As terrible as war is, it often brings scientific discoveries to the masses in peacetime. One such discovery from World War II is the Sound Fixing and Ranging channel, or SOFAR channel for short.  It's not a TV channel, but an ocean channel. In 1944, geophysicist Maurice Ewing discovered a hidden horizontal oceanic layer about 1,000 meters (3,300 feet) deep under the ocean's surface. It's sandwiched between warm, less salty and lighter upper waters, and cooler, more salty denser lower waters. What's unique about this layer is its ability to trap sound waves and channel them over vast distances.

The sounds that are trapped are very low frequencies (infrasound), mostly from explosions, eruptions, and earthquakes. These infrasounds travel very slowly along the channel, staying within the upper and lower boundaries, much like a boat cruising through a canal. Sounds are heard by dropping a hydrophone (a microphone that works under water) into this channel.

In the first tests of SOFAR in 1944, scientists clearly heard a controlled explosion more than 900 miles away. During the war and since, the SOFAR channel is used by navies to listen for submarines, by oceanographers to listen for whales, and by geologists to listen for volcanic eruptions and earthquakes. It's difficult to pinpoint the location of infrasound events because the SOFAR channel slows sound waves down, so data from several monitoring stations is used for triangulation.

Ewing also theorized that the atmosphere may have its own SOFAR channel. After the war, he headed up a top-secret mission named Project Mogul that was tasked with listening for Soviet nuclear weapon atmospheric tests. The search started in the tropopause, the boundary between the lower troposphere and upper stratosphere. The tropopause is about 10 to 20 kilometers above the earth's surface (33,000 and 65,000 feet). The tropopause is thought to behave similar to the ocean's SOFAR channel, trapping infrasounds within its boundaries.

Project Mogul was so secret, that records of its existence didn't materialize for 50 years after it's inception. The project was short-lived, but one of its experiments fueled one of the most famous conspiracy theories in human history – the Roswell UFO crash. In 1947, one of Project Mogul's balloons crashed near Roswell, New Mexico. What followed was a back-and-forth by the Army and government officials with the press, first admitting that a "flying disc" crashed, then denial. The news articles with the picture of an Army officer kneeling next to a shredded silver balloon carcass seem to back up what Project Mogul was all about – determining "the velocity and direction of winds at high altitude."

Now the search for an airborne SOFAR channel has been resurrected, in New Mexico of all places. Sarah Albert, a geophysicist at Sandia National Laboratories, uses solar-powered balloons with wireless telemetry that can float within the tropopause, listening for distant sounds. In April of 2021, Albert's team released a test balloon in Albuquerque, New Mexico and successfully captured the sound of the launch of Blue Origin’s New Shepard rocket 250 miles away in Texas. It was the first verified instance of detecting distant infrasounds in the atmosphere while airborne.

They also heard a sound of unknown origin that repeated several times an hour. A later experiment with another rocket launch was unsuccessful. These inconsistent results have scientists theorizing that the SOFAR channel in the atmosphere is not always present. It may also be susceptible to drastic changes from winds, temperature variations, and the delicacy of the atmosphere. Fundamental principles of physics support this theory: Sound travels more efficiently through water and solids; Air, especially at 60,000 feet, is very thin and highly inefficient in carrying sounds. 

Sarah Albert is convinced that the atmo-SOFAR channel exists, but is not as stable as the oceanic SOFAR channel. Experiments are ongoing to determine the best altitudes and conditions for using the atmo-SOFAR channel effectively. Another tool to detect and warn of a distant catastrophe can only benefit our planet. Who knows, the atmo-SOFAR channel may warn us of of an honest-to-goodness visit form a flying saucer.