Mathematics – Logic
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsa52a..08c&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SA52A-08
Mathematics
Logic
2407 Auroral Ionosphere (2704), 7944 Ionospheric Effects On Radio Waves
Scientific paper
The Space-Based Radar Ionospheric Effects Simulation (SBR-IES) tool was developed to predict the degrading effects of the ionosphere on the performance of space-based radar systems. This presentation focuses on the technique used by the SBR-IES to predict radar electrojet clutter. The term electrojet clutter refers to backscatter from electron density irregularities that develop in response to unstable (two-stream) current systems in the auroral and equatorial electrojets. The two-stream instability is a dominant mechanism for the generation of electrojet clutter for radars operating in and above the VHF frequency band. The effects of these irregularities on the performance of ground- and space-based radars are discussed. The ionospheric clutter predictions are made using the approach developed for the Comprehensive E-Region Auroral Clutter (CERAC) model by SRI International and Rome Laboratory. The threshold velocity required for the generation of ionospheric irregularities by the two-stream instability is computed using nonlinear plasma wave theory. The streaming velocity, or the relative velocity between the electrons and ions, is calculated based on the ExB drift. When the streaming velocity exceeds the threshold, the clutter strength is estimated using an empirical relationship involving the radar frequency, electron density, magnetic aspect angle, and flow angle. A uniformly distributed layer of scattering irregularities is assumed. The ionospheric clutter predictions provided by the initial version of the SBR-IES tool were based on a climatological, or average, description of ionospheric conditions at the time of observation, driven by Kp, Ap, and the 10.7 cm solar flux. This approach, while having the advantage of requiring only a few geophysical input parameters to run, is limited by the use of overly simplified (smoothed) climatological models for the electric field, as well as electron, ion, and neutral densities and temperatures within the E-region. This deficiency is particularly pronounced during geomagnetic storm activity, when the ionospheric response deviates most from climatological behavior. The latest version of the SBR-IES tool can accept, as input, real-time specifications of the ionosphere provided by global assimilative models (e.g. PRISM or GAIM) that are currently or soon to be in operational use at AFWA. Forecasts of radar clutter can be generated using forecasts of the ionospheric state provided by the Ionospheric Forecast Model (IFM), for example. In the near future we plan to include the high resolution specification of the electric field provided by the real-time incoherent scatter radars of the Super Dual Auroral Radar Network (SuperDARN). It is expected that the use of data assimilative models to provide the background ionospheric densities, temperatures, and electric field will lead to substantially more accurate and high resolution predictions of radar electrojet clutter. Moreover, these improvements can be made without sacrificing real-time impact assessment requirements.
Alcala C. M.
Carrano Charles S.
Daniell Robert E.
Donatelli Delia E.
Groves Keith M.
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