High Frequency Ground Wave Radar Research Articles

MIMO Ground Wave Radar Radio Frequency Monitoring

High Frequency (HF) ground wave radar is widely used in maritime target detection and marine environment observation. Its performance is often degraded by co-frequency interference of the HF band. It is necessary to detect the environmental radio frequency for a HF radar to select the proper operation frequency. In this paper, a radio frequency detecting module is designed and equipped on a double-frequency all-digital multi-input and multi-output (MIMO) HF radar. The operational frequency bands are scanned in the operation of the radar to help select an unoccupied frequency in the band. The application of this module reduced the influence of RF interference on the HF radar. The improvement in the signal quality is obvious.

High-Frequency Radar Cross Section of Ocean Surface for an FMICW Source

The frequency-modulated interrupted continuous waveform (FMICW) has been widely used in remotely sensing sea surface states by high-frequency ground wave radar (HFGWR). However, the radar cross section model of the sea surface for this waveform has not yet been presented. Therefore, the first- and second-order cross section models of the sea surface about this waveform are derived in this study. The derivation begins with the general electric field equations. Subsequently, the FMICW source is introduced as the radar transmitted signal to obtain the FMICW-incorporated backscattered electric field equations. These equations are used to calculate range spectra by Fourier transforming. Therefore, Fourier transformation of the range spectra calculated from successive sweep intervals gives the Doppler spectra or the power spectral densities. The radar cross section model is obtained by directly comparing the Doppler spectra with the standard radar range equation. Moreover, the derived first- and second-order radar cross section models for an FMICW source are simulated and compared with those for a frequency-modulated continuous waveform (FMCW) source. Results show that the cross section models for the FMICW and FMCW cases have different analytical expressions but almost the same numerical results.

Multi-Channel Data Acquisition Card under New Acquisition and Transmission Architecture of High Frequency Ground Wave Radar

It is known that the data acquisition and processing system plays an important role in radar target detection system. In order to meet the requirements of real-time processing and accurate transmission of echo signals in high-frequency ground-wave radar (HFGWR) systems, a new acquisition and transmission framework utilizing the designed acquisition card based on the PCIe (peripheral component interconnect express) has been designed and is presented in this paper. The Xilinx FPGA (Field-Programmable Gate Array) chip Kintex7-XC7K325T is adopted as a hardware carrier in acquisition card. The hardware’s composition, analog front-end circuit, the DMA (Direct Memory Access) transmission, FPGA structure, ADC (Analog-to-Digital Converter) chip, and performance test of this card are showed and discussed. Currently, the acquisition card has been accomplished and applied in the practical system of HFGWR.

Advanced Sea Surface Target Detection System for Shipborne VHF Radar in Log Periodic Dipole Array Antenna

While navigating in sea target detection is an important problem in modern era communication. In the ocean to detect moving targets and to analyze active variables such as wind, waves and current we can make use of Very High Frequency Ground Wave Radar (VHFGWR). In shipborne VHFGWR the brag spectra widened by Doppler Effect of the ship motion, due to this vessel echo easily merged.An orthogonal projection method to suppress the extended Brag spectra using a log periodic dipole array is proposed in this paper. The advanced technique majorly covers two stages: 1) by utilizing sea echo parameters calculate the approximation of sea clutter in spatial domain and 2) design multi frequency classification Doppler bins method to suppress the extended Brag spectra. After echo suppression, for target detection we can use different algorithms. Simulation result gives a proof that signal- to- clutter noise ratio (SCR) is developed and sea clutter got removed. This method gives very good target detection for shipborne VHF radar.

A New Multigrid 3D-VAR Optimization Method for Bottom Friction Using HF Radar Current Observation

This paper proposes a new method for data assimilation of the surface radial current observed by High Frequency ground wave radar and optimization of the bottom friction coefficient. In this method, the shallow water wave equation is introduced into the cost function of the multigrid three-dimensional variation data assimilation method as the weak constraint term, the surface current and the bottom friction coefficient are defined as the analytical variables, and the high spatiotemporal resolution surface radial flow observed by the high-frequency ground wave radar is used to optimize the surface current and bottom friction coefficient. This method can effectively consider the spatiotemporal correlation of radar data and extract multiscale information from surface radial flow data from long waves to short waves. Introducing the shallow water wave equation into the cost function as a weak constraint condition can adjust both the momentum and mass fields simultaneously to obtain more reasonable analysis information. The optimized bottom friction coefficient is introduced into the regional ocean numerical model to carry out numerical experiments. The test results show that the bottom friction coefficient obtained by this method can effectively improve the accuracy of the numerical simulation of sea surface height in the offshore area and reduce the simulation error.

