Overview

Classification and possibly identification of observed radar targets is a natural requirement for radar systems applied for air or maritime traffic control and defence. In all cases without target information, for example provided by secondary surveillance radar (SSR) or with identification of friend or foe (IFF), the radar echo signal has to be evaluated. For air surveillance it is of great importance to distinguish as fast as possible between targets of interest, such as airplanes, and false targets like birds or flocks of birds. By this distinction the formation and processing of false tracks, thereby wasting computer and radar time and power is avoided.

Possibilities and some results for radar imaging of targets have been discussed in chapters 14 and 15. Target imaging is, of course, the most advantageous method for classification. In cases where this is not possible, other methods for classification may be applied.

Attempts have also been made to use the echo series of a target for target classification. The echo series of airplanes is influenced by typical internal motion, vibration or rotation. Vibration and rotation effects cause a signal fluctuation and modulation in contrast to an ideal point target. In particular, the rotation of propeller and jet engine cause modulation of the echo signal. These fluctuation and spectral effects can be used if the radar waveform is chosen suitably to perform adequate sampling. With a phased-array multifunction radar we can use the freedom of waveform selection and dwell time to evaluate these effects adequately.

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