Smugglers can run but they can't hide

"Gypsy” sees clearly through ionospheric distortion.

5 Ratings

Imagine you are the pilot of a DEA enforcement plane sent to find a small drug-smuggling aircraft over the Caribbean. Using your onboard radar would alert the well-equipped smuggler to your presence; he would just drop the cocaine overboard and later return with a new shipment. You fly high, hoping to catch a glimpse of the small plane. But there are miles of ocean in every direction.


The pilot has filed no flight plan and is flying low to avoid microwave radars on the distant coast. The drug-smuggler is confident that no enforcement agency has a clue where he is. The technology that could detect him doesn't exist. As he approaches the drop zone, he sees the pick-up boat getting in place to receive his cargo. But what’s this! A Coast Guard vessel is speeding toward the drop point. And suddenly there is an enforcement plane at his side signaling instructions to divert to the shore to land. How could they have discovered him? How did they know exactly where he was? A mystic seer, perhaps?


Observing and intercepting an airplane over the vast ocean is like finding a needle in a haystack. Two things are required, wide area surveillance and accurate geolocation. Over-the-Horizon radar (OTHR) operates by reflecting radar waves from the ionospheric “mirror in the sky," providing wide area surveillance for detecting airplanes and surface vessels over continental-size regions. But detecting the targets is only half the battle; the targets must also be geolocated in order to be intercepted. This requires accurately characterizing the changing ionospheric mirror in real time. Without accurate geolocation, even detected adversaries will escape. The existing geolocation tools are limited to representing ionospheric variations in range and height, while only taking in vertical and oblique ionospheric soundings. Significant target geolocation errors can arise due to un-modeled cross-range ionospheric tilts. With the new GPSII ("gypsy") technology, the ionospheric model is fully three-dimensional and can utilize several novel forms of ionospheric data, including radar measurements of known references and GPS transmissions.


An AFRL scientist recognized the opportunity to improve ionospheric modeling by assimilating additional types of ionospherically-related data beyond those conventionally used. Scientists at NWRA had already developed a similar capability for a UHF Early Warning Radar application. The algorithm at that time primarily assimilated GPS transmissions and vertical electron density profile information. We saw that GPSII could be straightforwardly modified to assimilate conventional backscatter soundings as well as additional information like radar measurements and oblique ionospheric soundings, so it was the perfect starting platform for collaborating with the AFRL.

"NWRA appreciated the overarching AFRL research plan and was willing to work closely with AFRL in an integrated approach to transition contracted studies towards operational implementation." — Dr. Leo McNamara


Short wave radio bounces High-Frequency (HF) signals from the ionosphere to communicate beyond the horizon. Why not do the same thing with a radar? Over-the-Horizon Radar (OTHR) transmits waves in the HF band to illuminate targets 500 to 5000 km away using the mirror-like reflection property of the ionosphere, an ionized region of the atmosphere peaking at around 300 km in altitude. But this mirror is dynamically changing and wiggly, so it is not always easy to determine where the illuminated targets are geographically. Scientists at NorthWest Research Associates developed software that can model the dynamic ionosphere well enough to geolocate the OTHR targets by assimilating several types of ionospheric data. The capability is called GPSII, pronounced “gypsy” and stands for GPS ionospheric Inversion. As the name implies, GPSII assimilates data derived from GPS signals, but the algorithm can also use several other forms of data. Under the OTHR Metric Accuracy effort, GPSII was extended to use ionospheric probing measurements routinely collected by OTHR called backscatter ionograms.


The extension of GPSII's assimilation capabilities developed under this SBIR has either directly resulted in or figured heavily in nearly $4.5 million of new contract funding. GPSII has expanded our business opportunities from DoD into the intelligence community.

GPSII is currently being demonstrated on a US Government radar asset. The project has also transitioned to an intelligence community application and is showing unprecedented metric accuracy improvement.

NorthWest Research Associates

Redmond, WA

NWRA is a scientific research group, owned and operated by its Principal Investigators, with expertise in the geophysical and related sciences. We provide an environment for unencumbered science, in which scientists and engineers can achieve excellence in basic and applied research.

Dr. L. J. Nickisch Dr. L. J. Nickisch

Dr. L. J. Nickisch

Senior Research Scientist, Vice President

Dr. Sergey Fridman Dr. Sergey Fridman

Dr. Sergey Fridman

Senior Research Scientist

Dr. Mark Hausman Dr. Mark Hausman

Dr. Mark Hausman

Senior Research Scientist


High Frequency Over-the-Horizon Radar Metric Accuracy





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