Sea Clutter Suppression for Shipborne HF Radar Using Cross-Loop/Monopole Array

The shipborne high-frequency ground wave radar (HFGWR) provides a better condition for sea surface target detection than the shore-based one because of its maneuverability and flexibility. However, the first-order Bragg spectra of the shipborne HFGWR would be broadened by the Doppler shift of the ship motion, which makes the vessel echo easily submerged. Even though some methods have been applied to suppress the broadened Bragg spectra for target detection, most of them are hard to achieve good result in a small-aperture radar. An orthogonal projection method to suppress the broadened Bragg spectra using a cross-loop/monopole array is proposed in this letter. The proposed method mainly includes two steps: 1) estimate the space of sea clutter in a spatial domain according to the ocean echo characteristics and 2) design an adaptive filter of single or multiple Doppler bins on the estimated clutter space to suppress the first-order spectra. After suppression, we use the multiple signal classification algorithm to estimate the incident direction of targets. The experimental data validate that the sea clutter is well suppressed and the target signal-to-clutter ratio is increased by the algorithm.

Evaluation on surface current observing network of high frequency ground wave radars in the Gulf of Thailand

Due to the high cost of ocean observation system, the scientific design of observation network becomes much important. The current network of the high frequency radar system in the Gulf of Thailand has been studied using a three-dimensional coastal ocean model. At first, the observations from current radars have been assimilated into this coastal model and the forecast results have improved due to the data assimilation. But the results also show that further optimization of the observing network is necessary. And then, a series of experiments were carried out to assess the performance of the existing high frequency ground wave radar surface current observation system. The simulated surface current data in three regions were assimilated sequentially using an efficient ensemble Kalman filter data assimilation scheme. The experimental results showed that the coastal surface current observation system plays a positive role in improving the numerical simulation of the currents. Compared with the control experiment without assimilation, the simulation precision of surface and subsurface current had been improved after assimilated the surface currents observed at current networks. However, the improvement for three observing regions was quite different and current observing network in the Gulf of Thailand is not effective and a further optimization is required. Based on these evaluations, a manual scheme has been designed by discarding the redundant and inefficient locations and adding new stations where the performance after data assimilation is still low. For comparison, an objective scheme based on the idea of data assimilation has been obtained. Results show that all the two schemes of observing network perform better than the original network and optimal scheme-based data assimilation is much superior to the manual scheme that based on the evaluation of original observing network in the Gulf of Thailand. The distributions of the optimal network of radars could be a useful guidance for future design of observing system in this region.

Study on Pattern Distortion and DOA Estimation Performance of Crossed-Loop/Monopole Antenna in HF Radar

Crossed-loop (CL)/monopole antenna has been widely used in high-frequency ground-wave radar for ocean surface remote sensing owing to its compact size. The multiple signal classification (MUSIC) algorithm is commonly adapted to achieve a favorable angular resolution for this broad beam antenna. However, the direction of arrival (DOA) estimation is always troubled by the frequently occurring distortion of antenna pattern. Previous studies are mainly focused on the calibration by using the actual pattern or other assistant algorithms. In this paper, theoretical analysis is made to illustrate the reason for pattern distortion, which draws a conclusion that the distortion is essentially due to the different influence of environmental obstacles upon the electric field part and magnetic field part. This also implies that there is nearly no distortion between the two loops, which is validated by three different experiments. Based on this conclusion, the DOA estimation performance of the MUSIC algorithm is studied by creating a numerical relationship associating the estimation error with distortion level. Furthermore, a new method using ideal pattern is proposed to improve the estimation performance by removing the amplitude information of monopole and relying on the CL processing. Both simulation and experimental results are given to prove its validity.

Analysis of Ship RCS Detected by Multifrequency HFGWR

One of the important applications of high frequency-ground wave radar (HFGWR) is to detect offshore ships. A proper method should be used to obtain the ship radar cross section (RCS), which is a key parameter of the ship. This paper proposes a method based on an automatic information system (AIS). The relationship of the ship RCS versus bearing for different frequencies is analyzed by processing multifrequency HFGWR data. With this new method, bearing information is taken into consideration, which is not the case in traditional empirical formulas. The results provide prior knowledge for ship detection and tracking; therefore, the probability of detection is significantly improved.

Analysis of the Vector Current Velocity Detecting Precision of Bistatic High-frequency Ground Wave Radar System

Analysis of the Vector Current Velocity Detecting Precision of Bistatic High-frequency Ground Wave Radar System

Bi-Station Multi-Target Tracking Using Range and Doppler Measurements

The azimuthal measurements of the high frequency ground wave radar are poor in an actual environment, which can cause the plots highly decentralized and damage the formation of the over-the-horizon tracks. To solve the problem, a new radar system is proposed to triangulate target tracks using range and Doppler measurements only. On the basis of the analysis of the characteristics of the range-finding location, a multi-target tracking algorithm under non-clutter condition is given in this paper, which further improves the tracking algorithm of this system. Simulation results show the effectiveness of this method.

