Overcoming ignorance of terrain for predicting signal strength
Terrain affects communications signals and other electromagnetic waves, but topographical maps are simply not precise enough for planners to predict signal strength in many cases, according to Gary Brown, a remote sensing expert and director of ECE’s ElectroMagnetic Interactions Laboratory.
“The loss of signal strength on a communications path that travels over terrain is currently unknowable, yet there are a number of users – commercial and military – who really need this information,” he says.
Brown’s team has developed a quick, memory-efficient method that helps solve this problem and is applying it to help the National Radio Astronomy Observatory (NRAO) in Green Bank, W.V. maintain its radio quiet zone.
Other users who need similar data include military patrols heading into unknown territory who need to stay in constant communication and military spectrum planners trying to avoid friendly radio interference over a given land region, he says.
The problem, Brown says, stems from the relatively low resolution of topographical information. Topographical data points are seldom closer together than 30 meters, he explains. The elevation in rough terrain can change significantly between 30-meter-apart measurements from features such as steep ravines, rock outcroppings, and small hills.
Brown’s team quantifies the level of uncertainty in predicting the path attenuation. “Based on probabilities of what we know about the roughness, we can provide an average attenuation loss and a standard deviation. If we need more precision, we can target an area for gathering more topographical data.”
Brown is working with federal agencies to help eliminate interference signals at the Green Bank Telescope from other locations in the National Radio Quiet Zone. “With more precise understanding of how signals travel in the zone, regulators can allow or prevent other radios from coming online,” he says.
The Army Research Office and Naval Surface Warfare Center are providing funding for the effort.