Centre for
Centre for Space Physics

Doppler clutter in HF radar systems


HF (3-30 MHz) radar systems transmit signals that propagate up to the ionosphere which are deflected back to Earth. These are over-the-horizon radars and are used for long range surveillance and for ionosphere research. The timing of a target echo is used to determine location, while the Doppler effect is used to extract target speed information. This assumes that the target is the only source of motion for the Doppler shift. However, temporal variations of the ionosphere electron density superpose an additional Doppler shift onto the returned radar echo, adding Doppler clutter. ULF waves induce Doppler clutter in over-the-horizon radar systems of the same order as might be detected by ship movements.

The Space Physics group are conducting research into the properties and reduction of Doppler clutter caused by ionsophere variability. In collaboration with LaTrobe University, we analyse the data from the Australian SuperDARN radars, and the magnetometer data from Macquarie Island, in addition to HF ray tracing and ULF wave models.