共查询到20条相似文献，搜索用时 15 毫秒
1.
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
2.
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
3.
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
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浪向代表着海浪传播方向,它是海上交通安全以及海岸资源管理的重要海洋环境参数之一。本文针对X波段测波雷达对海杂波的连续成像,提出了一种基于光流法的海浪传播方向反演新方法。该方法利用X波段测波雷达接收的海面回波图像序列直接进行光流运动估计,将得到的每个像素点的运动矢量进行加权平均,最后得到实际的海浪传播方向。与传统基于频域的X波段测波雷达浪向反演方法相比,本文提出的方法直接从时域来进行回波信号处理,无需提前得到调制传递函数以及精确的海流,减少了由于海流估算的不准确以及调制传递函数选取的误差而给雷达浪向反演带来的影响。同时,该方法简单高效,占用资源少,将其应用至仿真雷达回波以及现场实测数据来进行浪向反演,反演得到的浪向与仿真设定浪向值以及浮标实时观测浪向结果都有很好的吻合度,变化趋势也完全一致,进而验证了该方法的有效性以及准确性。 相似文献
6.
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
7.
Naoto Ebuchi Yasushi Fukamachi Kay I. Ohshima Kunio Shirasawa Masao Ishikawa Toru Takatsuka Takaharu Daibo Masaaki Wakatsuchi 《Journal of Oceanography》2006,62(1):47-61
Three High Frequency (HF) ocean radar stations were installed around the Soya/La Perouse Strait in the Sea of Okhotsk in order
to monitor the Soya Warm Current (SWC). The frequency of the HF radar is 13.9 MHz, and the range and azimuth resolutions are
3 km and 5 deg., respectively. The radar covers a range of approximately 70 km from the coast. The surface current velocity
observed by the HF radars was compared with data from drifting buoys and shipboard Acoustic Doppler Current Profilers (ADCPs).
The current velocity derived from the HF radars shows good agreement with that observed using the drifting buoys. The root-mean-square
(rms) differences were found to be less than 20 cm s−1 for the zonal and meridional components in the buoy comparison. The observed current velocity was also found to exhibit reasonable
agreement with the shipboard ADCP data. It was shown that the HF radars clearly capture seasonal and short-term variations
of the SWC. The velocity of the Soya Warm Current reaches its maximum, approximately 1 m s−1, in summer and weakens in winter. The velocity core is located 20 to 30 km from the coast, and its width is approximately
40 km. The surface transport by the SWC shows a significant correlation with the sea level difference along the strait, as
derived from coastal tide gauge records at Wakkanai and Abashiri.
Deceased. 相似文献
8.
An Empirical Method to Derive Ocean Waves From Second-Order Bragg Scattering: Prospects and Limitations 总被引：2，自引：0，他引：2
Klaus-Werner Gurgel Heinz-Hermann Essen Thomas Schlick 《Oceanic Engineering, IEEE Journal of》2006,31(4):804-811
High-frequency (HF) radar wave processing is often based on the inversion of the Barrick-Weber equations, introduced in 1977. This theory reaches its limitations if the length of the Bragg-scattering wave raises to the order of the significant waveheight, because some assumptions are no longer met. In this case, the only solution is moving to lower radar frequencies, which is not possible or desirable in all cases. This paper describes work on an empirical solution which intends to overcome this limitation. However, during high sea state, the first-order Bragg peaks sometimes could not be clearly identified which avoids the access to the second-order sidebands. These cases cause problems to the algorithm which have not been solved yet and currently limit the maximum significant waveheight to about the same values as reported for the integral inversion method. The regression parameters of the empirical solution calibrated from the European Radar Ocean Sensing (EuroROSE) data set are constant values for the complete experiment and when applied to the HF radar data they reconstruct the measurements by a colocated wave buoy quite well. When including a radar-frequency-dependent scaling factor to the regression parameters, the new algorithm can also be used at different radar frequencies. The second-order frequency bands used for the empirical solution are sometimes disturbed by radio interference and ship echoes. Investigations are presented to identify and solve these situations 相似文献
9.
We propose a new analytical algorithm for the estimation of wind speeds from altimeter data using the mean square slope of
the ocean surface, which is obtained by integration of a widely accepted wind-wave spectrum including the gravity-capillary
wave range. It indicates that the normalized radar cross section depends not only on the wind speed but also on the wave age.
The wave state effect on the altimeter radar return becomes remarkable with increasing wind speed and cannot be neglected
at high wind speeds. A relationship between wave age and nondimensional wave height based on buoy observational data is applied
to compute the wave age using the significant wave height of ocean waves, which could be simultaneously obtained from altimeter
data. Comparison with actual data shows that this new algorithm produces more reliable wind speeds than do empirical algorithms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
高频地波雷达生成海洋表面矢量流图 总被引：10，自引：0，他引：10
武汉大学研制的双站高频地波雷达系统OSMAR2000利用测得的两幅单站径向海流图生成矢量海流图。经典矢量流图生成方法不能直接应用到OSMAR2000系统中。本文提出一种先在极坐标系下用自然三次样条函数将径向流插值到公共网格上然后直接进行矢量合成的矢量海流图生成方法。OSMAR2000在东海的表面矢量流实测结果与作对比验证的传统海流计测量结果十分吻合。对比数据表明，该方法是可行的，且优于先进行径向流线性插值后矢量合成的矢量流图生成方法。这也是国内首次利用高频地波雷达实现海洋表面矢量流的实时监测。 相似文献
11.
