Jindalee Project Proceeding On Target

Jindalee radiates a strong pulse of electrical energy in the high frequency band, approximately the part of the spectrum that is used for short wave radio broadcasting. The pulse goes up to the ionosphere and it reflects back to earth to “illuminate” the earth’s surface at a considerable distance from the transmitter. If there is a ship or an aircraft in this zone, the “target” reflects a tiny pulse back to the ionosphere, which in turn bounces down to a receiver. High speed computers sort out the very weak reflected signal from the clutter ofbackground noise, and identify it by speed and direction as either a ship or a plane, then display it as a symbol on a monitor.

The trick to Jindalee is that the system “looks into” various areas of interest, which are searched one by one. A typical search area could be about 50km by 100km. To select that patch of the earth (or more probably sea) depends on the frequency of the wave used and the height of the ionosphere at that moment. If the return is weak and doubtful, the operator can call up recorded returns and display them consecutively in a ladder progression on a screen. The target “blip” is identifiable. Obviously ifit is present in a series of displays, its position and its speed can be calculated.

According to Dr Malcolm Golley, acting chief of the high frequency radar division of the SRL, location can be “down to 10 nautical miles” (18km). Accuracy varies with the distance of the target, the frequency used and the conditions generally. There is no height information.

These accuracies mean there is still a requirement for some form of airborne radar system, for precision vectoring of intercepts. Accuracy of a microwave radar would be 100 times greater than Jindalee; however, Jindalee’s coverage is more than 100 times greater than even an airborne microwave radar.

Jindalee’s frequency management system constantly monitors the state of the ionosphere to select the frequencies that will look into the zones of surveillance interest at any one time. When the network is up and running, the total area covered will include the coast from about Carnarvon, WA to Cooktown, Qld and out for distances up to 300km. Coverage routinely extends into the South China sea north of Borneo.

At the same time, broadband receivers constantly monitor the broad range of frequencies which are in use, for instance for civil or military communications. Even though some bands may show no operators on them, they are totally blocked off, for instance the channels used for international distress.

This contrasts with the Soviet 0TH experiments some years ago when the characteristic “woodpecker” signals drowned out any other users unfortunate enough to be on the air on the frequencies selected.

When the system selects the frequency band required and finds an empty frequency within that range, the pulse is sent out. The whole process occurs-and can be varied- in milliseconds. The frequency hunting system can also be used to detect jamming and to change frequencies to avoid it.