Contrast validation test for retrieval method of high frequency ground wave radar

In this paper, on the basis of the working principles of high frequency ground wave radar for retrieval of ocean wave and sea wind elements were used to systematically study the data obtained from contrast validation test in Zhoushan sea area of Zhejiang Province on Oct. 2000, to validate the accuracy of OSMAR2000 for wave and wind parameters, and to analyze the possible error caused when using OSMAR2000 to retrieve ocean parameters.

Comparison and error analysis of remotely measured waveheight by high frequency ground wave radar

High frequency ground wave radar （HFGWR） has unique advantage in the survey of dynamical factors, such as sea surface current, sea wave, and sea surface wind in marine conditions in coastal sea area. Compared to marine satellite remote sensing, it involves lower cost, has higher measuring accuracy and spatial resolution and sampling frequency. High frequency ground wave radar is a new land based remote sensing instrument with superior vision and greater application potentials. This paper reviews the development history and application status of high frequency wave radar, introduces its remote-sensing principle and method to inverse offshore fluid, and wave and wind field. Based on the author＇s ＂863 Project＂, this paper recounts comparison and verification of radar remote-sensing value, the physical calibration of radar-measured data and methods to control the quality of radar-sensing data. The authors discuss the precision of radar-sensing data＇s inversing on offshore fluid field and application of the assimilated data on assimilation.

Wave height measurement in the Taiwan Strait with a portable high frequency surface wave radar

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-or- der 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 ra- dar, 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.

Surface tidal currents in the open sea area to the east of the Zhoushan Islands measured with high frequency surface wave radar

Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of surface tidal currents in the open sea area to the east of the Zhoushan Islands of Zhejiang Province, China are studied. The following conclusions are drawn from the analysis： the tidal current pattern in the open sea area to the east of Zhoushan Islands is primarily regular semidiurnal, which is significantly affected by the shallow water constituents. The directions of the major axes of tidal current ellipses of M2 lie approx- imately in the NW-SE direction. With the increasing of distance away from the coast, the directions of the tidal current ellipses gradually shift toward the E-W direction. The tidal currents are mainly reversing cur- rents. The spatial distribution of probable maximum current velocities decreases gradually from northeast to southwest which is basically in accordance with the spatial distribution of measured maximum current velocities. The residual currents near the coast are larger than those far away from the coast. The directions of the residual currents are basically north by east, and the angle to the due north increases gradually with the increasing distance away from the coast. The topography shows a certain impact on the spatial distri- bution of shallow water constituents, the rotation of tidal currents, the probable maximum currents and the residual currents.

The Study of Single Station Inverting the Sea Surface Current by HF Ground Wave Radar Based on Adjoint Assimilation Technology

This paper introduces the assimilation technology in an ocean dynamics model and discusses the feasibility of inverting the sea surface current in the detection zone by assimilating the sea current radial velocity detected by single station HF ground wave radar in ocean dynamics model. Based on the adjoint assimilation and POM model, the paper successfully inverts the sea surface current through single station HF ground wave radar in the Zhoushan sea area. The single station HF radar inversion results are also compared with the bistatic HF radar composite results and the fixed point measured results by Annderaa current meter. The error analysis shows that acquisition of flow velocity and flow direction data from the single station HF radar based on adjoint assimilation and POM model is viable and the data obtained have a high correlation and consistency with the flow field observed by HF radar.

Wave height estimation using the singular peaks in the sea echoes of high frequency radar

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 and ±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.

Application of ESPRIT in Broad Beam HF Ground Wave Radar Sea Surface Current Mapping

HF surface wave radar system OSMAR2000 is a broad-beam sea-state detecting radar. ESPRIT (Estimation of Signal Parameters via Rotational Invariance Technique) algorithm is proposed to apply in DOA (direction of arrival) determination of sea echoes. The algorithm of ESPRIT is briefly introduced first. Then discussions are made on the technique for application in the OSMAR2000 framework. Numerical simulation results are presented to demonstrate the feasibility of radial current mapping based on this method. The algorithm manifests significant performance and computational advantages compared with that of MUSIC. Data acquired by OSMAR2000 are processed to give radial current map and the synthesized vector currents are compared with the in-situ measurement with traditional means. The results show the validity of ESPRIT application in DOA determination for broad-beam radar. Key words HF ground wave radar - sea surface current - ESPRIT - MUSIC CLC number TN 911.72 - TN 958.95 Foundation item: Supported by the National Natural Science Foundation of China (60201003) and the National High Technology Development 863 Program of China (863-818-01-02)Biography: Liu Dan-hong (1976-), female, Master candidate, research direction: radar signal processing.

