共查询到20条相似文献，搜索用时 15 毫秒
1.
Bass F. Braude S. Fuks I. Kalmykov A. Megn A. Ostrovsky I. Rosenberg A. 《Oceanic Engineering, IEEE Journal of》1977,2(1):43-52
Experiments on the scattering of radio waves in the range 200 m to 3 cm from a rough sea surface are described. Amplitude, frequency, and space-time characteristics of scattered radio signals at different states of the sea surface are presented. It is shown that the problem of the short and medium wave scattering from the sea can be solved by the perturbance method. In this case the mechanism of scattering is of "resonant" character. The intensity of the backscatter signals is proportional to the density of the spatial spectrum on the half-length of the radio waves. The high frequency radio wave scattering is well described by a two-scale model of the scattering surface, "ripple on the large wave." The intensity of scattered radio signals is also proportional to the spectrum density of "ripples" whose length is approximately equal to half a radio wave. The effect of the large waves is to modulate the amplitude of a scattered radio signal and to broaden its frequency spectrum. Methods of solution of the reverse problem were considered. This allowed determination of parameters of sea roughness by characteristics of scattered radio signals. The principles of design of the corresponding equipment are described. 相似文献
2.
A tide height measurement technique usingS -band radio waves in an oblique incidence interferometer is reviewed. Generalization of the technique is described which reduces the required bandwidth of the radio frequency adjustment and increases its efficiency. This generalization, however, introduces an ambiguity in the height determination and also requires specification of the phase shift of the radio waves specularly reflected from the sea surface. The ambiguity is shown to be easily removable given coarse information about the expected time derivative of tidal height. The influence of the phase shift which contains sea-wave information is studied analytically and requirement in its specification is evaluated to have an accuracy ofpm1deg . This corresponds to a tide height determination accuracy ofpm1 cm. The method is designed for coastal regions where a bistatic experiment geometry is feasible. 相似文献
3.
Radio signals of decameter wavelength resonantly scattered from waves on the sea surface are used to measure precisely the wavelength, frequency, and direction of travel of those waves. These measurements are not only important in themselves, but are also used to deduce currents, winds, and perhaps wind stress at the sea surface. Techniques for obtaining these measurements, as well as experiments to evaluate these techniques are discussed. Finally, scatter has been used to produce the first high-resolution measurements of the directional distribution of large ocean waves, measurements of ocean surface currents at ranges of 20 km, and of surface winds at ranges of 3000 km. 相似文献
4.
V. G. Bondur V. A. Dulov A. B. Murynin V. Yu. Ignatiev 《Izvestiya Atmospheric and Oceanic Physics》2016,52(6):637-648
A method to register sea-wave spectra using optical aerospace imagery has been developed. The method is based on the use of retrieval operators both in areas of high and low spatial frequencies, including the areas of spectral maximum. The approach to adjust and validate the method developed using sea truth data obtained by string wave recorders has been suggested. This paper presents the results of using the suggested method to study sea-wave spectra using high-resolution satellite imagery for various water areas under different conditions of wave generation. 相似文献
5.
Kelvin wake is one of the common wakes generated by moving ships and contains rich information about ships. In this paper, free wave elevations of Kelvin wake are calculated based on the Michell thin ship theory combined with a point source perturbation model. The probability density function of sea surface slopes is introduced to calculate the specular reflection of sunlight and skylight and the refraction of scattered light underwater. Satellite-detected Kelvin wakes are then simulated by adding surface specular reflectance and water-leaving reflectance. Simulation results agree well with satellite measurements. The specular reflection of sunlight is the decisive factor affecting the features of Kelvin wakes according to the simulation results. The main factors that influence the specular reflection of sunlight, such as the incident direction and observation direction, ship parameters, and background environment, are discussed. This study is helpful for wake detection and provides a preliminary theoretical method for the retrieval of ship information. 相似文献
6.
海面电磁回波频谱宽度与海浪波高密切相关，可应用频谱宽度进行海浪有效波高反演。本文应用线性滤波法仿真出了海表散射面元在雷达视向上的投影速度，建立了回波谱宽模型，分析了雷达空间分辨率、回波时间序列长度及海洋环境参数等因素对频谱宽度的影响，同时还针对如何在实际观测过程中选择回波时间序列长度、观测方位角等参数进行了讨论。最后还将理论结果与CSIR-X波段雷达实测数据谱宽估计结果进行了比较。结果表明，剔除雷达噪声以及频率泄露的影响后，基于高斯分布标准偏差的谱宽估计方法所得结果与理论结果吻合很好，这从而证明了理论结果的可靠性。本文所得结果对海浪有效波高反演具有一定参考价值。 相似文献
7.
