The positive classification and identification of airborne targets beyond the visual range by using the reflected radar signal has become an increasingly valuable capability for the defence force of a country. The rotating structures on an airborne target cause additional Doppler modulation in the return signal which is known as the micro-Doppler effect. Information regarding the rotating structures can be extracted from this effect.
A technique based on time-frequency and tomographic analysis is introduced in this research to extract certain helicopter blade parameters which will aid in the identification of a helicopter. The proposed algorithm shows that (under certain conditions) it is possible to extract the number of main rotor blades, the blade length and the rotation rate of the helicopter’s main rotor. These features can be used to determine the make and model of a particular helicopter.
The methodology followed in this research was a) to develop a point scatterer model to simulate the micro-Doppler effects from the helicopter and b) to develop a blade parameter extraction algorithm based on the simulation model. Finally this algorithm was validated by means of results obtained from measured radar data from several different military helicopters.
The algorithm was designed for a pulse-Doppler tracking radar, and the results achieved was encouraging in the sense that reliable results have been obtained for ranges up to 14 km.