Detection of a manoeuvring air target in sea-clutter using joint time-frequency analysis techniques

Traditionally, radar signals have been analysed in either the time or the frequency domain. Joint time-frequency representations characterise signals over a time-frequency plane. They thus combine time-domain and frequency-domain analyses to yield a potentially more revealing picture of the temporal localisation of a signal´s spectral components. Therefore, for air target returns with time-vary ing frequency content, joint time-frequency representations offer a powerful analysis tool. A concise review of time-frequency transforms is provided as background and is needed to appreciate how time-frequency processing methods can improve conventional time or frequency processing methods. The authors use time-frequency analysis techniques for the detection of a manoeuvring aircraft using high frequency (HF) radar in heavily cluttered regions. They compare the ability of different time-frequency transforms to resolve several experimental aircraft returns. The relative speeds of the different transforms are also quantitatively studied. The results clearly demonstrate that time-frequency analysis techniques can significantly improve the detection performance of the HF radar and add considerable physical insight over what can be achieved by conventional Fourier transform methods currently used by HF radars.