Time-frequency methods in radar, sonar, and acoustics

Abstract

The fields of radar and sonar are traditionally key application areas and testing grounds for advances in signal processing, including time-frequency (t,f) methodologies; their significance is demonstrated in seven sections.

This chapter begins by considering a baseband Doppler radar return from a helicopter target. For such signals, a linear (t,f) representation provides a high resolution suitable for preserving the full dynamic range (Section 14.1). It is then shown that the synthetic aperture principle allows the combination of range resolution, achieved by the use of linear FM signals, with cross-range. For long observation intervals, the phase cannot be assumed to be a linear function of time; then (t,f) based imaging can obtain improvements in focus of the synthetic-aperture image (Section 14.2). In another illustration, it is shown that when a propeller-driven aircraft or a helicopter passes overhead, it produces a Doppler effect which allows the estimation of flight parameters by using IF estimation and the (t,f) interference patterns formed in TFDs (Section 14.3). An example is then presented which shows that to track a theater ballistic missiles launch, the WVD can be used effectively. Its peak provides a direct estimate of the instantaneous Doppler law giving the accelerating target dynamics (Section 14.4). It is then shown that in sonar, there is a clear rationale for using (t,f) processing of reflected signals to provide useful information about targets such as ships (Section 14.5). Sparse (t,f) distributions are then applied to geophysics acoustics (Section 14.6) and a concise tutorial review of (t,f) audio processing for speech and underwater acoustics applications indicates that high-resolution TFDs can result in much improved performance (Section 14.7).