Radio has come a long way since Marconi bashed a telegraph key and radar was just a squiggle on a cathode tube, but despite a century of advances, they’re still prone to the same problems as the first pioneers encountered. For five days in July, the Office of Naval Research’s (ONR) Research Vessel (R/V) Knorr made a survey in the waters off Virginia Beach, Virginia using ScanEagle UAVs to study the effects of oceanic and atmospheric changes on radar and radio waves with the aim of producing more secure military communications and improving the ability of radar to detect hostile craft.
Radio wave propagation is a very basic phenomenon of broadcasting. If you were to set up a radio broadcasting station on the Moon, the radio waves would broadcast out like light from a bulb. That means that the signal sent out would be almost entirely by line of sight and any object opaque to radio waves would shadow it almost entirely.
On Earth, this doesn't happen quite as often. You can be out of sight of the transmitting antenna or even on the other side of the planet and still be able to receive a broadcast. As radio waves spread out, they interact with the atmosphere, so that instead of simply moving in a straight line, they are bent or bounced back depending on their wavelength. It’s what allows you to pick up broadcasts even though the transmitter’s antenna may be obscured or even below the horizon. It makes local broadcasting practical and makes it possible for a yachtsman in the South Pacific to talk to someone in New York.
This phenomenon is one that broadcasters rely upon, but it also causes a lot of problems. Since the propagation of radio waves is dependent upon the atmosphere, this propagation changes according to time of day as the Sun heats the atmosphere and radiation from space charges the upper layers.
An example of this change was the way that British teenagers in the 1960s would stay up late waiting for the right conditions to pick up broadcasts of pop music from Radio Luxembourg on the Continent. A more prosaic annoyance is how broadcasts from other regions could suddenly interfere with ones close by. It’s one of the reasons why ham radio operators were given high frequency bands in order to avoid interfering with long and medium wave broadcasts reserved for state and commercial broadcasters.
Such problems are also the reason why the military, and hence the ONR, are interested in studying these effects. What interferes with civilian broadcasts does the same to military ones as well, potentially leading to signals intended for friendly ears reaching hostile ones as well.
Worse, since radar is a form of radio, this is affected as well. Beams intended to catch an approaching enemy can be sent shooting into space instead of heading for their target. Because the military must act in all terrains, at all times of day, in all parts of the world, it needs a comprehensive understanding of what is going on.
Radio propagation varies according to the nature of the atmosphere and how it interacts with the surface of the Earth over land or sea. It’s a complex phenomenon that involves many interacting factors to produce the reflection and refraction, which are called “ducting.”
“We need to understand where we are in relation to this ducting environment and understand the energy we’re emitting and the energy an adversary is emitting,” says Dr. Dan Eleuterio, program officer for ONR’s Ocean Battlespace Sensing Department. “If we don’t know these things, it’s like rolling the dice. If we do know them, it can give us a tactical advantage.”
The study of radio propagation requires real-time data telemetry to collect the needed data. Previously, this would be done from the ground or using balloons. Ground observations are limited and balloons can’t be steered and are difficult to use at low altitudes. The ONR survey was carried out by ScanEagles and unmanned submersibles and surface craft, which can be placed in a specific area and remain there for long periods collecting data, especially at low altitudes.
According to ONR, the ScanEagles carried sensor packs developed by the Marine Physical Laboratory at Scripps Institution of Oceanography that measured environmental factors such as surface waves, wind speed and direction, humidity and temperature, which were transmitted to a nearby destroyer or an amphibious assault ship.
“In the old days, we launched weather balloons to give us the best data on the real environment, but that only happened in one place and at one time of day,” says Cmdr. Rob Witzleb, head of capabilities and requirements on the staff of the Oceanographer of the Navy. “Many miles and hours later, we were often left looking for answers when weapon systems didn't perform the way we thought they would. Using UAVs is giant leap forward in that they can give us near-continuous data, across multiple parameters where the atmosphere is the most unpredictable.”