High up in the ionosphere, plasma bubbles invisible to the naked eye wreak havoc on communication and navigation systems back on Earth.
Instabilities in the bubbles often cause over-the-horizon radars to either lose signals or to register readings from different regions than where they should be looking. GPS receivers can fail as these structures pass overhead.
Scientists, who have been studying the phenomenon for decades, are stymied about why the bubbles develop one night but fail to materialize under similar conditions the next night. CSL researcher Jonathan Makela hopes to change that through the Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) project.
“These instabilities can really affect the reliability of critical satellite navigation and communication systems,” said Makela, a professor of electrical and computer engineering at the University of Illinois. “Our hope is that RENOIR goes a long way in answering some of these questions.”
Earlier this year, Makela and his team took two trailers of equipment to Brazil, where researchers will spend the next few years collecting data from the ionosphere. In Brazil, the magnetic equator and geographical equator are at a significant angle, 10 degrees, making this a unique region of the world to study. After the sun goes down at the magnetic equator, plasma bubbles can develop and create instability in the ionosphere. As the bubbles grow, they generate turbulence, which tamper with radio waves used by communications systems.
Makela’s research will focus on how the development of these bubbles is controlled by both the ionosphere and waves generated in the terrestrial atmosphere. To accomplish this, his team has set up two sites about 150 miles apart near the cities of Cariri and Cajazeiras. After collecting data, researchers will synthesize data collected from three types of instruments:
PICASSO imaging system – The Portable Ionospheric Camera and Small-Scale Observatory (PICASSO) boasts custom lenses with a wide field of view that allows the system to capture images from horizon to horizon. It also is able to filter out different emissions, with bright regions indicating greater concentration of electrons and darker regions indicating plasma disturbance. Researchers can clock how fast the dark bands move through the lens, which offer a 1,000 km x 1,000 km view.
Fabry-Pérot interferometer – By studying the details of the spectral emissions created in the ionosphere with the interferometer, researchers can measure Doppler broadening (temperature) and shift (wind) at a 250-km range. This gives a measurement of the properties of atmospheric waves, which may be responsible for the variability in the occurrence of plasma bubbles.
GPS receivers – GPS can pinpoint where radio waves are being disrupted and, by comparing measurements from two closely spaced receivers, the velocity of the structures can be calculated. Comparing velocities measured at the two sites could provide insight into the disturbances and how they develop over time.
“Geospace is so large and complicated that you can’t just take measurements from a single instrument at a single location,” said Makela, who received funding from the Office of Naval Research to purchase equipment for RENOIR. “To understand how everything is interconnected, you need the right instruments at the right locations to make the measurements in an intelligent, coordinated way.”
In addition to his Illinois team, Makela is working with researchers at Clemson University, the Instituto Nacional de Pesquisas Espaciais (INPE), and the Federal University at Campina Grande. RENOIR’s deployment was funded by a NASA grant to Clemson, on which Makela was a co-principal investigator.
The research is part of a larger initiative called SpreadFX, a collaboration led by Colorado Research Associates (CoRA), in which several groups are fielding complementary instruments across Brazil to study this phenomenon in great detail.
“Ultimately, we want to get a better understanding of the conditions in which communication systems are degraded,” he said. “If there is a structure that can’t be mitigated, we need to understand where those structures are so we know where we have usable versus unusable skies.”
For more information about Makela's work, please visit the RENOIR page.