An approach to the retrieval of sea wave spatial spectra based on satellite optical imagery in linear and nonlinear approximations is described. Physical mechanisms of the formation of disturbed sea surface brightness fields recorded by remote sensing equipment are analyzed. Wave spectra retrieval methods using brightness field formation models that consider linear and nonlinear dependencies on sea surface slopes are suggested. A method for the construction of operators that retrieve the spatial spectra of surface wave slopes and elevations from aerospace imagery and take into account nonlinear modulations of disturbed sea surface brightness fields is developed. This method is based on the numerical simulation of sea surface images and the construction of a retrieving operator with respect to a set of parameters determined by aerospace imaging conditions. Examples of the use of the developed methods are given. 相似文献
8.
北极海冰的年代际转型与中国冻雨年代际变化的关系 总被引：1，自引：0，他引：1
基于1961-2013年HadISST海冰密集度资料,定义了北极海冰的季节性融冰指数,结果显示近几十年来北极季节性融冰范围呈显著的上升趋势,并分别在20世纪70年代末和90年代中期存在显著的年代际转型,相应地,中国冻雨发生频数总体上呈现出显著的减少趋势,但也存在显著的年代际转型。在20世纪70年代末之前,北极季节性融冰范围较小但显著增长,中国冻雨频数年际变化振幅较大,且主要受巴伦支海、喀拉海海冰的影响;20世纪70年代末至90年代中期北极季节性融冰范围维持振荡特征,没有显著的线性趋势,中国冻雨频数变化振幅减小,与北极海冰相关较弱,主要相关因子为北大西洋及北太平洋海表温度变化;而90年代中期以后,北极海冰融化加快,特别是2007年以后,季节性融冰范围大大增加,而中国冻雨频数处于低发时段,其变化与太平洋扇区海冰及堪察加半岛附近海温呈显著负相关,季节性融冰的显著区域也从东西伯利亚海逆时针旋转向波弗特海-加拿大群岛北部扩张,同时向北极中央区扩张。不同年代影响冻雨的海温或海冰关键海区不同,产生特定的大气环流异常响应,进而影响到我国冻雨。 相似文献
9.
《Oceanic Engineering, IEEE Journal of》1996,21(1):24-36
The treatment of acoustic energy forward scattered from the sea surface, which is modeled as a random communications scatter channel, is the basis for developing an expression for the time-dependent coherence function across a vertical receiving array. The derivation of this model uses linear filter theory applied to the Fresnel-corrected Kirchhoff approximation in obtaining an equation for the covariance function for the forward-scattered problem. The resulting formulation is used to study the dependence of the covariance on experimental and environmental factors. The modeled coherence functions are then formed for various geometrical and environmental parameters and compared to experimental data 相似文献
10.
An analysis of the radar backscattering from the ocean surface covered by oil spill is presented using a microwave scattering model and Monte-Carlo simulation. In the analysis, a one-dimensional rough sea surface is numerically generated with an ocean waveheight spectrum for a given wind velocity. A two-layered medium is then generated by adding a thin oil layer on the simulated rough sea surface. The electric fields backscattered from the sea surface with two-layered medium are computed with the method of moments (MoM), and the backscattering coefficients are statistically obtained with N independent samples for each oil-spilled surface using the Monte-Carlo technique for various conditions of surface roughness, oil-layer thickness, frequency, polarization and incidence angle. The numerical simulation results are compared with theoretical models for clean sea surfaces and SAR images of an oil-spilled sea surface caused by the Hebei (Hebei province, China) Spirit oil tanker in 2007. Further, conditions for better oil spill extraction are sought by the numerical simulation on the effects of wind speed and oil-layer thickness at different incidence angles on the backscattering coefficients. 相似文献
11.
在对海洋监视监测的过程中,高频地波雷达的船只目标检测能力与其对海杂波的抑制能力密切相关。但是,传统海杂波时域抑制方法存在目标回波参数与海杂波相近时难以区分其各自分量,对消时目标被误消除的问题。针对上述问题,本文提出了一种适用于高频地波雷达海杂波的边界约束循环对消方法。该方法综合海杂波频移理论和实际海杂波特性分析制定出边界条件,约束建模对消过程,实现海杂波分量的抑制。实测地波雷达数据和船舶自动识别系统(AIS)数据检验的结果表明,本文方法克服了传统方法的不足且信杂比改善更加稳定,能够更加有效地实现海杂波循环对消。 相似文献
12.
