Standard radar is strictly line of sight. It's like using a searchlight. The radar transmitter illuminates the target and some of the energy is reflected off the target back to the receiver where it is "seen". Should the target be over the horizon it is just out of view.
Down under, the Jindalee system uses extremely low frequencies, at least low for a radar. The Aviation Week article didn't mention the frequencies used, but its got to be 10 meters or longer. CB band and below. At low frequency the ionosphere acts as a mirror and reflects the transmitted pulse back down to the ground far beyond the horizon. The Australians have constructed three low frequency over-the-horizon (o-t-h) radars spread across their sub continent, looking northward, covering the sea between Australia and Indonesia.
O-t-h radar, since it reflects off the unstable and fluxuating ionospheric mirror, suffers from image distortions, blind spots, and difficulties computing range. You might say the picture is blurry. But usable. And operating three radar stations has got to be cheaper than flying reconnaisance, or launching recon satellites.
I notice that the o-t-h radar covers the sea areas in which they are still looking for that lost Malaysian airliner, the one that dropped off radar and was never heard from again. Could the searches be guided by Jindalee o-t-h radar tracks?
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