Wu Shicai

Super-resolution ocean surface current algorithm based on MUSIC for OSMAR2000

Owing to the decametric wavelength, a large aperture antenna array is needed for high frequency (HF) ground radar to obtain high angular resolution with conventional beam forming (CBF); for the case of a compact antenna or small aperture array, spatial super-resolution algorithms are used to get satisfactory angular resolution. Wuhan Universitys ocean state measuring and analyzing radar (OSMAR2000) is expected to real-time extract ocean surface current, wave and surface wind information at medium-range and long-range. To obtain long-range (i.e. 200 km) current mapping, the radar frequency must be selected in the lower region of the HF band, e.g. 7.5 MHz. Digital beam forming (DBF) is applied with the 120 m-long phased array to determine the bearings of the sea echo with 15/spl deg/ resolution for wave and wind extraction. The angular resolution is, however, too coarse for current mapping, especially when the ocean current detection range is as far as 200 km. Consequently, a super-resolution ocean surface current algorithm based on multiple signal classification (MUSIC) is developed for OSMAR2000. The relative theory basis, processing procedure and preprocessing and postprocessing associated with the algorithm are given. The comparison of OSMAR2000 measurements with the measurements from a current meter and the Seasonde system shows the ocean surface current algorithm based on MUSIC for OSMAR2000 can meet the requirements of the project contract successfully.

A waveform generate unit suitable for software defined HFSWR

A new radio frequency waveform generate unit is presented for software-defined high frequency surface wave radar (HFSWR). Since HFSWR operates in congested band, to suppress interference and clutters, together obtain the optimal combined sequence of waveform parameters, the radar system should be designed based on software radio principle. In this paper we discuss a software defined HF radar system-OSMAR2003, and focus on design and implementation of waveform generate unit for it. The proposed waveform generation unit integrates a frequency synthesizer with low phase noise and high signal to noise rate and a re-configurable synchronization control unit. The design is started with examination of requirements of the waveform and then optimize architecture of the combination of the synthesizer technology to satisfy the system requirements. Followed is the FPGA (field programmable logic array) based synchro unit controlled by VXI-bus. The measurement shows that the transmitted signal can be synthesized quickly with phase noise less than -109 dBc/Hz at 1-kHz off carrier and spur suppression greater than 65 dBc, While the waveform parameters can be set by VXI-bus. The signal generate unit becomes an important part of the software defined HFSWR and field experiments provide the validity.

Some problems in general scheme for HF ground wave radar engineering

f in : Wuhan Daxue Xuebao (Ziran Kexue Ban) , 2001 ,47(5) : 5 1 3 ~ 5 1 8 ] S o m e P r o b l e m s in Genera l S c h e m e for HF G r o u n d Wave Radar E n g i n e e r i n g YANG Zi-jie, WU Shi-cai, HOU Jie-chang, WEN Bi-yang, SHI Zhen-hua (School of Electronic Information,Wuhan University, Wuhan 430072,Hubei,China) Abstract: Some important problems in the system design and development of the HF Ground Wave Radar ( G W R ) OSMAR2000 are discussesd, concerning 1) estimation of GWR detection capabil i t ies;2) frequency modulated interrupted continuous wave ( F M I C W ) and pseudo noise phase modulation; 3) means to oppress near-sea echos~ 4) broad-beam phased array antenna and digital beam forming (DBF) technique~ 5) echo signal processing and zero-frequency interfere restricting approaches; 6) forming mode of I /Q~ 7) elimination of distance overlap and Doppler frequency overlap. In the fieldwork in Chinese East Sea we found that by using 120 m long, 8 antenna in which one for transmitt ing and all 8 for receiving, OSMAR2000 can detect current more than 200 km away with 120 ~ augular coverage and angular resolutionin of 2 ~ to 5 ~ in the dayt ime, and wind and wave at the distance of 100 kin. Our next research will concentrate on antenna miniaturization and universal GWR hardware platform using software radio technique as well as improve inversion algori thm for wind and wave.

Scattering from Rough Surfaces Using the 'Shooting and Bouncing Rays' Technique

The “shooting and bouncing rays” (SBR) technique is used to analyze the electromagnetic scattering characters of ocean rough surfaces varying with time. Some numerical results are presented and compared with the method of moments, and some factors, such as the incident angle, polarization and frequency are investigated which influence on electromagnetic scattering characters of ocean rough surfaces.

The effect of phase noise on the remote sensing of ocean surface currents

This paper studied the phase noise effect on the range spectrum and Doppler spectrum measured by high frequency (HF) radar which was used for remote sensing of sea surface state parameters. The presence of phase noise in the master oscillator caused a widening of the range spectrum and clutter velocity spectrum, degrading the range and velocity resolution. In this paper, a practical phase noise model is presented, and based on it, the relationship between the phase noise power spectrum density (PSD) and cumulative phase noise is investigated. Then, the basic minimum requirements for the PSD are calculated to maintain radar performance. The results show that a commercial off the shelf oscillator can meet the phase noise requirements.

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.

Daytime interference nulling of OSMAR

In order to cancel the daytime interference of Ocean State Monitoring and Analyzing Radar, which appears in some consecutive days, we analyze the interference characteristic. Based on the characteristic the sidelobe cancellation technique and the orthogonal expansion method are proposed to cancel the interference. Both methods increase the sea-echo-to-interference ratio, but the latter achieves better effect in the far distance, which confirms the orthogonal expansion is the best method to remove the interference.

The design of frequency synthesizer for the ocean state measuring and analyzing radar

The design and realization of a synthesizer for high frequency radar, OSMAR2003 (ocean state measuring and analyzing radar), is proposed. To provide a 47.5 MHz local signal and 7 MHz transmitting signal, two kinds of frequency synthesizer architectures are presented, and their advantages and disadvantages are compared. The preferred synthesizer is based on an architecture supporting a flexible combination of direct synthesizer and DDS (direct digital synthesizer) techniques with a low frequency reference crystal oscillator. The benefit of this architecture is the generation of signals with low phase noise and low spurious level. The measured output spectrum and field experiments undertaken in Zhujiajian Island demonstrate successful frequency synthesis operation.

Synchro controller of radar on FPGA

This paper mainly represents the realization of synchro controller based on the programmable logic devices FPGA by request of HF ground wave radar synchro controller under the instance of making the best of the virtues of FPGA. This design introduces the data communication between PC and synchro controller byI2C Bus, which can carry the synchronous signals’ parameters to RAM of synchro controller, then according to the theory that the result of comparing counter value with signals’ parameters is the needed wave, we produce all waves HF ground wave radar needs, moreover all waves are produced time-sharing in order to save resources.

HF radar wind measurement over the Eastern China Sea

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 high frequency ground wave radar OSMAR2000 developed by Wuhan University in remote sensing the surface condition over the East China Sea in October 2000. The preliminary wind field estimated from the collected data is outlined and compared with the ship-recorded results. The range for wind direction sensing is up to 180 or 220 km, wind speed can be provided out to a range of 80 or 120 km. The mean difference of wind direction is 20/spl deg/ and wind speed is measured to within 0.6 m/s; the agreements are fairly good. The feasibility of the inversion algorithm and ocean state real-time sensing capability of OSMAR2000 are demonstrated.