G. N. Khristoforov A. S. Zapevalov V. E. Smolov Yu. R. Feldman 《Physical Oceanography》1994,5(6):461-468
The results of lidar sensing of the sea surface carried out from an oceanographic platform in the Black Sea under different hydrometeorological conditions are considered. It is found that the frequency, time, and intensity of the mirror-reflected lidar specks of light vary essentially when the wind wave structure anomalies appear, which arise owing to some physical processes evolving in the air-sea boundary layers. The effects conditioned by an unsteady and non-uniform wind, the hydrological front, the slicks related to internal waves and Langmuir circulation, industrial pollution of the sea surface by surface-active substances, and rainfall are estimated quantitatively. A conclusion about the prospects of application of the lidar specks indication method for ecological monitoring and control of the sea surface state and internal basins is drawn.Translated by Mikhail M. Trufanov. 相似文献
13.
Kohtaro Hosoda 《Journal of Oceanography》2010,66(4):439-473
Satellite-based microwave radiometers can measure sea surface temperature (SST) over wide areas, even under cloud cover, owing
to the weak absorption of microwaves by cloud droplets. This advantage is not available in the case of infrared observations,
hence SST data derived from microwave radiometers have been widely used for operational and research purposes in recent years.
This paper reviews the significant algorithms, validations, and applications related to microwave observation of SST. The
history and specifications of past and present microwave radiometers are also documented. Various physical properties, including
sea surface salinity, sea surface wind, molecules in the atmosphere, and clouds, affect the accuracy of SST data estimated
by satellite-based microwave radiometers. Estimation algorithms are designed to correct these effects by using microwave measurements
in several frequency channels and by using data of ancillary geophysical parameters. Validation studies have shown that microwave
radiometer SST data have high accuracy that is comparable to the accuracy of data obtained from infrared measurements. However,
certain persistent problems, such as sea-surface wind correction, remain to be solved. 相似文献
14.
基于一维综合孔径微波辐射计的海面温度反演研究 总被引：1，自引：0，他引：1
Due to the low spatial resolution of sea surface temperature(T_S) retrieval by real aperture microwave radiometers,in this study, an iterative retrieval method that minimizes the differences between brightness temperature(T_B)measured and modeled was used to retrieve sea surface temperature with a one-dimensional synthetic aperture microwave radiometer, temporarily named 1 D-SAMR. Regarding the configuration of the radiometer, an angular resolution of 0.43° was reached by theoretical calculation. Experiments on sea surface temperature retrieval were carried out with ideal parameters; the results show that the main factors affecting the retrieval accuracy of sea surface temperature are the accuracy of radiometer calibration and the precision of auxiliary geophysical parameters. In the case of no auxiliary parameter errors, the greatest error in retrieved sea surface temperature is obtained at low T_S scene(i.e., 0.710 6 K for the incidence angle of 35° under the radiometer calibration accuracy of0.5 K). While errors on auxiliary parameters are assumed to follow a Gaussian distribution, the greatest error on retrieved sea surface temperature was 1.330 5 K at an incidence angle of 65° in poorly known sea surface wind speed(W)(the error on W of 1.0 m/s) over high W scene, for the radiometer calibration accuracy of 0.5 K. 相似文献
15.
Sonar and radar signals are scattered by small-scale roughness elements of the sea surface. The characteristics of the roughness depend on wind, sea state, and other parameters. The dynamic behavior of this roughness is related to radar backscatter. This provides a basis for oceanographic radar remote sensing and links radar backscatter to sea surface sonar conditions. Radar, sonar, and roughness experiments have been conducted at the research platform NORDSEE. The results are combined and provide a method to estimate shallow water sonar conditions from the radar backscatter cross section 相似文献
16.
