Measurement of ocean wave spectra using a ship-mounted HF radar

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     

Measurement of ocean wave spectra using narrow-beam HE radar

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     

Very high-frequency radar mapping of surface currents

An ocean surface current radar (OSCR) in the very high frequency (VHF) mode was deployed in South Florida Ocean Measurement Center (SFOMC) during the summer of 1999. During this period, a 29-d continuous time series of vector surface currents was acquired starting on 9 July 1999 and ending 7 August 1999. Over a 20-min sample interval, the VHF radar mapped coastal ocean currents over a 7.5 km × 8 km domain with a horizontal resolution of 250 m at 700 grid points. A total of 2078 snapshots of the two-dimensional current vectors were acquired during this time series and of these samples, only 69 samples (3.3%) were missing from the time series. During this period, complex surface circulation patterns were observed that included coherent, submesoscale vortices with diameters of 2 to 3 km inshore of the Florida Current. Comparisons to subsurface measurements from moored and ship-board acoustic Doppler current profiles revealed regression slopes of close to unity with biases ranging from 4 to 8 cm s^-1 between surface and subsurface measurements at 3 to 4 m beneath the surface. Correlation coefficients were 0.8 or above with phases of - 10 to - 20° suggestive of an anticyclonic veering of current with depth relative to the surface current. The radar-derived surface current field provided spatial context for an observational network using mooring-, ship- and autonomous underwater vehicle-sensor packages that were deployed at the SFOMC     

Parametric estimation of ocean surface currents with HF radar

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     

基于PS-VF-TBD的地波雷达船只目标航迹起始方法

针对地波雷达低信噪比目标信号"闪烁"导致的航迹起始困难问题,本文提出了一种基于PS-VF-TBD的航迹起始方法.该方法综合利用了地波雷达回波谱中目标信号的展宽特征和运动特性,利用PS-VF-TBD方法对运动目标能量有效积累的特点,提高对疑似目标多帧信号间的关联概率,进而提高对真实目标的搜索概率和航迹起始成功率.通过地波...     

High-frequency ocean radar derived characteristics of sea surface currents in the Ariake Sea,Japan

Composite analysis was conducted using high-frequency radar data obtained during 2006–2015 in order to gain a better understanding of the current field in the Ariake Sea. The seasonally averaged surface current in the Ariake Sea was directed southward in all seasons, except around river mouths during summer. Heavy rainfall enhanced the outflow along the eastern coast of the Shimabara Peninsula from Isahaya Bay to the southern area 2–5 days after heavy rainfall. Spring–neap differences were clearly seen in the southward current along the Shimabara Peninsula. Interannual variation in the M₂ tidal current amplitude was synchronized with the lunar nodal cycle.     

单点高频地波雷达资料估算潮能耗散的方法（英文）

使用嵊泗站所布设的地波雷达观测获取的径向流数据,以及嵊泗、芦潮港、岱山3个潮汐观测站水位资料,采用两点近似投影方法反演流场全矢量流速,并用T_tide程序计算调和常数,分别计算O1、K1、M2、S2各分潮流速场及迟角场,并计算各点上的潮能通量及潮能耗散,得到嵊泗岛以西杭州湾口区域潮能耗散同地形存在良好对应关系,充分证明了采用地波雷达观测数据进行潮能耗散计算这一方法的可行性,供相关工作者作进一步研究和讨论。     

单点高频地波雷达资料估算潮能耗散的方法

使用嵊泗站所布设的地波雷达观测获取的径向流数据,以及嵊泗、芦潮港、岱山3个潮汐观测站水位资料,采用两点近似投影方法反演流场全矢量流速,并用T-Tide程序计算调和常数,分别计算O1、K1、M2、S2各分潮流速场及迟角场,并计算各点上的潮能通量及潮能耗散,得到嵊泗岛以西杭州湾口区域潮能耗散同地形存在良好对应关系,充分证明了采用地波雷达观测数据进行潮能耗散计算这一方法的可行性,供相关工作者作进一步研究和讨论.     

Determination of instantaneous sea surface,wave heights,and ocean currents using satellite observations of the global positioning system

Abstract

Using GPS phase observations in the kinematic mode, we are able to achieve centimeter accuracy in relative three‐dimensional coordinates. This could be verified even for fast‐moving sensors in aircraft, such as airborne photogrammetric cameras, at the time of exposure. Sophisticated kinematic software has been developed resolving cycle slips and carrier‐phase ambiguities during motion. To determine the instantaneous sea surface, the GPS receiver is placed in a free‐drifting buoy with the antenna on top. Differencing the 1‐Hz observations, wave heights can be determined as well as velocity and direction of ocean (tidal) currents.