The Application of a Novel Complementary Signal to High-frequency Ground Wave Radar

The Application of a Novel Complementary Signal to High-frequency Ground Wave Radar

An Inversion Method for Extraction of Wind Speed From High-Frequency Ground-Wave Radar Oceanic Backscatter

A new approach to extracting sea surface wind speed from high-frequency radar Doppler spectra is presented. Based on certain appropriate approximations associated with the Doppler region close to the first-order (Bragg) peaks, the second-order radar cross section equation is differentiated. Once Doppler shifts due to ocean currents are removed from the data, an expression that relates the wind speed to the frequency position of the second-order peak is derived. The method is applied to simulated noisy data as well as to field data obtained from a Seasonde (a product of CODAR Oceans Sensors) in Breezy Point, NY. In the latter case, the retrieved wind speeds are then compared to ground truth data measured by an anemometer from a National Oceanic and Atmospheric Administration weather station located in the vicinity of the illuminated patch of ocean. Subject to certain constraints as detailed in the manuscript, the algorithm shows significant promise.

Low velocity target detection based on time-frequency image for high frequency ground wave radar

The Doppler spectral broadening resulted from non-stationary movement of target and radio-frequency interference will decrease the veracity of target detection by high frequency ground wave (HFGW) radar. By displaying the change of signal energy on two dimensional time-frequency images based on time-frequency analysis, a new mathematical morphology method to distinguish target from nonlinear time-frequency curves is presented. The analyzed results from the measured data verify that with this new method the target can be detected correctly from wide Doppler spectrum.

Estimation of the direction of arrival using virtual matrix method for HF ground wave radar

According to the characteristic of the echo of high-frequency 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.

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 off-shore fluid field and application of the assimilated data on assimilation.

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.

Measuring Surface Wind Direction by Monostatic HF Ground-Wave Radar at the Eastern China Sea

The extraction of full wind vectors from data obtained by single-site (monostatic) high-frequency ground-wave radar (HFGWR) is an ongoing challenge because of the inherent directional ambiguities. Here, a new algorithm for resolving the ambiguity of wind direction from monostatic data is presented. The true wind direction is determined by minimizing the sum of the difference among three wind directions derived from three different radar look angles. The wind directions estimated by applying the algorithm to data obtained from the OSMAR2000 HFGWR situated at the Eastern China Sea are compared with values obtained from ship-borne instrumentation. The mean difference between the ground-truthed values and those obtained from the radar data is approximately 20/spl deg/. The distance limit for wind direction sensing using the OSMAR2000 is about 200 km, which is the range for which signal-to-noise ratios typically exceed about 23 dB in the relevant first-order portions of the backscatter spectra.

HF radar wave and wind measurement over the Eastern China Sea

High-frequency (HF) radar can be employed to measure sea surface state parameters such as waveheight, wind field, and surface current velocity. This paper describes the application of the HF ground wave radar in remote sensing the surface conditions over the Eastern China Sea in October 2000. The radar, referred to as the OSMAR2000, was developed by Wuhan University. Preliminary wave spectra, waveheights, and wind fields estimated from the collected data are presented and compared with ship-recorded measurements where such are available. The range for wind direction sensing is up to 200 km. Wave information and wind speed can be provided up to a range of 120 km. The mean difference between radar- and ship-measured significant waveheight is 0.323 m; wind direction is measured within 20/spl deg/; and wind speed to within 0.6 m/s. With such agreement being fairly reasonable, the feasibility of the inversion algorithm and the ocean state real-time sensing capability of OSMAR2000 are demonstrated.

Target detection and tracking with HF radar using reciprocal SAR techniques

Sustained research and development at Memorial University of Newfoundland has led to an operational High Frequency Ground Wave Radar (HF-GWR) system for coastal surveillance. This radar system has demonstrated over-the-horizon detection of targets such as vessels, ice hazards and low-flying aircraft, and performed ocean parameter measurements over a large area. The industrial developers of offshore hydrocarbon reserves in ice infested regions have an urgent requirement for the long range detection and tracking of icebergs from their production platforms. However, due to space restrictions, a rig- or ship-based system can only accommodate a compact antenna array. The uniform trajectory and low velocity of icebergs is ideal for Reciprocal Synthetic Aperture Radar (RSAR) processing with long target dwell times. The proven ice detection capability of HF-GWR systems, coupled with the compact antennas suggested by the RSAR technique, can be used to develop a rig- or ship-based all-weather surveillance device for ice hazards. It is also anticipated that the results of this research will allow the use of shorter antenna arrays for many other applications. Preliminary results using real data from the operational HF-GWR system are presented.