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Satellite's instrumentation providing scintillation forecast data

by Michael Kleiman
377th Air Base Wing Public Affairs

7/10/2008 - KIRTLAND AIR FORCE BASE, N.M. (AFPN) -- Whether it's static interrupting a radio station, or crackling noises interfering with a theater commander's attempt to contact a deployed unit, scintillation can cause communication chaos.

Scintillation occasionally occurs when radio waves transiting an unstable ionosphere, located 50 to 360 miles above the Earth, become deformed, fragile, or misplaced. This results in transmission difficulties for communication or global positioning system satellites. Ultimately, it hampers warfighters' effectiveness.

Scientists examining the ionospheric aberrations discovered these aberrations happen more closely in the equatorial and auroral areas between twilight and midnight. There are also seasonal fluctuations and a long-term variation corresponding to the solar cycle.

Within the Air Force, a six-instrument payload onboard the Communication/Navigation Outage Forecasting System spacecraft is helping researchers forecast when and where this natural phenomenon will occur.

"This is the first mission by any organization dedicated to ionospheric scintillation," said Dr. Laila Jeong, Air Force Research Laboratory program manager for C/NOFS. "We're going to collect a stellar database of ionospheric data."

During the initial month of the C/NOFS flight -- which began its 13-month mission in April -- program people evaluated the instrumentation suite to ensure expected performance. Since then, the payload package has functioned properly in responding to sent commands and tasks.

The six sensors installed on the satellite to monitor scintillation, along with their function, are:

-- Planar langmuir probe: calculates the amount of charged particles in the satellite's course. When the material strikes the metal plate on the front of the device, they generate an electric signal, which if fluctuating, could indicate scintillation. Collected data can be employed in models to identify exactly where the ionospheric disturbances occurred during the computation and when they might transpire in the future. AFRL's Space Vehicles Directorate constructed the probe.

-- Ion velocity meter: measures charged particles' speed and direction, perpendicular to and in the same path, of the satellite's orbital movement in a particular region of the ionosphere. Built by the University of Texas at Dallas, information compiled by the system contributes to physics software designed by the Space Vehicles Directorate to forecast scintillation.

-- Neutral wind meter: computes the pace and track of the gas (uncharged particles) travelling in the spacecraft's route and in a vertical course to C/NOFS' movement in the ionosphere. This device was built by the University of Texas at Dallas.

-- Vector electric field instrument: gauges the existing force in a region between opposite-charged particles. This amount is referred to as the electric field and the instrument's payload computes the power and direction of it. Over time, changes in the electric field serve as an indicator of upcoming scintillation. NASA's Goddard Space Flight Center in Greenbelt, Md., built the instrument.

-- Coherent electromagnetic radio tomography: evaluates the signals calculated by ground receivers to verify the quantity of scintillation along the course between the C/NOFS spacecraft and the planet's surface. If the signals display distortion, scintillation is evident and vice versa. The U.S. Naval Research Laboratory's system contains a beacon and antenna transmitting on three frequencies to Earth.

-- C/NOFS occultation receiver for ionospheric sensing and specification: measures signals originating from numerous global positioning system satellites orbiting the globe. The system examines these signals to determine the extent of charged matter between the GPS spacecraft and C/NOFS. The Aerospace Corp.-constructed payload features a specially-developed GPS receiver and antenna for remote sensing.

"Data collected by the six instruments is sent to a processing center at the Space Vehicles Directorate's Battlespace Environment Division at Hanscom Air Force Base, Massachusetts, where project staff run forecasting models and create forecast products," Dr. Jeong explained. "The information is made available to the scientific and military user community, and the program will continue to provide scintillation data as long as the C/NOFS satellite remains in orbit -- it has a predicted lifetime of three to four years.

"The analysis done on the information compiled by the six instruments will pave the way for the next generation of scintillation forecasting models -- improving upon the accuracy of forecasting and extending the forecasting time period further into the future," Dr. Jeong said. "The benefits of the collected data from C/NOFS will ultimately impact the warfighter through improved communication and greater operational efficiency."

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