Analysis of Heavy Radar Clutter

Abstract

Radar clutter denotes unwanted echoes from the natural or artificial environment, implying that these echoes hinder from detecting wanted targets in received radar echoes. To overcome the difficulties caused by clutter in terms of detecting a target, it is essential to understand the characteristic of radar clutter and reduce the clutter component in received radar echo, especially in case of heavy clutter. In this dissertation, two types of heavy clutter environments are discussed: sea clutter and clutter in an indoor environment. First, sea clutter measured by X-band (normally 8 to 12 GHz) radar with high range-resolution at low grazing angle is analyzed by exploiting probabilistic models. In low range-resolution radars, the statistical characteristics of sea clutter are generally similar to those of noise, which follow the Rayleigh distribution. However, the statistical distributions of sea clutter may depart from a Rayleigh distribution for high-resolution radars at low grazing angles. In addition, an important characteristic of sea clutter measured using a high range-resolution radar is the occurrence of sea spikes, which are intermittent signals with unexpectedly large amplitudes. The spikiness can be shown by the heavy-tailed statistical model and the amount of sea spikes in a received signal. Statistical analyses using sea clutter data with high range-resolution measured at low grazing angle are discussed in terms of sea state, polarization, and range-resolution. As a result, the spikiness of sea clutter increases as the range resolution becomes finer, in high sea state with horizontal polarization. The statistical analysis could be utilized to generate clutter signal in Monte-Carlo simulation which gives the performance prediction in terms of detecting a certain target in heavy sea clutter environment. Next, clutter analysis in an indoor environment for the detection of human is discussed. Real indoor environments provide heavy clutter components and spurious ones due to multipath effects. These clutter components cause a serious problem, i.e., a strong false alarm in detecting a human, especially an individual lying down with very low radar cross-section (RCS). In this dissertation, clutter caused by an indoor environment is systematically analyzed and the result of clutter reduction methods in terms of detecting a standing individual and an individual lying down is investigated. Based on this analysis, the robust detection method to determine the presence of individuals in an indoor environment by exploiting an impulse-radio ultra-wideband (IR-UWB) radar. Even after clutter reduction, the detection of an individual lying down continues to pose a challenge. Thus, we devised a novel two-stage detection scheme that first involves detection in the range domain, and then in the frequency domain, thereby resulting in good detection performance in terms of a high detection rate and a low false alarm rate. The proposed method was demonstrated by several experiments with various scenarios in indoor environments, and the results indicate that its performance is robust in various scenarios.