南海海面高度变化及其与太平洋上涛动信号的关系 总被引：1，自引：1，他引：0
本文使用循环平稳经验正交函数(CSEOF)方法分析了南海海面高度(SCS-SSH)的时空变化模态,并对它们与太平洋海盆尺度振荡的关系进行了探讨分析。结果表明,SCS-SSH的第一个CSEOF模态是季节变化模态,其变化强度受到一个与厄尔尼诺-南方涛动(ENSO)有关的低频信号的调制,即在厄尔尼诺期间季节变化的幅度减弱(最大可降低30%,1997/98)而在拉尼娜期间季节变化增强。SCS-SSH的第二个CSEOF模态是年际-年代际尺度的低频变化模态,其空间模态的月与月之间的差异微弱,而时间模态和太平洋年代际振荡(PDO)指数高度相关。然后,我们使用独立成分分析(ICA)方法提取了太平洋中的五个主要振荡成分,并检验了它们对SCS-SSH变化的各自影响。分析表明,纯粹的ENSO模态(类似于太平洋东部型ENSO)对SCS-SSH的低频变化的影响比较微弱,而ENSO的红化模态(类似于太平洋中部型ENSO)对SCS-SSH的低频变化具有明显影响。由于ENSO的红化模态是PDO信号的一个主要成分,这一结果解释了为什么在影响SCS-SSH的低频变化上PDO比ENSO更重要。径向鞍型振荡模态、黑潮延伸体处的增温模态、以及赤道的降温模态也由ICA方法提取出来,但它们对SCS-SSH低频变异的影响微弱。进一步的分析表明,太平洋的涛动信号可能以不同的方式来影响南海海面高度变化和海表温度变化。 相似文献
17.
Deterministic sea-wave prediction (DSWP) models are appearing in the literature designed for quiescent interval prediction in marine applications dominated by large swell seas. The approach has focused upon spectral methods which are straightforward and intuitively attractive. However, such methods have the disadvantage that while the sea is aperiodic in nature, the standard discrete spectral processing techniques force an absolutely periodic structure onto the resulting sea surface prediction models. As it is the shape of the sea surface that is important in such applications, particularly near the end of the domain which is important, the standard windowing techniques used in signal processing work to reduce leakage artifacts cannot be employed. This has necessitated the use of end matching methods that can be both inconvenient and may reduce the fraction of the time for which legitimate predictions are available. As a result, an investigation has been undertaken of the use of finite impulse response prediction filters to provide the necessary dispersive phase shifting required in DSWP systems. The present work examines the theoretical basis for such filters and explores their properties together with their application to both long and short crested swell seas. It is shown that wide band forms of such filters are only convergent in the sense of distributions having both infinite duration impulse responses and asymptotically divergent first derivatives. However, appropriate band limitation can produce useful finite impulse responses allowing implementation via standard discrete convolution methods. It is demonstrated that despite the prediction filters having a non-causal impulse response such filters can be used in practice due to a combination of the asymmetric nature of the impulse response and the fundamental nature of the prediction process. The findings are confirmed against actual sea-wave data. 相似文献
18.
基于Hough变换原理的海冰厚度识别方法 总被引：1，自引：1，他引：0
作为主要海冰参数之一的海冰厚度对海冰灾害评估和极地船舶与冰区海洋工程结构设计具有重要意义。采用船侧视频图像对海冰厚度进行自动识别是提取海冰参数的重要方式。本文采用基于Hough变换的机器视觉方法对海冰翻转过程中的表面轮廓线进行识别,从而自动获取海冰厚度参数。根据海冰图像特征制定了图像边缘识别?近似线段识别?海冰轮廓线段组识别的计算流程。在线段组识别过程中,根据海冰的几何特征建立了由夹角、长度及间距参数相关联的3个识别参数所组成的判断条件。为验证方法的可靠性,将该方法用于“雪龙”号第八次北极科考的走航实测数据中,结果表明,3个识别参数均具有最优阈值。当低于最优值时提高阈值可增加有效识别率;而高于最优值时提高阈值则会导致误判率增大,采用最优阈值可使冰厚识别率达到90%以上。因此,采用基于Hough变换的冰厚识别方法可实现对海冰厚度的实时监测。 相似文献
19.
20.
海杂波微弱目标分形检测 总被引：1，自引：1，他引：0
The target on the sea surface is complex and difficult to detect due to the interference of backscattered returns from the sea surface illuminated by the radar pulse. Detrended fluctuation analysis （DFA） has been used successfully to extract the time-domain Hurst exponent of sea-clutter series. Since the frequency of the sea clutter mainly concentrates around Doppler center so that we consider to extract frequency-do- main fractal characterization and then detect a weak target within sea clutter by using the difference of frequency-domain fractal characterization. The generalized detrended fluctuation analysis （GDFA） is more flexible than traditional DFA owing to its smoothing action for the clutters. In this paper, we apply the GDFA to evaluate the generalized Hurst exponent of sea-clutter series in the frequency domain. The difference of generalized Hurst exponents between different sea-clutter range bins would be used to determine whether the target exists. Moreover, some simulations with the real IPIX radar data have also been demonstrated in order to suooort this conclusion. 相似文献