overall backscatter mechanism is complicated, the surface current information is contained within the spectral characteristics of two dominant Bragg components. The accuracy of the current estimate, following the usual FFT-based spectral estimate, is limited by the frequency resolution of the FFT and the time-varying characteristics of the Bragg components. This paper describes a high resolution parametric estimation of the ocean currents based on a recently proposed technique for analyzing time-varying signals. This technique, together with a time-domain ocean clutter model, allows all the Bragg signal information to be extracted from the two dominant eigenvalues and eigenvectors of a matrix constructed from the radar data. Using signals from an operational coastal surveillance radar, current estimates made using this technique are compared with those estimated by the conventional FFT-based method 相似文献
13.
Dennis Trizna Lillian Xu 《Oceanic Engineering, IEEE Journal of》2006,31(4):904-918
In this paper, we describe a high-frequency (HF) radar capable of multifrequency operation over the HF band for dual-use application to ship classification and mapping ocean current shear and vector winds. The radar is based on a digital transceiver peripheral component interconnect (PCI) card family that supports antenna arrays of four to 32 elements with a single computer, with larger arrays possible using multiple computers and receiver cards. The radar makes use of broadband loop antennas for receive elements, and a number of different possibilities for transmit antennas, depending on the operating bandwidth desired. An option exists in the choice of monostatic or multistatic operation, the latter providing the ability to use several transmit sites, with all radar echo signal reception and processing conducted at a single master receiver site. As applications for such a multifrequency radar capability, we show measurement and modeling examples of multiple frequency HF radar cross section (RCS) of ships as an approach to ship target classification. Results of using 32 radar frequencies to measure the fine structure in ocean current vertical shear are also shown, providing evidence of one edge of a 1-3-m deep uniform flow masked at the surface by wind-driven current shear in a different direction. Other applications of current-shear measurements, such as vector wind mapping and volumetric current estimation in coastal waters, are also discussed 相似文献
14.
HF radar data quality requirements for wave measurement 总被引：1，自引：0，他引：1
HF radar wave measurements are presented focussing on theoretical limitations, and thus radar operating parameters, and quality control requirements to ensure robust measurements across a range of sea states. Data from three radar deployments, off the west coast of Norway, Celtic Sea and Liverpool Bay using two different radar systems, WERA and Pisces, and different radio frequency ranges, are used to demonstrate the wave measurement capability of HF radar and to illustrate the points made. Aspects of the measurements that require further improvements are identified. These include modifications to the underlying theory particularly in high sea states, identification and removal of ships and interference from the radar signals before wave processing and/or intelligent partitioning to remove these from the wave spectrum. The need to match the radio frequency to the expected wave peak frequency and waveheight range, with lower radio frequencies performing better at higher waveheights and lower peak frequencies and vice versa, is demonstrated. For operations across a wide range of oceanographic conditions a radar able to operate at more than one frequency is recommended for robust wave measurement. Careful quality control is needed to ensure accurate wave measurements. 相似文献
15.
X-波段雷达近海海浪频谱反演的神经网络模型 总被引：2，自引：1，他引：1
X-波段雷达作为国内海浪观测的一种新工具,在海浪频谱获取和有效波高反演方面仍存在较多问题.本文利用非线性回归方法,将现场实测浮标数据频谱和雷达一维图像谱分别与标准频谱模型进行拟合,发现浮标频谱和一维图像谱具有标准频谱的特征,能够较准确地获取相应的谱参数.提出了建立由雷达一维图像谱参数反演海浪频谱参数的神经网络模型,同时在模型中加入影像序列信噪比,进而反演有效波高,并将反演结果与现场实测数据和传统算法(建立影像序列信噪比与有效波高之间的线性回归方程)进行了对比,结果表明,获取谱参数的误差和反演有效波高的平均误差在20％以内,而传统算法计算有效波高平均误差在20％以上. 相似文献
16.
Based mainly on TOGA COARE data, that is, the CI''D data from R/V Xiangyanghong No.5 (Pu et al.,1993),the temperature and current data from the Woods Hole mooring and other deep current data, the layered numerical profiles of buoyancy frequency and mean current components are figured out.A numerical method calculating internal wave dispersion relation without background shear current, used by Fliegel and Hunkins (1975),is improved to be fit for the internal wave equation with mean currents and their second derivatives.The dispersion relations and wave functions of the long crested internal wave progressing in any direction can be calculated inveniently by using the improved method.A comparison between the calculated dispersion relation in the paper and the dispersion relation in GM spectral model of ocean internal waves (Garret and Munk, 1972) is performed.It shows that the mean currents are important to the dispersion relation of internal waves in the western equatorial Pacific Ocean and that the currents make the wave progressing co-directional with (against) the currents stretched (shrink).The influence of the mean currents on dispersion relation is much stronger than that of their second derivatives, but that on wave function is less than that of their second derivatives.The influences on wave functions result in the change of vertical wavenumber, that is, making the wave function stretch or shrink.There exists obvious turning depth but no significant critical layer absorption is found. 相似文献
17.
Frequency management support for remote sea-state sensing using the JINDALEE skywave radar 总被引：1，自引：0，他引：1
Successful operation of a skywave (over-the-horizon, OTH) radar in a remote sea-state sensing mode is critically dependent upon the application of comprehensive frequency management techniques. In addition to the problem of selecting a frequency yielding an adequate signal-to-noise ratio in the geographical area under investigation, attention must be paid to minimization of ionospheric multimode and other phenomena capable of distorting or convoluting the sea backscatter spectrum. This paper describes the manner in which these problems have been addressed in the JINDALEE skywave radar, and relates the practical difficulties inherent in the task of frequency management in support of an OTH radar involved in sea-state sensing. Measurement techniques include backscatter and oblique-incidence sounding, HF spectral surveillance, and a low-powered frequency-agile "miniradar" capable of operating in either a conventional backscatter or alternate oblique-incidence mode. In addition to providing the main radar with real-time frequency management advice, a principal emphasis has been the acquisition of a synoptic data base suitable for off-line statistical analysis. 相似文献
18.
In this study the assimilation of HF radar data into a high resolution, coastal Wavewatch III model is investigated. An optimal interpolation scheme is used to assimilate the data and the design of a background error covariance matrix which reflects the local conditions and difficulties associated with a coastal domain is discussed. Two assimilation schemes are trialled; a scheme which assimilates mean parameters from the HF radar data and a scheme which assimilates partitioned spectral HF radar data. This study demonstrates the feasibility of assimilating partitioned wave data into a coastal domain. The results show that the assimilation schemes provide satisfactory improvements to significant wave heights but more mixed results for mean periods. The best improvements are seen during a stormy period with turning winds. During this period the model is deficient at capturing the change in wave directions and the peak in the waveheights, while the high sea state ensures good quality HF radar data for assimilation. The study also suggests that there are both physical and practical advantages to assimilating partitioned wave data compared to assimilating mean parameters for the whole spectrum. 相似文献
19.