This article deals with the experiences from a test for the practical realization of this proposal. Hardware installation, software, and data analysis are described. Plans to use such an observational scenario of a GPS buoy array in the North Sea for the calibration of the radar altimeter of the European satellite ERS‐1 are presented.     

舟山海域高频地波雷达表层流探测试验

2015年4月7-30日,在浙江省舟山近海海域开展了“嵊山-朱家尖”小型阵列变频高频地波雷达系统的海上比测试验,通过雷达观测数据与定点ADCP海流资料的比对检验了地波雷达表层流探测性能。径向流比对结果显示,测点与雷达法向夹角越小,距离雷达距离越近,径向流比测结果越好,雷达探测的结果越可靠。嵊山站径向流与ADCP观测结果的各站总体平均误差为7.98 cm/s,平均均方根误差为15.34 cm/s,平均相关系数为0.89,朱家尖站径向流与ADCP观测结果的各站总体平均误差为6.24 cm/s,平均均方根误差为12.36 cm/s,平均相关系数为0.81。根据矢量流比对结果显示,矢量流速与ADCP观测结果的各站总体平均误差为4.82 cm/s,平均均方根误差为15.03 cm/s,平均相关系数为0.44。设置在嵊山、朱家尖两个雷达站双站探测的核心区域（两个雷达站连线的中垂线上,并且与两个雷达站构成一个近似直角三角形）的站点比测结果更加理想,当流速大于0.25 m/s时,对于核心区域平均后的流向均方根误差为24.9°。     

Measurement of ocean surface winds using synthetic aperture radars

A methodology for retrieving high-resolution ocean surface wind fields from satellite-borne synthetic aperture radar (SAR) data is introduced and validated. The algorithms developed are suited for ocean SAR data, which were acquired at the C band of either vertical (VV) or horizontal (HH) polarization in transmission and reception. Wind directions are extracted from wind-induced streaks that are visible in SAR images of the ocean at horizontal scales greater than 200 m. These wind streaks are very well aligned with the mean surface wind direction. To extract the orientation of these streaks, two algorithms are introduced, which are applied either in the spatial or spectral domain. Ocean surface wind speeds are derived from the normalized radar cross section (NRCS) and image geometry of the calibrated SAR images, together with the local SAR-retrieved wind direction. Therefore, several C-band models (CMOD IFR2, CMOD4, and CMODS) are available, which were developed for VV polarization, and have to be extended for HH polarization. To compare the different algorithms and C-band models as well as demonstrate their applicability, SAR-retrieved wind fields are compared to numerical-model results considering advanced SAR (ASAR) data from Environmental Satellite (ENVISAT), a European satellite.     

基于AIS信息校准的双频地波雷达的船只融合跟踪

高频地波雷达（HFSWR）和自动船只确认系统（AIS）是船只跟踪的重要传感器。高频地波雷达可以用来跟踪探测区域的所有船只,而AIS只能用来确认合作船只的信息。由于海杂波的干扰,使用单频率地波雷达的船只跟踪会淹没在布拉格峰值的盲区里,改变探测频率是克服这一缺点的有效手段。在这种背景下,我们提出一种基于AIS校准的双频雷达融合探测算法。因为不同频率的地波雷达测量与AIS的测量值存在系统误差,所以AIS信息可以用来估计和校准地波雷达的每个频率的系统误差。首先,将合作目标的点迹测量与地波雷达的点迹测量通过JVC分配算法进行点迹关联。从合作船只的点迹关联结果中,双频雷达的系统误差可以估计和校准。其次,基于校准的双频雷达数据,使用融合JPDA-UKF算法进行船只跟踪。通过真实探测的数据的实验结果显示所提算法可以实时跟踪船只,相比单频率跟踪可以进一步提高跟踪能力和跟踪精度。     

Coupling winds to ocean surface currents over the global ocean

A Wind stress–Current Coupled System (WCCS) consisting of the HYbrid Coordinate Ocean Model (HYCOM) and an improved wind stress algorithm based on Donelan et al. [Donelan, W.M., Drennan, Katsaros, K.B., 1997. The air–sea momentum flux in mixed wind sea and swell conditions. J. Phys. Oceanogr. 27, 2087–2099] is developed by using the Earth System Modeling Framework (ESMF). The WCCS is applied to the global ocean to study the interactions between the wind stress and the ocean surface currents. In this study, the ocean surface current velocity is taken into consideration in the wind stress calculation and air–sea heat flux calculation. The wind stress that contains the effect of ocean surface current velocity will be used to force the HYCOM. The results indicate that the ocean surface velocity exerts an important influence on the wind stress, which, in turn, significantly affects the global ocean surface currents, air–sea heat fluxes, and the thickness of ocean surface boundary layer. Comparison with the TOGA TAO buoy data, the sea surface temperature from the wind–current coupled simulation showed noticeable improvement over the stand-alone HYCOM simulation.     

