High-frequency Active Auroral Research Program

The High-frequency Active Auroral Research Program (HAARP) is a University of Alaska Fairbanks program which researches the ionosphere – the highest, ionized part of Earth's atmosphere. The most prominent instrument at HAARP is the Ionospheric Research Instrument (IRI), a high-power radio frequency transmitter facility operating in the high frequency (HF) band. The IRI is used to temporarily excite a limited area of the ionosphere. Other instruments, such as a VHF and a UHF radar, a fluxgate magnetometer, a digisonde (an ionospheric sounding device), and an induction magnetometer, are used to study the physical processes that occur in the excited region.