694014 event 1794418992 1794419010 <![CDATA[Ph.D. Dissertation Defense - Evan Worthington]]> Title:  D-region Characterization With Trans-ionospheric VLF Signals

Committee:

Dr. Morris Cohen, ECE, Chair, Advisor

Dr. Bharat Kunduri, ECE

Dr. Paul Steffes, ECE

Dr. Andrew Peterson, ECE

Dr. Glenn Lightsey, AE

Dr. Michael Peterson, GTRI-SEAL

]]> Very low frequency (VLF, 3–30 kHz) signals, emitted by either manmade or natural sources, travel long distances in sub-ionospheric propagation modes. Some of this energy couples into the ionosphere and travels to satellite altitudes along a predominantly field-aligned path in what is known as a “whistler” propagation mode. Along this path, these VLF signals encounter both frequency-dependent absorption and dispersion. When observed by satellites, these signals can be used to estimate the electron densities along the path to the satellite. New techniques for estimating electron densities in the lower ionosphere are presented using trans-ionospheric VLF signals recorded by the DEMETER satellite. These techniques employ an inverse modeling-based approach to select a parameterized model of electron densities in the D-region (60–90 km). Leveraging both narrowband and wideband field measurements recorded by DEMETER over the course of its six-year mission, the algorithms presented produce estimates of D-region electron densities that are consistent with expected values and represent new tools for the study of the lower ionosphere, a region that has proven challenging to study with traditional sensing methods.

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