Date of Award


Document Type


Degree Name

Master of Science in Applied Physics


Department of Engineering Physics

First Advisor

Christopher G. Smithtro, PhD


An assessment of the impact of various ionospheric models on high-frequency (HF) signal raytracing is presented. Ionospheric refraction can strongly affect the propagation of HF signals. Consequently, Department of Defense missions such as over-the-horizon RADAR, HF communications, and geo-location all depend on an accurate specification of the ionosphere. Five case studies explore ionospheric conditions ranging from quiet conditions to solar flares and geomagnetic storms. It is shown that an E layer by itself can increase an HF signal’s ground range by over 100 km, stressing the importance of accurately specifying the lower ionosphere. It is also shown that the GPSII model has the potential to capture the expected daily variability of the ionosphere by using Total Electron Content data. This daily variability can change an HF signal’s ground range by as much as 5 km per day. The upper-ionospheric response to both a solar flare and a geomagnetic storm is captured by the GPSII model. In contrast, the GPSII model does not capture the lower-ionospheric response to either event. These results suggest that using the GPSII model’s passive technique by itself may only be beneficial to specifying the ionosphere above the E region, especially during solar flares and geomagnetic storms.

AFIT Designator


DTIC Accession Number