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
12.
本文首先对合成孔径雷达（SAR）海浪成像中的3种调制（倾斜调制、流体力学调制与速度聚束调制）的影响进行了对比分析,结果显示:速度聚束调制对SAR图像的影响最为显著。另外,由于SAR图像中固有相干斑噪声的存在,较低波数范围的噪声难以滤除或抑制,利用经典MPI方法反演海浪谱会造成低波数范围谱值偏大。基于此,本文借鉴经典MPI海浪谱反演算法,建立了基于速度聚束调制的海浪方位向斜率谱和有效波高的反演算法。通过将经典MPI方法、同极化调制法及本文算法等3种海浪反演方法所得有效波高与浮标数据进行比较,结果显示:本文方法反演得到的海浪有效波高与浮标数据获得的有效波高之间的均方误差为0.79 m,为3种方法中最小。 相似文献
13.
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
14.
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
15.
This study represents an attempt to quantitatively assess the capability of a spaceborne radar altimeter to infer ocean surface wind speeds from a measurement of the backscattered power at vertical incidence. The study uses data acquired during 184 near overflights of NOAA data buoys with the GEOS-3 satellite radar altimeter and encompasses a wind-speed range from less than 1 to 18 m/s. An algorithm is derived from the data comparison for converting measurements of the normalized scattering cross section of the ocean surface at 13.9 GHz into estimates of the surface wind speed at the standard anemometer height of 10 m. The algorithm is straightforward and potentially useful for on-board processing of raw altimeter data for the purpose of providing real-time estimates of surface wind speed. For winds in the range of 1 to 18 m/s, the mean difference between the altimeter-inferred winds and the buoy measurements is negligible while the standard deviation of the difference is 1.74 m/s. 相似文献
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风速是重要的海洋状态参数之一,对海面风速的准确提取是实现海洋环境监测和沿海工程应用的重要保证。目前,作为新兴海洋环境监测设备,高频雷达在风速提取方面仍然存在挑战。本文提出了一种基于人工神经网络的风速提取方法,利用历史浮标测量海态数据训练风速提取网络,实现风速与有效波高、波周期、风向及时间因素之间的非线性映射。测试结果表明了这一网络在时间和空间上的稳定性;进而将已训练的网络应用到便携式高频地波雷达OSMAR-S的风速反演中,得到的风速与浮标测量风速间的相关系数达到0.849,均方根误差为2.11 m/s。这一结果明显优于常规由浪高反演风速的SMB方法,验证了该方法在高频雷达风速反演中的可行性。 相似文献
18.
D. V. Ivonin V. A. Telegin P. V. Chernyshov S. A. Myslenkov S. B. Kuklev 《Oceanology》2016,56(4):591-600
We present the results of development and testing of a coastal X-band radar system for monitoring wind waves and currents at the Black Sea (near Gelendzhik) created on the basis of nautical radars. Radar measurements of wave heights were validated by data from a wave buoy and a moored acoustic Doppler current profiler (ADCP). The conditions for successful radar measurements of waves in the coastal environment have been determined. It was shown that a radar with an aperture 1° could successfully measure wave heights at a distance of 1.2 km from the radar, when waves arrive at an angle of ±31° to the main sensing direction. In this case, for wave height measurements, the correlation coefficient between the radar and independent data is 0.82 and the standard deviation is 0.26 m. 相似文献
19.
A. K. Laing 《Applied Ocean Research》1992,14(6):341-351
A spectral ocean wave model with explicit representations of the identified physical source terms is described. The model has the ability to represent the evolution of the wave spectrum effectively without the need for a very short integration timestep. This is achieved by incorporating a simple parameterisation for the weakly nonlinear wave-wave interactions and using a predictor step to estimate the integral parameters which govern the form of this function. The model was tested over a number of ideal situations and conformed well to the data. It also performed comparably to the third-generation WAM model. In field trials the model was driven by winds derived from numerical weather prediction model initialisations via a diagnostic marine boundary layer model. The wave estimates were compared with data from a Waverider buoy at a site exposed to the Southern Oceans. Significant wave heights were modelled well with a root-mean-square error of 0·9m and a scatter index of 0·24. Frequency characteristics produced poorer results but similar to other operational models, i.e. frequency was over-estimated. Comparisons with significant wave heights from the GEOSAT radar altimeter gave a spatial measure of the model's performance which was similar to the temporal measure from the Waverider buoy data. 相似文献