WASHINGTON, 5 June 2011. Surveillance and reconnaissance experts at the U.S. Intelligence Advanced Research Projects Activity (IARPA) in Washington will brief industry June 23 on a project to enhance signals intelligence capability to pinpoint high-frequency (HF) radar and communications systems anywhere in the world.

Many RF signals, such as VHF and UHF, are relatively easy to locate because they are largely line-of-sight, meaning they travel only in straight lines. They cannot easily penetrate barriers such as tall buildings and mountain ranges. No so HF radio signals.

HF radio waves -- as any Ham radio operator or shortwave radio listener can tell you -- are particularly difficult because they not only follow line-of-sight paths, but they also bounce off of layers Earth's upper atmosphere called the ionosphere and come back to the Earth's surface where antennas tuned to HF frequencies -- roughly 2 to 30 MHz -- can pick them up.

HF signals are particularly prone to interference because antennas literally can receive their signals from different directions and at different times because of the ionospheric bounce phenomenon. The ionosphere is ionized by solar radiation and helps propagate HF radio signals to distant locations, hence the long distances that shortwave and Ham HF radio signals can travel.

HF radio signals, due to their nature, also are exceedingly difficult for signals intelligence systems to geolocate and characterize accurately, and this is the goal of the IARPA HFGeo program. Ionospheric variation,high noise levels, and ionospheric polarization rotation, multipath induced signal fading, and simultaneous multiple angles-of-arrival will make this job challenging.

The IARPA HFGeo program seeks to capitalize on advances in high-dynamic-range receivers, antenna techniques, adaptive signal processing, and ionospheric ray path prediction, and improved measurement and modeling techniques to geolocate HF emitters around the world, as well as determine if these signals are involved with benign commercial activity, or are part of hostile communications and radar systems.

The goals of the IARPA HFGeo program include developing the ability to resolve multiple angles-of-arrival and polarization states accurately through novel antenna concepts; enhance signal-to-noise ratio and signal detection with multi-dimensional adaptive signal processing; determine the state of the ionosphere accurately; and integrate these technologies into geolocation and source characterization applications.

The HFGeo proposers' day conference will be from 8:30 a.m. to noon Thursday, 23 June 23 2011 in the Washington, D.C. area. Those interested in attending must first register to get access to the proposers' day Website, which has the event agenda, location, directions, security, and lodging information. The deadline for registering is 17 June 2011. Register online at https://conference.brtrc.com/HFGeo_pd/Registration/Register.aspx. No walk-in registrations will be accepted.

For questions or concerns about the IARPA HFGeo proposer's day conference, contact IARPA's Frank Robey by e-mail at iarpa-events@ugov.gov. For questions about the HFGeo program itself, contact IARPA by e-mail at dni-iarpa-baa-11-07@ugov.gov.

More information is online at https://conference.brtrc.com/HFGeo_pd/Overview.aspx.