Heavy fog affects nearly all kinds of transportation: from pedestrian-driven vehicles to airplanes. And sometimes, it can even be downright dangerous.

So detecting fog is important, but existing systems are costly and not very accurate. They use expensive satellite systems, which aren't even on the ground where detection is most important.

However, scientists at Tel Aviv University in Israel, recently discovered that the wireless microwave transmissions of cellular towers can detect heavy fog, and newer high frequency towers can even detect instances of light fog.

The best thing about this method of fog detection is that it doesn't require any new technology. Cellular towers span the world and with a steady push from consumers for even more data usage, cellular providers are beginning to install new high frequency towers in more places.

"The goal of the work presented here is to reveal the potential that exists in commercial microwave systems, where higher frequencies more sensitive to fog are starting to be used," says Professor Pinhas Alpert. "We are presenting a window of opportunity to monitor fog with high resolution using technology already in place."

Cellular towers transmit wireless microwave transmissions at ground level: this means that atmospheric changes affect the transmissions. One such change is fog. Most current towers operate at frequencies of up to 40 gigahertz, which means they can easily detect heavy fog. However, lighter fog is harder to detect. But thanks to new technology and a higher demand for bandwidth among consumers, cellular providers are putting up new towers with higher frequencies, of up to 80 GHz, in more areas, and those frequencies have a higher sensitivity to light fog.

Researchers tested their theory by using cellular towers in Israel and calculating the level of water content in the atmosphere that they could detect through the city's cellular towers' microwave transmissions. Researchers worked with three different frequencies: 20, 38 and 80 GHz. As expected, the 80 GHz frequency detected the lightest of fogs (with visibility at about ½ mile). However, at 38 GHZ, the researchers only detected heavier fog density.

The researchers' experiment, though, matched up to their fog detection theory.

"While most studies of this kind are focused on rainfall, fog is no less hazardous to people and objects in motion," says Dr. Noam David of the university's Department of Geosciences. "Current monitoring tools are insufficient. Our new approach exposes the potential that already exists in these communication systems to provide high-resolution spatial measurements of fog."