A.G. Stove

Passive bistatic radar experiments from an airborne platform

The initial analysis of data collected during the airborne experiments has demonstrated airborne passive radar operation, using commercial FM radio signals as illuminators of opportunity, and these are believed to be the first results of this kind. The results have highlighted several practical techniques for improving the system performance: using multiple perspectives, optimal illuminator modulation bandwidth, and multiple looks over time.

Analysis of sea clutter distribution variation with Doppler using the compound k-distribution

Sea clutter is the backscattered returns received by a radar system from the sea surface. Maritime radar signal processing has the ability to partially compensate for clutter to achieve effective detection of targets on or near the sea surface. This paper investigates the fit of the compound k-distribution model to sea clutter amplitude statistics, within individual Doppler bins across the Doppler spectra. The data used was recorded with a monostatic coherent X-band radar on an airborne platform; both horizontally and vertically polarized data has been analysed. The statistics of the sea clutter distributions have been evaluated using the probabilities of false alarm (PFA), which are the calculated from the sea clutter cumulative amplitude distributions. These curves are plotted as a function of detection threshold. K-distributions have been fitted to the PFA of the sea clutter across the Doppler spectrum. The variation of the fitted shape parameter with Doppler bin has been used to identify the relationship between backscattered sea clutter and Doppler. The results show a clear variation with Doppler of the shape parameter obtained from the fitted distribution. The variation is also found to change with polarisation.

Application of a new sea clutter Doppler model

This paper applies a recently developed sea clutter Doppler simulation model to five sets of data selected from the CSIR 2007 sea clutter database. Each dataset is characterised using the parameters required for the new simulation model. These parameters are then compared between datasets, before the model is then used to generate spectra for each dataset. The effectiveness of the model is discussed and evaluated through comparing the statistics of the simulated data to the real data. It is shown that the fit is suitable for modelling of clutter characteristics that can then be used to understand likely detection performance in a radar. A linear relationship is also shown between two of the parameters used, which shows that it might be possible to reduce these to a single independent parameter.

Measurements of bistatic radar sea clutter

Bistatic radar is a technique of considerable potential importance and interest. Despite this, current understanding of the properties of bistatic clutter, and in particular, bistatic sea clutter, is limited at best. We present some results of a recent trials campaign to gather bistatic sea clutter data, and to analyse the data in order to develop models to represent bistatic radar sea clutter. The results indicate that the shape parameter of the compound K distribution model fitted to the data tends to be higher for the bistatic clutter than for the equivalent monostatic clutter. This suggests that a bistatic geometry may allow a lower detection threshold for a given probability of false alarm, and hence give improved detection performance of weak targets against a clutter background compared to the conventional monostatic geometry.

Use of the Kullback-Leibler divergence in estimating clutter distributions

This paper investigates the application of the Kullback-Leibler divergence (KLD) to quantify the loss in detection performance associated with misestimating clutter distributions. The problem of detecting targets in long-tailed clutter is presented. The significance of the KLD as an information theoretic measure to enhance the accuracy of threshold setting is discussed. The behaviour of the KLD is shown by comparing K-distributions with different shape parameters, since this distribution is known to be a good fit to clutter, particularly to sea clutter. The KLD is compared with the difference in Probability of False Alarm, threshold and other ad hoc measures of the accuracy of the fit. The KLD is then used to analyse the quality of the fit to the K-distribution of the statistics in different Doppler bins of a coherent sea clutter spectrum. The paper concludes that the KLD is better than the ad-hoc measures for determining the cost of misestimating the distributions, although some ad-hoc measures can give results that are close to it.

Issues with consistent generic representations of a radar

This paper discusses whether truly generic representations of radars, or other sensors are possible. It concludes that they are probably not, because the abstractions which have to be made in order to be able to reason about their capabilities will inevitably over-simplify the description for other purposes. Examples to support this contention are drawn from the way radar terminology is used. The possible implications of such a conclusion on the use of a dasiasemantic Webpsila approach to allow sensors to understand each other and hence interact autonomously, are discussed.

A compact, formalized description of radar architectures

This paper discusses a way of describing radar architectures using descriptions derived from the formal (Backus Naur) descriptions of programming languages. Examples of such a language are given, together with examples of how radars could be described by it. The use of such a scheme to link together models of the radar and prove the correctness of its operation are discussed.

Radar considered as a fine art

This paper argues that radar research is in many cases becoming a separate discipline from the development of the technologies used to design and manufacture radars. It argues that it is better that this separation is recognised for what it is rather than pretending it does not exist. Instead, it argues that this separation can be the stimulus for developing new ways of assessing radar designs which although not directly related to a customers explicit requirements, may yet lead to the design of better radars in the longer term.