@proceedings {859, title = {Estimation of Ionospheric Layer Height by Measuring the Time Difference of Arrival (TDOA) Between 1 and 2 Hop Propagation Modes. 2023 Annular Eclipse Observations}, year = {2024}, month = {03/2024}, publisher = {HamSCI}, address = {Cleveland, OH}, abstract = {

A HamSCI science objective for the 2023 and 2024 eclipses is to use amateur radio stations to measure how the ionosphere changes with eclipse passage. Of particular interest is the change in effective ionization layer height caused by the momentary blockage of solar radiation. Layer height between two stations can be deduced from a Time of Flight (TOF) measurement but doing so requires complexity beyond the capability of most amateur radio stations. Particularly difficult requirements are precision absolute time references for both stations and calibration of the lengthy time delays incurred in modern DSP based transceivers. A simpler method that can be just as effective is to measure the Time Difference of Arrival (TDOA) between the 1- and 2- hop modes over paths and frequencies that support both modes. The 1-hop mode is shorter and arrives first, followed by the longer 2-hop mode. Geometric models based on virtual height or refractive ray tracing can be used to mathematically relate 1-2 hop TDOA to layer height. The measurement can be implemented by transmitting audio signals that are sensitive to a time delay when summed together, as happens in the receiver during simultaneous 1 and 2 hop propagation. Suitable audio waveforms include a 1-cycle audio burst, audio chirps of controlled sweep rate, and a pseudorandom noise burst. The TDOA measurement using the short pulses is performed by directly measuring the time difference between the two received pulses. The summation of a chirp waveform with a delayed copy of itself produces a beat note equal to the product of the sweep rate and the time delay that can be used to calculate TDOA. The TDOA can be extracted from both the PN bursts and chirps through an autocorrelation technique. The audio signals can simply be fed to the microphone input and recovered from the speaker output of ordinary SSB amateur radio equipment using audio .wav programs. This paper gives details of the method and of on-air experiments both before and during the 2023 Annular Eclipse.

}, author = {Steven A. Cerwin and Paul Bilberry and Sam Blackshear and Jesse T. McMahan and Kristina V. Collins and Nathaniel A. Frissell} } @proceedings {834, title = {Extreme Values in Short-Term 20 m Sequential Matched WSPR Observations}, year = {2024}, month = {03/2024}, publisher = {HamSCI}, address = {Cleveland, OH}, abstract = {

Automated amateur radio networks, such as WSPRnet, daily compile data on hundreds of millions of radio contacts. This wealth of information is valuable for researchers exploring and forecasting High-Frequency (HF) propagation and its correlation with solar phenomena. A prerequisite for meaningful investigations is a comprehensive understanding and documentation of the inherent variability present in the data. Prior investigations highlighted the extreme short-term variability in SNR reports from 20-meter sequential matched observations, variability in excess of usual distributional assumptions.\  Here, we describe and model those extreme observations.\  Using descriptive statistics and logistic regressions, we provide evidence of some temporal and spatial patterns associated with the extreme SNR values and develop predictions for their occurrence.

}, author = {Robert B. Gerzoff and Nathaniel A. Frissell} } @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 = {

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.\  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\  height profile derived from Doppler data and data from ray trace programs and ionosonde measurements are given.

}, author = {Steven Cerwin and Kristina V. Collins and Dev Joshi and Nathaniel A. Frissell} } @conference {51, title = {e-POP Radio Science Using Amateur Radio Transmissions}, booktitle = {Fall AGU - Poster Presentation}, year = {2015}, month = {12/2015}, publisher = {American Geophysical Union}, organization = {American Geophysical Union}, address = {San Francisco, CA}, abstract = {

A major component of the enhanced Polar Outflow Probe (e-POP) Radio Receiver Instrument (RRI) mission is to utilize artificially generated radio emissions to study High Frequency (HF) radio wave propagation in the ionosphere. In the North American and European sectors, communications between amateur radio operators are a persistent and abundant source source of HF transmissions. We present the results of HF radio wave propagation experiments using amateur radio transmissions as an HF source for e-POP RRI. We detail how a distributed and autonomously operated amateur radio network can be leveraged to study HF radio wave propagation as well as the structuring and dynamics of the ionosphere over a large geographic region. In one case, the sudden disappearance of nearly two-dozen amateur radio HF sources located in the midwestern United States was used to detect a enhancement in foF2 in that same region. We compare our results to those from other more conventional radio instruments and models of the ionosphere to demonstrate the scientific merit of incorporating amateur radio networks for radio science at HF.

}, author = {Nathaniel A. Frissell and Gareth Perry and Ethan S. Miller and Alex Shovkoplyas and Magdalina Moses and H. James and Andrew Yau} }