Kirtland Air Force Base, N.M. -- Atmospheric data gathered by a radio transmitter in Alaska is currently helping a joint Air Force and Navy research team based here determine how warfighters might get clearer communication with aircraft, ships and satellites in the future.
The High Frequency Active Auroral Research Program, known as HAARP, is a joint program through the Air Force Research Laboratory that investigates ionospheric physics and radio science. The program was recently featured in a Feb. 24 Pentagon Radio podcast of "Armed with Science."
The ionosphere is a region of the upper atmosphere where there are a significant number of charged particles, said Todd Pedersen, a senior research physicist at the Air Force Research Laboratory.
"Energy from the sun, particularly in the ultraviolet wavelengths, strikes atmospheric gas molecules and atoms with enough force to dislodge electrons," he said. "This results in a field of negatively charged electrons and positively charged atoms and molecules [ions], maintained in a plasma state. This conducts electrical currents and responds to electric and magnetic fields."
This ionospheric study is of particular interest to the Department of Defense because it affects the positioning of and communication with military assets.
James Battis, HAARP program manager at AFRL, said the AFRL radio transmitter in southern Alaska consists of 180 transmitters with a frequency range of 2.65 to 10 megahertz, and sends high-frequency signals into the ionosphere.
"These are the transmissions which are used to communicate with aircraft and satellites, so the Air Force is interested largely in effects of the ionosphere on communications," Mr. Battis said.
Mr. Battis said that when the signals from a GPS leave a satellite, their paths are actually deflected by the structure of the ionosphere, sometimes resulting in GPS errors "due to distortions created by the ionosphere."
"While these errors may not be significant to the average user, they can be significant for precise military positioning, and that's one of the reasons [the Defense Department] is interested," he said.
Similarly, the Navy uses the transmissions to communicate with its fleet.
"We have ships all over the globe that we want to be in contact with at all times, so any effect the ionosphere has on communications is something that we want to study," said Craig Selcher, HAARP program manager at the Naval Research Laboratory.
Mr. Battis said that the research conducted by HAARP will also benefit civilian communication systems as well, including those supporting civil aviation and ground communications.
"Satellite radio and satellite television can also be impacted by naturally occurring ionospheric conditions," Mr. Selcher said. "And trying to understand those is to begin to learn to predict, and maybe to ameliorate, the problem."
Mr. Battis said that charged particles affect radio waves passing through the ionosphere and can affect things like the quality of the signal from a satellite to the ground, or short-wave communications from ground to ground.
Signals from satellite-based surveillance and positioning systems also can be affected by the ionosphere, he said.
Mr. Battis also described much of the previous ionospheric research as passive, with the evaluation of ionospheric effects based on the quality of reception of a normally transmitted radio signal.
"The radio waves we transmit from the array at our facility actively create processes and interactions with the particles in the ionosphere," he said. "Hopefully, we can learn what the responses are and how to use them to improve transmissions through the ionosphere," he said.