As the undesired echo from a radar environment (clutter) is often not Rayleigh distributed, problems arise in specifying the clutter as a non-Gaussian random process and in computer-generating realisations of clutter for simulation purposes. The paper shows that modelling the clutter as a compound Gaussian or a spherically invariant random process allows a complete specification of the clutter suitable for use in radar design. It also lends itself readily to computer simulation procedures. Specific procedures for generating clutter realisations with assigned correlation properties and with K or Weibull amplitude distributions are suggested, and are validated by statistical tests. Then the issue of resolving between the Weibull and K distributions is considered, and empirical operative characteristics of the associated hypothesis test are computed.

Modelling and simulation of non-Rayleigh radar clutter

The paper deals with the problem of radar detection of a target echo embedded in Weibull clutter and white Gaussian noise (WGN). Relevant features of the paper, with respect to previous papers on the same subject, refer to the coherent nature of the Weibull process (that modelling the clutter) and of the processing chain. In more detail, the in-phase and quadrature components of the clutter echoes have been modelled to give a Weibull probability density function (PDF) of the amplitude and a uniform PDF of the phase. Any shape of the correlation function among consecutive clutter samples is also allowed in the model. The so called 'coherent Weibull clutter' (CWC) introduced in the paper represents a suitable generalisation of the conventional ?coherent Gaussian clutter? (CGC). The processing chain is also coherent, i.e. it operates on the in-phase and quadrature components of the signals. To derive a suitable processing scheme, we resort to the general theory of radar detection which applies to any type of PDF and autocorrelation function (ACF) of the target and clutter. Briefly, it is found that the processing scheme is based on two nonlinear estimators of the clutter samples in the two alternative hypotheses (i.e. H0 and H1 the fully fledged architecture being discussed in the paper. The detection processor turns out to be a suitable generalisation of that concerning the CGC case. A new family of processing schemes is derived in accordance with the statistical model assumed for the useful target. The following cases are covered: target known a priori, Swerling 0, 1 and 2 models, and partially fluctuating target. Attention is also paid to the interesting case of a target modelled as a coherent Weibull process. The detection of such a target against white Gaussian noise is worked out. The detection performance of the a

Theory of radar detection in coherent Weibull clutter

The detection of signals with unknown parameters in correlated K-distributed noise, using the generalised Neyman-Pearson strategy is considered. The a priori uncertainty on the signal is removed by performing a maximum likelihood estimate of the unknown parameters. The resulting receivers can be regarded as a generalisation of the conventional detector, but for a zero-memory nonlinearity depending on the amplitude probability density function of the noise as well as on the number of integrated pulses. It is shown that the performance for uncorrelated observations is unaffected by the specific signal pattern, but depends only on the signal-to-noise ratio; moreover, the effect of the clutter correlation on the performance can be accounted for simply by a detection gain. A performance assessment, carried out by computer simulation, shows that the proposed receivers significantly outperform conventional ones as the noise amplitude probability density function markedly deviates from the Rayleigh law. It also shows that the generalised Neyman-Pearson strategy is a suitable means of circumventing the uncertainty on wanted target echos since the operating characteristics of the receivers for the case of signals with unknown parameters closely follow those of the receiver for a completely known signal.

http://lops.perso.enseeiht.fr/papers/Conte_IEE_Proc_F_1991b.pdf

Radar detection of signals with unknown parameters in K-distributed clutter

The paper deals with the problem of radar detection of a target echo embedded in log-normal clutter and white Gaussian noise. Relevant features of this article, with respect to previous papers on the same subject, refer to the coherent model assumed for the clutter and the processing chain. In more detail, the in-phase and quadrature components of clutter have been modelled to give a log-normal amplitude distribution and a near uniform distribution of the phase. Any shape of the correlation among consecutive clutter samples is also allowed in the model. At the same time, the processing chain is also coherent, i.e. it operates on the two components of the signals. Two architectures have been considered for the processor. The first, used in current practice, is formed of a linear transversal filter (for the clutter attenuation and the target echo enhancement) cascaded with a quadratic envelope detector and a comparison with a suitable threshold. The second processor considered differs from the previous one in the filter for clutter cancellation. A nonlinear homomorphic filter has been conceived to obtain a better suppression of clutter. The detection performance of the two processing chains have been evaluated, by means of computer simulation, in a number of operational cases of intrest. The paper gives a first contribution to the problem of finding better models of disturbance and of deriving more efficient processing chains.

Coherent radar detection in log-normal clutter

Weibull-distributed ground clutter of cultivated land was measured using an L-band long-range air-route surveillance radar (ARSR) having a 3.0 ?s pulsewidth and a 1.23° beamwidth at very low grazing angles between 0.21° and 0.32°. It is shown that the shape parameter of the Weibull distribution varied from c = 1.507 to c = 2.0, corresponding to the Rayleigh distribution.

Weibull-Distributed Ground Clutter

Weather clutter was observed using an L band range (200nmi) air-route surveillance radar (ARSR). It is shown that the measured clutter amplitudes obey a Weibull distribution.

Elichi Kiuchi

Papers

On Weibull-Distributed Weather Clutter