A Defence Science and Technology Organisation (DSTO) developed software system will allow the Royal Australian Navy to optimise the performance of its radar and communications systems when confronted with meteorological conditions known as ducting. Ducts can cause radiowaves to propagate to anomalously long or short ranges. Ducting is a very common phenomenon in the first few tens of metres over the oceans surrounding Australia. In addition, elevated ducts commonly occur at heights of hundreds or thousands of metres above the surface.
TREPS, the software known as the Tropospheric Refractive Effects Prediction System, exploits atmospheric meteorological information, such as air pressure, temperature and humidity, to model where atmospheric ducts occur and how strong they are. The software uses this ducting information to predict the effects on microwave propagation and the performance of radar and other microwave systems. The significance for defence is that radio waves, such as radar, can be trapped in a duct and propagate along a path following the curvature of the earth's surface, instead of travelling in a straight line. This bending of the radio wave path is caused by the refractive properties of the atmosphere and sometimes results in waves bouncing along the sea surface for long distances. Maximum radar detection ranges against low flying targets, such as sea-skimming missiles, are strongly influenced by the heights of both the radar and the target in relation to the height of the duct. Electronic support measures (ESM) systems are also affected in a similar way. Most ships have several radar and ESM systems capable of detecting an incoming sea-skimming missile. Since these systems are generally fitted at different heights above sea level and operate at different frequencies, they are affected differently by given ducting conditions.
Consequently, for the warfighters aboard RAN ships, TREPS can determine which radar or other system aboard ship is best suited to detecting and tracking targets. All shipborne radiowave systems, including radar, ESM, navigation and communication systems, are potentially subject to ducting effects if directed towards the horizon. More information: DSTO contact Mr. Steve Butler