IEE Proceedings - Radar, Sonar and Navigation
Volume 148, Issue 2, April 2001
Volumes & issues:
Volume 148, Issue 2
April 2001
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- Author(s): D.T. Gjessing ; R. Hansen ; J. Saebboe
- Source: IEE Proceedings - Radar, Sonar and Navigation, Volume 148, Issue 2, page: 49&:55 –49&:55
- DOI: 10.1049/ip-rsn:20010095
- Type: Article
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49&:55
The authors present a bistatic radio–acoustic system where a Bragg grid produced by a spherical pressure wave enhances the forward scattering capability by some 40 dB when matched to the EM phase front. The system is used to measure 3-D wind, turbulence and vortex parameters as wind phenomena alter the scattering characteristics of the acoustic Bragg grid. The criterion for Bragg scattering is only valid over a limited height interval in this system. This confines the scattering volume to the limits of the radio beam and the acoustic beam in the horizontal direction and the Bragg-criteria limitations in the vertical direction. This scattering volume can be shifted vertically by tuning the acoustic frequency to give spatial resolution. Illuminating the acoustic Bragg grid with a CW EM signal gives a continuously received signal from a small scattering volume at a given height. It is possible to continuously measure the real-time cross-path wind component and at the same time perform coherent integration over longer time intervals in investigating turbulence phenomena. Experimental verification supports the theoretical models and underlines the system's capacity to measure wind phenomena, vortex structures and turbulence parameters. - Author(s): F. Berizzi and E. Dalle Mese
- Source: IEE Proceedings - Radar, Sonar and Navigation, Volume 148, Issue 2, p. 56 –66
- DOI: 10.1049/ip-rsn:20010299
- Type: Article
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p.
56
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(11)
A new model of the sea-wave directional spectrum based on fractals is proposed. An innovative aspect of the work is the theoretical approach used to get the `fractal sea spectrum'. The common spectrum models are described by empirical expressions derived from fitting experimental data. Starting from a definition of a fractal model of the sea surface, the spatial autocorrelation function is calculated and the directional sea spectrum derived by taking its two-dimensional Fourier transform. The fractal spectrum explicitly accounts for the fractality of the sea. The spectrum theoretically explains why its slope in the equilibrium range depends on the fractal dimension D of the sea surface and can be expressed by the relationship 2D−7, as usually claimed from experimental data. The spectrum is validated by comparing it to the common spectra of Pierson–Moskowitz and JONSWAP and to real data of the Mediterranean sea. New research directions offered by this spectrum model in SAR remote sensing are addressed. - Author(s): J. Xie ; Y. Yuan ; Y. Liu
- Source: IEE Proceedings - Radar, Sonar and Navigation, Volume 148, Issue 2, p. 67 –71
- DOI: 10.1049/ip-rsn:20010135
- Type: Article
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67
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The spreading of the dominant first order Bragg lines in shipborne HFSWR (high-frequency surface wave radar) severely obscures targets with Doppler frequencies within the spreading domain. STAP (space–time adaptive processing) is one of the effective methods for solving the problem. The experimental one-dimensional spreading spectrum and two dimensional space–time spectrum of sea clutter in shipborne HFSWR are given. The eigenvalue distribution of the space–time covariance matrix is also obtained. All experimental results show good agreement with the spreading model of sea clutter and theoretical analysis of the eigenspectrum for a random process, which is of advantage for sea clutter suppression and target detection in shipborne HFSWR with STAP. - Author(s): D. Walker
- Source: IEE Proceedings - Radar, Sonar and Navigation, Volume 148, Issue 2, p. 73 –80
- DOI: 10.1049/ip-rsn:20010182
- Type: Article
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73
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Data from a cliff top radar experiment conducted off the south coast of England are examined in order to investigate the applicability of a three-component model for radar Doppler spectra, developed using laboratory wavetank data, to coastal water sea clutter. This is achieved by a detailed analysis of the prominent features in the cliff top radar data in terms of polarisation and Doppler characteristics, and decorrelation times. This analysis confirms the presence of the same Bragg and non-Bragg scattering mechanisms as observed in the laboratory wave tank. A dependence of each of the scattering mechanisms on wind direction can also be inferred, showing that Bragg resonant scattering from capillary waves and non-Bragg scattering from highly disturbed white water after a wave has broken are present in both the up and down wind cases, while the highly polarised HH `sea spikes' appear only when the radar is looking into the wind. It is shown that the three-component Bragg–whitecap–spike model for Doppler spectra is able to describe both the up and down wind cases well, and that the RMS tilt angle of the underlying gravity waves can be extracted from the Bragg scattering polarisation ratio via the composite surface scattering model. - Author(s): A.S. Paine
- Source: IEE Proceedings - Radar, Sonar and Navigation, Volume 148, Issue 2, p. 81 –88
- DOI: 10.1049/ip-rsn:20010183
- Type: Article
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p.
81
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For large phased array radar, digitisation and adaptive beamforming are usually performed at the subarray level. The number of subarrays is usually much smaller than the number of array elements thus reducing the number of available adaptive degrees of freedom (DOF). For an element digitised array radar (EDAR), a subarray technique can also be employed to reduce the number of adaptive channels in order to reduce the adaptive processing load. However, EDAR allows greater flexibility in the choice of adaptive channels from the array elements, thus allowing alternative DOF reduction techniques to be investigated. An adaptive technique using a convolution approach, namely `range-dependent gain adaptation using domain factorisation' (RDGA-DF), has been shown to give significant advantages over subarray level adaptive beamforming when cancelling strong sidelobe clutter in the airborne environment (Rees and Skidmore, 1998; Mather et al., 1999). A new implementation of the RDGA-DF algorithm is developed to perform adaptive processing on a domain factorised array. This algorithm, called the `full aperture convolution technique' (FACT), is derived directly from the optimal Wiener filter solution. The performance advantages of FACT over RDGA-DF are demonstrated by simulation. - Author(s): X.L. Qiao and M. Jin
- Source: IEE Proceedings - Radar, Sonar and Navigation, Volume 148, Issue 2, p. 89 –93
- DOI: 10.1049/ip-rsn:20010112
- Type: Article
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p.
89
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(5)
A new method of single sample polarisation filtering is proposed. The algorithm is fast and suitable for the polarisation processing of stationary or nonstationary polarised disturbed signals with one or more independent sources of disturbance. A ground wave polarimetric radar with the ability of radio disturbance suppression is then introduced. Some numerical results demonstrate the effectiveness of the single sample polarisation filtering method for ground wave polarimetric radar. - Author(s): F. Pérez-Martı́nez ; M. Burgos-Garcı́a ; A. Asensio-López
- Source: IEE Proceedings - Radar, Sonar and Navigation, Volume 148, Issue 2, p. 95 –100
- DOI: 10.1049/ip-rsn:20010136
- Type: Article
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p.
95
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The effect of group delay variations over the operation bandwidth of CW-LFM radars is investigated. Although present systems have no special problems with phase distortion, it is shown that for the next generation of low probability of interception radars this is a very important handicap. Main parameters relevant for the performance of the system are identified and some design techniques are proposed.
Characterisation of wind field with high resolution in time and space by the use of electromagnetic and acoustic waves
Sea-wave fractal spectrum for SAR remote sensing
Experimental analysis of sea clutter in shipborne HFSWR
Doppler modelling of radar sea clutter
Optimal adaptive processing for domain factorised element-digitised array radar
Radio disturbance suppression for HF radar
Group delay effects on the performance of wideband CW-LFM radars
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