By Topic

Radar, Sonar and Navigation, IEE Proceedings -

Issue 6 • Date Dec 1995

Filter Results

Displaying Results 1 - 7 of 7
  • Adaptive eigen-subspace algorithms for tracking suddenly disappearing sources

    Publication Year: 1995 , Page(s): 277 - 280
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    Adaptive eigen-subspace algorithms have advantages in tracking nonstationary signal parameters, for example, the directions of arrival in array signal processing. Most adaptive eigenstructure methods can track all moving and suddenly appearing sources. However, an interesting disadvantage of these algorithms is that they fail to track suddenly disappearing sources. As a result of this failure, false peaks will occur in the angular spectrum at the directions where the sources disappear. The authors show this inherent problem of adaptive eigen-subspace algorithms by theoretical derivations and simulation examples View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • New strategy to locate buried objects in highly lossy ground

    Publication Year: 1995 , Page(s): 306 - 312
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1012 KB)  

    An electromagnetic scale model, with well defined and variable electrical parameters, has been constructed, to investigate experimentally the optimum ground-probing radar strategies for use in extremely lossy conditions. A new geometry is proposed that reduces the dynamic-range requirements of a ground-probing radar, allows the permittivity of the medium to be estimated, and provides a clear time window for close targets to be detected. An image-retrieval algorithm is described for image reconstruction View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High order nonlinearities in HF radar backscatter from the ocean surface

    Publication Year: 1995 , Page(s): 293 - 300
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    HF radar measurements of ocean waves make use of a second-order theory for the hydrodynamic and electromagnetic processes that generate the received signal. The author presents evidence that the second order theory is not sufficient to explain the power spectrum of the received signal in all cases. This is not a new result; radars have been developed in both Britain and the USA that allow a reduction in radio frequency for operation in high sea-states. However, the data in the present paper were obtained at frequencies in the lower half of the HF band, and still show evidence of a significant departure from second order. The effect on ocean wave measurement appears to be small. The results reveal a directional dependence of this effect which may be compensating for the higher-order nonlinearities in the inversion of dual radar spectra. The use of the departure from second order theory to provide a crude significant waveheight estimate is suggested View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Detection of spread-spectrum signals using the time-domain filtered cross spectral density

    Publication Year: 1995 , Page(s): 286 - 292
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    The authors present a technique for the detection of spread-spectrum signals, of arbitrary form, even when the signal power spectral density (PSD) is well below the surveillance receiver noise spectral density, using a pair of antennas with broadband (1 GHz or more) receivers. Cross correlating the outputs of two receivers, spatially separated by a distance of the order of one metre or more, produces a cross-correlation function (CCF), in which the noise components are spread uniformly over the whole width, while the signal component, the narrow autocorrelation function (ACF) of the spread-spectrum signal, is concentrated in the centre. A simple time-domain filter can select this narrow centre portion of the CCF, rejecting the remainder which contains only noise. Taking the Fourier transform of this windowed CCF produces the `time-domain filtered cross spectral density' (TDFCSD), in which the signal to noise ratio is independent of receiver bandwidth. Spread-spectrum signals can then be both detected and characterised, in an extremely sensitive broadband system, by threshold detection in this TDFCSD. An analysis of the performance of this dual-receiver system is presented. A computer simulation illustrates the signal processing process involved, and shows excellent agreement with the analysis. A time-integrating acousto-optic correlator may be used to perform the cross correlation and time domain filtering of wideband signals in real time. Final processing of the much reduced data set to obtain the TDFCSD can be carried out digitally View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Image registration in interferometric SAR processing

    Publication Year: 1995 , Page(s): 313 - 320
    Cited by:  Papers (23)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1404 KB)  

    In interferometric synthetic aperture radar (IFSAR) applications image registration is needed to extract the correct phase difference between the two received signals. The authors present a new image registration procedure implemented at the raw data processing stage; the two complex SAR images are generated with respect to a common reference output system. The registration task is achieved via scaling and shifting compensation that can be efficiently and easily included in a standard SAR processing code. Examples on real as well as on simulated data validate the procedure. An algorithm to estimate the correct processing parameters, whenever the orbital information is inaccurate, is also presented and is based on the relation between spectral shift and linear stretch of the two images View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Frequency dependence of backscattered signals from forest components

    Publication Year: 1995 , Page(s): 301 - 305
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1480 KB)  

    The frequency dependence of statistics of radar signals scattered from forest are investigated through a simulation study based on a radiative-transfer theory. A forest canopy is modelled as a volume of needle-shaped or disc-shaped leaves and finite-length, cylindrical branches. It is expected that at radar frequencies above the X-band, scattering away from normal incidence is largely dominated by leaves, while a mixture of leaves and branches is important to model a forest canopy at the C-band. Thus, simulations of both a volume of leaves and a mixture of leaves and branches are of interest. It is assumed that all leaves and branches are randomly oriented. It is found that for leaves that are small compared with the incident wavelength, signal amplitude is Rayleigh distributed. Generally, this means the length of a needle-shaped leaf can be as long as kh (wavenumber×length) equal to 2, because its volume is small. However, for a disc-shaped leaf ka (wavenumber×radius) should be no more than 0.5 because its volume is much larger. When the leaves are comparable in size to the incident wavelength, signal amplitude assumes a gamma distribution. The signal amplitude distribution for a mixture of branches and leaves is also well represented by a gamma distribution because, here, the scatterer volume is also large in dimension relative to the incident wavelength View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theoretical performance of a multisensor track-to-track correlation technique

    Publication Year: 1995 , Page(s): 281 - 285
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    A multisensor track-to-track correlation technique, originally proposed by Singer and Kanyuck (1971) is analysed. It is shown that the probability of correlating two tracks is a function of two dimensionless scalar parameters, T and W. T is a threshold which guarantees a selected successful correlation probability when no biases exist between the two tracks state estimates. W is a normalised parameter which indicates the magnitude of the biases in position and rates which may exist between tracks. Results are presented for the probability of track-to-track correlation for various T and W values. The analysis is extended to quantify the probability of false association when two tracks from sensor B correlate with one track from sensor A and the conflict is resolved incorrectly. The false association probability is shown to be a function of three dimensionless parameters T, W and Δ where T is the same threshold parameter as previously, W is a measure of the biases between the incorrectly paired tracks and Δ is a relative measure of uncertainty between the two track pairings. Numerical results for the false association probability are presented for various T, W and Δ values. The results will be of interest to scientists and engineers involved in multisensor system design View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IEE Proceedings Radar, Sonar and Navigation covers the theory and practice of systems involving the processing of signals for radar, radio location, radio navigation and surveillance purposes.

Full Aims & Scope