Satellite instruments provide landmark forecast data Published July 18, 2008 By Michael P. Kleiman 377th Air Base Wing public affairs KIRTLAND AIR FORCE BASE, New Mexico -- Imagine trying to listen to your favorite radio station, but steady static interrupts the broadcast. Likewise, an in-theater commander attempts to establish contact with one of his deployed units poised for an important operation and cannot due to constant crackling noise - mission improbable! Blame the communication chaos on scintillation, which occasionally occurs when radio waves transiting an unstable ionosphere, located 50 to 360 miles above the Earth, become deformed, fragile or misplaced. This causes significant transmission difficulties for communication or global positioning system satellites and ultimately hampers the warfighter's effectiveness. Scientists examining the ionospheric aberrations have discovered they happen more closely in the equatorial and auroral areas between twilight and midnight. They also experience seasonal fluctuations and a long-term variation corresponding to the solar cycle. Forecasting when and where this natural phenomenon transpires has been enhanced with the six-instrument payload onboard the Communication/Navigation Outage Forecasting System spacecraft, which began its 13-month mission on April 16. "This is the first mission by any organization dedicated to ionospheric scintillation. We're going to collect a stellar database of ionospheric data," said Dr. Laila Jeong, Air Force Research Laboratory program manager for C/NOFS, AFRL's Space Vehicles Directorate. During the initial month of the C/NOFS flight, program personnel evaluated the instrumentation suite to ensure expected performance and since then, the payload package has functioned properly in responding to sent commands and tasks. Six sensors are installed on the satellite to monitor scintillation: Planar Langmuir Probe Constructed by the Space Vehicles Directorate, the 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. This process is known as forecasting. Ion Velocity Meter Comprises two sensors, the 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. Information compiled by the system built by the University of Texas at Dallas contributes to physics software designed by the Space Vehicles Directorate to forecast scintillation. Neutral Wind Meter Another instrument containing a couple of information-gathering mechanisms and made by the University of Texas at Dallas is the Neutral Wind Meter. It computes the pace and track of the gas (uncharged particles) travelling in the spacecraft's route and in a vertical course to CNOFS' movement in the ionosphere. Compiled data provides inputs for scintillation prediction models. Vector Electric Field Instrument Built by the National Aeronautics and Space Administration's Goddard Space Flight Center, Greenbelt, Md., the Vector Electric Field Instrument, comprised of six booms measuring 33 feet in length each with a sensor positioned on the tip, gauges the existing force in a region between opposite-charged particles. This amount is referred to as the electric field and the VEFI payload computes the power and direction of it. Over time, changes in the electric field serve as an indicator of upcoming scintillation. Collected information supports ionosphere disturbance forecasting models. Coherent Electromagnetic Radio Tomography Containing a beacon and antenna transmitting on three frequencies to the Earth, the U.S. Naval Research Laboratory's 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. Data supplied by CERTO assists in foretelling when scintillation could occur. C/NOFS Occultation Receiver for Ionospheric Sensing and Specification Finally, the C/NOFS Occultation Receiver for Ionospheric Sensing and Specification features a specially-developed GPS receiver and antenna for remote sensing. The Aerospace Corp.-constructed payload measures signals originating from numerous GPS satellites orbiting the globe. CORISS examines these signals to determine the extent of charged matter between the GPS spacecraft and C/NOFS. Like the other five instruments, information obtained from CORISS helps in formulating scintillation forecast representations. "Data collected by the six instruments is sent to a processing center at the Space Vehicles Directorate's Battlespace Environment Division at Hanscom AFB, Mass., where project staff run forecasting models and create forecast products," said Dr. Jeong. "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." A collaboration between the Space Vehicles Directorate and the Space and Missile Systems Center's Space Development and Test Wing also located at Kirtland AFB, C/NOFS' mission has also received significant support from NASA regarding transmission of scintillation data. For example, C/NOFS sends the near real-time information to a NASA satellite, which in turn, downloads the data to the processing site at Hanscom AFB. "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," said Dr. Jeong. "The benefits of the collected data from C/NOFS will ultimately impact the warfighter through improved communication and greater operational efficiency."