Wu Xiongbin

Broad Beam HFSWR Array Calibration Using Sea Echoes

A novel technique to calibrate nonlinear array of HFSWR (HF surface wave radar) by exploiting single-DOA (direction of arrival) sea echoes only is presented. It works online to supply precise channel unmatching factors in real time without interrupting regular radar operating. The technique exhibits excellent robusticity and practicability when applied to the OSMAR (ocean state monitoring and analyzing radar) HFSWR system developed by Wuhan University

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.

Detection of the number of signals in super-resolution ocean surface current algorithm for OSMAR2000

Super-resolution ocean surface current algorithm based on MUltiple SIgnal Classification (MUSIC) is used for current mapping of Wuhan Universitys ocean state measuring and analyzing radar (OSMAR2000), in which MUSIC is applied to estimate the bearings of the first-order sea echo signals. The premise of MUSIC processing is that the number of signals is known in advance. In fact, the number of signals is unknown, and needs to be estimated from received data. In the case of discrete targets, the problem can be perfectly solved using information theoretic criteria such as the Akaike Information Criterion (AIC) or the Minimum Description Length (MDL) criterion. However, these criteria are proved unsuccessful for sea echo signals both in simulation and in actual application, since sea surface is essentially a continuum. Therefore, an ad hoc method of detection of number of signals, a bit different from the existent methods, is developed for the current algorithm of OSMAR2000. The underlying idea is to determine the number of signals based on the variance of MUSIC spectra structure under different candidate number of signals.

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.

The relationship between mutual coefficient errors and the amplitude and phase errors of channels

In general, an accurate mutual coupling correlation is necessary for an array antenna to reach ideal sideiobe level. If the mutual coefficient matrix of an array antenna is perfectly known, one can completely compensate the effect of mutual coupling and realize the desired sidelobe level in theory. However, the mutual coefficient matrix obtained wherever by calculation on by measurement has a limited precision. In this paper, the requirements on the precision of matrix coefficient for compensation in low sidelobe array antenna are discussed. The relationship between mutual coefficient errors and the amplitude and phase errors of channels is derived.

Research on spherical antenna array imaging by simulation

This paper mainly studies on the spherical array imaging with spatial matched filtering. The azimuth resolution of circular trace scanning synthetic aperture radar is calculated. The factors affecting the azimuth resolution of the spherical array imaging are discussed, and a method of amplitude weighting is proposed to restrain the side lobe. Finally, the imaging effect of two kinds of array elements distribution is compared.

A study on hybrid networking system for distributed HF over-the-horizon radars

The hybrid networking system for distributed HF over-the-horizon radars is presented and analyzed in this paper, which includes two modes: the hybrid sky-surface wave system consisting of a sky wave transmitting path and a surface wave receiving path, and the surface wave system consisting of a surface transmitting path and a surface wave receiving path. The system will be used in remote monitoring wide areas ocean dynamics parameters. Compared with the single mode radar system, this system has advantages of better detection performance at the far ranges and stronger anti-interference ability. The configuration of the hybrid networking system, the key problems and corresponding techniques are introduced. Preliminary results from field experiments show the technical feasibility and the good detection performance of the new radar networking system.

The study on the numerical simulation and inversion of shallow sea depth based on microwave radar

In this paper, a detection method of shallow sea depth utilizing the microwave radar is proposed. The method is based on the sea clutter imaging mechanism of microwave radar, and combined with dispersion equation of the liner wave theorem and least square method (LSM), consequently get the inversion results of water depth in the detected region. The wave monitoring system OSMAR-X exploited by Ocean State Laboratory, Wuhan University, based on a microwave radar has proven to be a powerful tool to monitor ocean waves in time and space. By analysing a sequence of radar images captured by OSMAR-X, numerical simulation and inversion of shallow sea depth are carried out here, since JONSWAP model can give description of stormy waves in different growth phase, its suitable for simulation. Besides, some results from measured data detected by OSMAR-X x-band radar located at Longhai of Fujian Province, China validates this method. The tendency of the average water depths inferred from the radar images is in good agreement with the tide level detected by Xiamen tide station. These promising results suggest the possibility of using OSMAR-X to monitor operationally morphodynamics in coastal zones. This method can be applied to both shore-based microwave radar and shipborne microwave radar.

Ionospheric clutter analysis and suppression in a distributed MIMO-HFSWR system

In distributed MIMO (multiple-input-multiple-output)-HFSWR (high frequency surface wave radar), multiple detection modes are introduced to enrich the detection information, however making ionospheric clutter more complicated. In this paper, a distributed MIMO-HFSWR system involving three monostatic radars is introduced. Sea echo and ionospheric clutters from different paths are received simultaneously by MIMO system. Characteristic of ionospheric clutter in range domain and Doppler domain are analyzed with measured data. It is discovered that the correlation of ionospheric clutters from different paths is higher than of sea echoes. Based on this, a novel method for clutter suppression is proposed via adaptive filter using clutters from different paths as secondary data. Experimental results show that the analysis and processing method are feasible and effective.

A study on skywave-surfacewave hybrid networking technique for HF oceanography radar

HF over the horizon radar can be divided into sky wave radar and the surface wave radar according to the radio propagation mode. As a new mode, HF hybrid sky-surface wave radar is composed of the ionosphere reflection propagation mode and the surface wave receiving mode. The technique of HF sky wave and surface wave hybrid networking system for HF oceanography radar is presented and analyzed in this paper, which includes two modes: the hybrid sky-surface wave system consisting of a sky wave transmit path and a surface wave receive path, and the surface wave system consisting of a surface transmit path and a surface wave receive path. Based on this hybrid networking technique, the system combines the merits of surface wave HF radar and sky-surface wave radar, which will improve the ability of target detection and enlarge the detection range. Compared with the single mode radar system, this system has advantages of better detection performance at the far ranges and stronger anti-interference ability. The structure of the hybrid networking system is given. Besides receiving the sea echo from the surface wave radar, HF receiving array on the shore also receives the sea echo from the sky wave transmitting station that is reflected from the ionosphere. The sea echo signals from different transmitting stations is obtained and separated by frequency offset or timing delay. Finally, the experimental system and experimental data analysis are provided. The experimental results under different scenarios including hybrid sky-surface propagation mode and hybrid networking mode are presented. Preliminary results from field experiments show the technical feasibility and the good detection performance of the new radar networking system.