基于高频地波雷达的多时间尺度海流研究

近海海流受多种动力过程及岸线岛屿的作用呈现空间和时间尺度上的复杂变化,而地波雷达由于其探测面积广、时间分辨率高的特点成为研究这些变化的有效手段。本文利用舟山海域多年高频地波雷达资料,通过潮流调和分析、低通滤波和相关性分析对该海域海流潮周期、极端事件、季节、年际尺度的动力过程进行了解译。研究表明,舟山海域属于正规半日潮,潮流运动形式以顺时针旋转流为主,流速大小在空间上为东北方向较大,往西南方向逐渐减小,并在近岸处得到增强。余流的年际变化并不显著,但存在着明显的季节变化,例如冬季为南向流,流速减小,空间分布上近岸较外海大,而夏季与之反向,为北向流,流速较大,空间分布较为均匀。进一步分析了风与余流之间的相关性,在大风期间,风与余流的速度相关系数在0.48～0.90之间,方向相关系数在0.55～0.68之间。极端事件发生时,速度、方向的相关系数分别高达0.92与0.91。总体而言,通过分析高频地波雷达数据能够较好地反映舟山海域海流的时空特征,为海洋灾害监测和污染物、藻华的输运研究提供依据。     

Models of radar imaging of the ocean surface waves

A number of models which would explain ocean wave imagery taken with a synthetic aperture imaging radar are analyzed analytically and numerically. Actual radar imagery is used to support some conclusions. The models considered correspond to three sources of radar backscatter cross section modulation: tilt modulation, roughness variation, and the wave orbital velocity. The effect of the temporal changes of the surface structure, parametric interactions, and the resulting distortions are discussed.     

基于高频地波雷达资料的海南中东部近海表层海流特征

利用海南中东部近海海域高频地波雷达观测得到的2019年4月—2020年3月表层海流资料进行潮流调和分析和余流分析。结果表明: 海南中东部近海海域以不规则半日潮流为主, 半日分潮M₂和S₂以往复流为主, 全日分潮O₁、K₁以顺时针旋转流为主, M₂、S₂、O₁、K₁分潮最大潮流流速的比为1 : 0.51 : 0.60 : 0.65, M₂为最主要分潮。最大可能潮流流速分布从西南方向向东北方向逐步增大, 最大值为35cm·s^-1。余流受东亚季风影响较大, 季节变化特征显著, 呈夏季形态(6月—8月)、冬季形态(9月—次年2月)和过渡形态(3月—5月)。夏季形态流向东北, 平均流速29cm·s^-1; 冬季形态持续时间最长, 流向西南, 平均流速36cm·s^-1, 大于夏季形态; 过渡形态为冬季形态向夏季形态的转变期, 流向分布较复杂, 平均流速13cm·s^-1, 明显小于夏季和冬季形态。从全年来看, 西南向流动的时间最长、流速最大, 海南中东部表层海水物质输运自东北向西南。     

Line broadening on HF ocean surface radar backscatter spectra

Experimental results from an array of moored current meters and an HF ocean surface radar support the idea that line broadening on the radar spectra is caused by the velocity distribution within the radar target cell. The experiment was done in the wake of a small island where the velocity variations were severe. An estimate is made of the line broadening which can be expected. In a turbulent flow with dissipation rate of the orderepsilon sim 10^{-10}m^{2}s^{-3}and target cell size 1 3000 m, the line broadening isDeltaf sim 10^{-3}Hz. This would be resolved with a radar time series ofsim 20min and indicates that the HF ocean surface radar technique has potential in the observation of surface velocity distributions.     

海洋内波ADCP监测技术研究

海洋内波与声场的相互关系是一个十分重要的研究课题.内波是影响声信道特征的重要因素;反之,受内波影响的声场也包含着海洋内波动力过程的信息.针对二者之间的关系,从工程的角度上介绍了利用声学多普勒海流剖面仪(ADCP)对海洋内波进行监测的原理和方法,并结合实际的海试情况给出声学多普勒海流剖面仪对海洋内波的监测结果,验证了方法的有效性.     

On the synthetic aperture radar imaging of ocean surface waves

A process of synthetic aperture radar imaging of ocean surface waves is considered on the basis of the two-scale model of microwave scattering by a disturbed sea surface. Analytical expressions are obtained to relate characteristics of a large-scale wave image, averaged over an ensemble of realizations of the small-scale ripple, with the wave, radar, and viewing scheme as parameters. It is shown that the wave image would be defocused as an image of a target moving in the along-track direction with a speed equal to a half of the wave phase speed projection on the line of flight. The defocusing magnitude was measured experimentally for the ocean swells images, obtained with an airborneS-band radar, and the results are found to be in satisfactory agreement with the model prediction.