Vessel fusion tracking with a dual-frequency high-frequency surface wave radar and calibrated by an automatic identification system

High-frequency surface wave radar（HFSWR） and automatic identification system（AIS） are the two most important sensors used for vessel tracking.The HFSWR can be applied to tracking all vessels in a detection area,while the AIS is usually used to verify the information of cooperative vessels.Because of interference from sea clutter,employing single-frequency HFSWR for vessel tracking may obscure vessels located in the blind zones of Bragg peaks.Analyzing changes in the detection frequencies constitutes an effective method for addressing this deficiency.A solution consisting of vessel fusion tracking is proposed using dual-frequency HFSWR data calibrated by the AIS.Since different systematic biases exist between HFSWR frequency measurements and AIS measurements,AIS information is used to estimate and correct the HFSWR systematic biases at each frequency.First,AIS point measurements for cooperative vessels are associated with the HFSWR measurements using a JVC assignment algorithm.From the association results of the cooperative vessels,the systematic biases in the dualfrequency HFSWR data are estimated and corrected.Then,based on the corrected dual-frequency HFSWR data,the vessels are tracked using a dual-frequency fusion joint probabilistic data association（JPDA）-unscented Kalman filter（UKF） algorithm.Experimental results using real-life detection data show that the proposed method is efficient at tracking vessels in real time and can improve the tracking capability and accuracy compared with tracking processes involving single-frequency data.

Estimation of detection threshold in multiple ship target situations with HF ground wave radar

A credible method of calculating the detection threshold is presented for the multiple target situations, which appear frequently in the lower Doppler velocity region during the surveillance of sea with HF ground wave radar. This method defines a whole-peak-outlier elimination （WPOE） criterion, which is based on in-peak-samples correlation of each target echo spectra, to trim off the target signals and abnormal disturbances with great amplitude from the complex spectra. Therefore, cleaned background noise samples are obtained to improve the accuracy and reliability of noise level estimation. When the background noise is nonhomogeneous, the detection samples are limited and often occupied heavily with outliers. In this case, the problem that the detection threshold is overvalued can be solved. In applications on experimental data, it is verified that this method can reduce the miss alarm rate of signal detection effectively in multiple target situations as well as make the adaptability of the detector better.

Estimation of the Direction of Arrival Using Virtual Matrix Method for HF Ground Wave Radar

According to the characteristic of the echo of highfrequency ground wave radar（HF GWR）, which is one-dimensional narrow band signal, a virtual direction of arrival（DOA） matrix is constructed at first, then the DOA of target evaluation is achieved by the method of resolving equations for two-dimensional DOA matrix. And this method bases on the redundancy information of a linear two-row array of antennae. Both the simulation process and the treatment results of measured data （in the case of low SNR echoes and short data series） are given at the end of this paper. By comparing with GPS data of the targets, the validity and practical applicability of the method in this paper is verified.

基于多帧聚类的紧凑型HFSWR虚假点迹识别方法

紧凑型高频地波雷达发射功率低,目标检测时信噪比低、虚警率高,会产生大量虚假点迹,影响后续目标跟踪性能。为了滤除虚假点迹,利用目标的运动特性,提出了一种多帧聚类与极限学习机分类两级级联的虚假点迹识别方法。首先,利用基于最优邻域尺寸的多帧聚类方法,将连续多帧中与待识别点迹属于同一潜在目标的点迹聚类成簇。然后,计算簇内待识别点迹与其相邻帧内点迹的距离-多普勒速度的差分值,以其为特征利用极限学习机辨识虚假点迹。实验结果表明,所提方法能够准确将属于同一目标的点迹聚类,虚假点迹识别率达到95%。

基于改进DeeplabV 3+的HFSWR电离层杂波及海杂波自动识别

针对高频地波雷达(HFSWR)回波谱中背景噪声复杂、杂波占比较小且电离层杂波形态位置各异,难以自动识别的问题,以DeeplabV3+深度学习算法为基础架构并加以改进,提出一种HFSWR电离层杂波及海杂波自动识别方法。选用轻量级MobileNetV2作为主干特征网络,加入通道注意力机制模块SENet,实现对杂波标签的侧重学习,优化训练集中各类标签的损失权重;采用模型预训练迁移法对网络进行预训练,解决样本空间过小的问题。实测数据集上的实验结果表明,本方法可以实现HFSWR电离层杂波及海杂波的自动识别。相比原DeeplabV3+算法,杂波识别结果更为准确和精细,海杂波识别结果的平均交并比(mIoU)和准确率(ACC)分别提升2.9%和5.1%;电离层杂波识别结果的mIoU和ACC分别提升3.0%和4.9%。

Lg-Q model and its implication on high-frequency ground motion for earthquakes in the Sichuan and Yunnan region

Low-rise buildings are susceptible to high-frequency ground motion.The high-frequency ground motions at regional distances are mainly controlled by crustal Lg waves whose amplitudes are typically much larger than those of body waves.In this study,we develop a Lg-wave Q model for the Sichuan and Yunnan region in the frequency band of 0.3–2.0 Hz using regional seismic records of 1166 earthquakes recorded at 152 stations.Comparison between the observed pattern of ground motion from real earthquake and model prediction demonstrates the robustness and effectiveness of our Lg-Q model.Then,assuming that the Lg-wave Q structure is the main factor affecting the propagation of the high-frequency ground motions,we calculate the spatial distributions of high-frequency ground motions from scenario earthquakes at different locations in the region using the average Lg-wave attenuation model over the frequency band of 0.3–2.0 Hz.We also use the Lg-Q model to estimate the distribution of cumulative energy of high-frequency ground motions based on the historical seismicity of the Sichuan and Yunnan region.Results show that the Lg-Q model can be used effectively in estimating the spatial distribution of high-frequency seismic energies and thus can contribute to the assessment of seismic hazard to low-rise buildings.

