Simulating the effects of scintillation on transionospheric signals with a two‐way phase screen constructed from ALTAIR phase‐derived TEC

Abstract

Severe scintillation on transionospheric radio signals caused by small‐scale plasma irregularities can greatly disrupt wideband communication, surveillance, and navigation systems. Development of techniques to mitigate the effects of scintillation requires accurate characterization of the ionospheric propagation channel. To achieve this goal, multiple campaigns were conducted as part of the joint U.S. ‐UK Wideband Ionospheric Distortion Experiment to obtain ionospheric signatures from various instruments located on Kwajalein Atoll. We use tracking data from the VHF/UHF Advanced Research Project Agency Long‐Range Tracking and Instrumentation Radar for overflights of passive calibration spheres in low‐Earth orbit to demonstrate the validity of a one‐dimensional (1‐D) phase screen model to represent the propagation channel through a disturbed ionosphere. The 1‐D phase screen is constructed from radar phase‐derived estimates of the total electron content. We present a detailed comparison of simulated radar cross section after propagation through the phase screen with observed radar returns under both disturbed and quiet ionospheric conditions. Successful reproduction of radar amplitude enhancements and fades adds to our understanding of small‐scale plasma irregularities and moves us toward our goal of providing precise predictions of radar system performance. Doing so will allow for the development of better mitigation/compensation algorithms for detrimental ionospheric effects. Result from this study also provide an assessment of the tools required for incorporating in situ density measurements along with phase screen theory into situational awareness products to offer an accurate nowcast/forecast of system impacts to users in the communication, navigation, and surveillance communities.

Kalman filter estimation of plasmaspheric total electron content using GPS

“…Second, although we have treated the ALTAIR estimates of TEC as truth data, they are not perfect. Caton et al [2009] estimate that range gate discretization may cause errors in the range‐derived TEC from ALTAIR of up to 1.5 TECU. Third, the equatorial location of ALTAIR is perhaps not the ideal location to carry out this validation.…”

“…We use data collected during ALTAIR tracking scans of passive calibration objects to obtain the TEC along slant lines of sight from the radar to each object. This TEC is computed by differencing the range measurements made at the UHF and VHF frequencies, as described by Caton et al [2009]. When applying this technique to ALTAIR tracking passes of calibration objects in low Earth orbit, the slant TEC measured largely excludes the contribution from the plasmasphere.…”

“…Air Force Research Laboratory also operates an Ashtech Z‐12 GPS receiver on the island of Roi‐Namur (9.40°N, 167.47°E) in close proximity to the ALTAIR radar. Using ALTAIR tracking data from campaigns conducted as part of the joint U.S.‐UK Wideband Ionospheric Distortion Experiment [ Caton et al , 2009; Cannon et al , 2006], we identified a number of angular conjunctions between the calibration objects and the GPS satellites as viewed from Roi‐Namur. Our criterion for identifying the conjunctions is that the angular separation, θ, be 5° or less between the lines of sight to the calibration object and the GPS satellite.…”

Multiple phase screen modeling of ionospheric scintillation along radio occultation raypaths

“…It provides tracking precision metrics, radar cross section (RCS) signature, and range-Doppler imaging for deep-space operations, satellite observations, strategic reentry missions, and multiple-intercept engagement tracking. Situated at 4.3°N magnetic dip latitude, the radar is also well suited for investigations of incoherent and coherent backscatter from the equatorial ionosphere [e.g., Caton et al, 2009;Hysell et al, 2006;Tsunoda et al, 1979]. The fully steerable parabolic dish antenna (46 m diameter) operates in dualfrequency mode transmitting signals at 158 MHz (VHF) and 422 MHz (UHF).…”

“…[19] The SCINDA network of ionospheric monitoring instruments is maintained by Air Force Research Laboratory and includes VHF and GPS scintillation receivers colocated with the ALTAIR radar on the island of Roi-Naumr [Groves et al, 1997;Caton et al, 2009]. The 244 MHz signal broadcasted by a geostationary communications satellite were monitored using spaced antennas and cross-correlated to obtain the zonal drift velocity on 21 April 2009 (Figure 7).…”