@proceedings {459,
	title = {Estimation of Ionospheric Layer Height Changes From Doppler Frequency and Time of Flight Measurements on HF Skywave Signals},
	year = {2021},
	month = {03/2021},
	publisher = {HamSCI},
	address = {Scranton, PA (Virtual)},
	abstract = {<p>The HamSCI community has been studying apparent frequency shifts in the reception of HF skywave signals from radio station WWV in Ft. Collins, CO. WWV is a standard time and frequency station with atomic clock accuracy. If the receiving station uses a GPS Disciplined Oscillator (GPSDO) for a frequency reference, the atomic clock accuracy on both ends guarantees any observed frequency shifts are attributable only to propagation effects through the ionosphere. Causes for frequency shifts in the received signal are recognized as complex and varied. A leading candidate is Doppler shift resulting from dynamic changes in refraction layer height. These, in turn, are caused by the diurnal transitions between night and day, passage of an eclipse shadow, and ionospheric disturbances originating from solar flares or X-ray events. For the case of changing refraction layer height, an analysis of Doppler frequency and Time of Flight (TOF) data can estimate the changes in skywave path length between the transmitter and receiver.\&nbsp; This data can be used in conjunction with an assumed geometric model and propagation mode to infer the corresponding height profile over time. This paper postulates one possible mechanism for observed frequency swings and presents supporting experimental evidence. Comparisons between the calculated\&nbsp; height profile derived from Doppler data and data from ray trace programs and ionosonde measurements are given.</p>
},
	author = {Steven Cerwin and Kristina V. Collins and Dev Joshi and Nathaniel A. Frissell}
}
@conference {540,
	title = {HamSCI Personal Space Weather Station (PSWS): Architecture and Current Status},
	booktitle = {NSF CEDAR (Coupling, Energetics, and Dynamics of Atmospheric Regions)},
	year = {2021},
	month = {06/2021},
	publisher = {CEDAR},
	organization = {CEDAR},
	address = {Virtual},
	abstract = {<p>Recent advances in geospace remote sensing have shown that large-scale distributed networks of ground-based sensors pay large dividends by providing a big picture view of phenomena that were previously observed only by point-measurements. While existing instrument networks provide excellent insight into ionospheric and space science, the system remains undersampled and more observations are needed to advance understanding. In an effort to generate these additional measurements, the Ham Radio Science Citizen Investigation (HamSCI, hamsci.org) is working with the Tucson Amateur Packet Radio Corporation (TAPR, tapr.org), an engineering organization comprised of volunteer amateur radio operators and engineers, to develop a network of Personal Space Weather Stations (PSWS). These instruments that will provide scientific-grade observations of signals-of-opportunity across the HF bands from volunteer citizen observers as part of the NSF Distributed Array of Small Instruments (DASI) program. A performance-driven PSWS design (~US$500) will be a modular, multi-instrument device that will consist of a dual-channel phase-locked 0.1-60 MHz software defined radio (SDR) receiver, a ground magnetometer with (~10 nT resolution and 1-sec cadence), and GPS/GNSS receiver to provide precision time stamping and serve as a GPS disciplined oscillator (GPSDO) to provide stability to the SDR receiver. A low-cost PSWS (\&lt; US$100) that measures Doppler shift of HF signals received from standards stations such as WWV (US) and CHU (Canada) and includes a magnetometer is also being developed. HF sounding algorithms making use of signals of opportunity will be developed for the SDR-based PSWS. All measurements will be collected into a central database for coordinated analysis and made available for public access.</p>
},
	author = {Nathaniel A. Frissell and Dev Joshi and Veronica I. Romanek and Kristina V. Collins and Aidan Montare and David Kazdan and John Gibbons and William D. Engelke and Travis Atkison and Hyomin Kim and Scott H. Cowling and Thomas C. McDermott and John Ackermann and David Witten and Julius Madey and H. Ward Silver and William Liles and Steven Cerwin and Philip J. Erickson and Ethan S. Miller and Juha Vierinen}
}