HFSWR海洋-电离层一体化探测实验与数据分析

高频地波雷达(High-frequency Surface Wave Radar,HFSWR)凭借其全天时、全天候和超视距探测等方面的能力,在海洋遥感与电离层探测应用方面均取得了阶段性进展,然而当前在海洋-电离层回波联合方面的研究还十分有限。本文基于哈尔滨工业大学(威海)HFSWR一体化探测系统,对台风“梅花”过境渤海湾期间的海洋回波与电离层回波进行了数据分析。首先对HFSWR一体化探测系统的整体构成进行了介绍,之后基于Bragg原理对海洋回波进行了海洋径向流速分析,并采用经验模态分解以及HHT变换方法对电离层回波进行能量谱分析。实验结果表明,在台风“梅花”过境期间,海洋回波与电离层回波均出现了明显的特征变化,两者之间存在一定的联动机制。本文提出了进一步研究海洋与电离层之间动力学关系的需要,并强调了HFSWR一体化探测系统的独特体制在海洋-电离层联合研究方面的优势。

Signal decomposition of HF radar maneuvering targets by using S^2-method with clutter rejection

Multiple maneuvedng targets signal processing in high frequency radar is challenging due to the following difficulties： the interference between signals is severe because of significant spread of the target Doppler spectrum, the low signal to clutter ratio （SCR） environment degrades the performance of signal process- ing algorithms. This paper addresses this challenging problem by using an S2-method and an adaptive clutter rejection scheme. The proposed S2-method improves the S-method by eliminating inter- ference between signals, and thus it enables multi-target signals to be reconstructed individually. The proposed adaptive clutter rejec- tion scheme is based on an adaptive notch filter, which is designed according to the envelop of the clutter spectrum. Experiments with simulated targets added into radar sea clutter echo and real air target data illustrate the effectiveness of the proposed method.

Theory and Analysis for First-Order Interaction Between HF Radio Waves and Ocean Waves

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道路地下空洞探地雷达波场和时频特性

根据城市道路地下介质的分布特征和电性参数设计模型,采用时域有限差分法和广义S变换,对道路地下存在的充气空洞、充水空洞、回填不密实、埋藏金属物状态进行探地雷达正演模拟和时频特征提取。结果表明,地下空洞顶界面的反射波同相轴均呈弧形反射形态,但充气空洞的反射波能量强于充水空洞;地下空洞发育区域的中心频率集中在某个低频区间,其余频率成分分布较均匀;埋藏金属物区域出现两簇高幅值能量团,频率分布较分散;回填不密实区域频率未能显示出较明显的规律。最后,通过工程实测验证了数值模拟的可靠性。

GPR信号去噪的变分模态分解

为了进一步提高探地雷达(ground penetrating radar,GPR)数据的信噪比,压制由随机扰动引起的随机绕射能量,将二维变分模态分解(two-dimensional variational mode decomposition,2D-VMD)引入二维GPR数据的噪声压制处理中。首先,对GPR数据进行2D-VMD处理,并分析各阶本征模态函数(intrinsic mode function,IMF)分量及其对应的频率-波数域谱来确定雷达剖面中的各回波类型。然后,计算IMF分量与原始数据的互相关系数来确定信号模态和噪声模态,并对信号模态进行重构得到降噪后的数据。理论数据和实测数据测试表明,相比于传统的1D-VMD法,2D-VMD滤波后的含噪正演记录峰值信噪比由6.44 dB增加到7.72 dB;经2D-VMD降噪处理后的雷达剖面在保留有效信号的基础上,可以有效压制随机扰动带来的噪声,并且得到的雷达剖面同相轴连续性更好。

基于改进SFLA-Elman神经网络的电离层杂波抑制方法

针对高频地波雷达目标检测中电离层杂波的干扰问题,提出了一种基于改进混合蛙跳算法优化Elman神经网络预测抑制电离层杂波的策略。为解决混合蛙跳算法初始种群分布不均匀、收敛精度低、易陷于局部极值等问题,引入Cubic混沌映射、莱维飞行策略、非线性平衡因子和复制操作,增强种群多样性,提高算法搜索能力。利用改进后的算法和其他算法分别优化Elman神经网络预测抑制模型,结果表明,改进后的算法无论是在收敛精度和稳定性上,还是在临近距离单元电离层杂波的预测抑制上,都取得了显著的提升。在基本保留目标信号的基础上,平均信杂比较原始回波提升18.52 dB,较原始混合蛙跳算法提升1.08 dB,对于电离层杂波的抑制具有较高应用价值。