Automated Ionospheric Scattering Layer Hypothesis Generation for Detected and Classified Auroral Global Positioning System Scintillation Events

Abstract

We describe a method to detect and classify global positioning system (GPS) scintillation, and then hypothesize a possible ionospheric layer scattering the signal. The objective is to routinely identify events of interest to investigate in detail in future work. Scintillation types include amplitude, phase, or both amplitude and phase. A scintillation event is one for which a scintillation index remains above a threshold across a majority of closely spaced receivers viewing a single satellite. Events are categorized by signal frequency and scintillation type. An event is then hypothesized to be due to the E or F layer using an independent data source. Data from the scintillation auroral GPS array located in Poker Flat Research Range, Alaska, are used to analyze L1 and L2C frequencies in 2014 and 2015. The irregularity layer associated with each scintillation event is hypothesized to be due to the activity in the E layer of the ionosphere (below 150 km) or in the F layer (above 195 km) using collocated Poker Flat Incoherent Scatter Radar electron density measurements. Events in a transition layer (150-195 km) and inconclusive results are also recorded. We find that nearly all of the over 4,000 events are phase scintillations. The majority of the events are hypothesized to occur when the peak density is at E-layer altitudes. This indicates that E-layer-related scintillation may be quite common at auroral latitudes and that GPS receivers are sensitive to the irregularities occurring both there and at F layer altitudes.Plain Language Summary As global positioning system (GPS) signals pass through Earth's atmosphere, they may "twinkle" when received at the ground due to variations in the number of charged particles present in the ionized layer of the Earth's atmosphere, the ionosphere. The twinkling or rapid fluctuation in the GPS signals is called ionospheric scintillation. We develop a way, using data from GPS receivers and a nearby radar, to detect and classify scintillations measured in Alaska in 2014 and 2015, and then make an educated guess about whether they are in the upper or lower layer of the ionosphere. This method will be useful for handling large data sets of scintillation, which are now becoming more common. We find that, even though most of the ionosphere's charged particles are usually above 195 km height, GPS is sensitive to scintillations at high latitudes due to variations in a lower layer below 150 km, and these happen a majority of the time.

Multiyear Detection, Classification and Hypothesis of Ionospheric Layer Causing GNSS Scintillation

“…A scintillation receiver or array is required for detection and classification of scintillation types and time intervals. A collocated measure of electron density is needed for hypothesizing the layer in the manner described by Sreenivash et al (2020). As in that work, we use the Scintillation Auroral GPS Array (SAGA) for measuring scintillation and the Poker Flat Incoherent Scatter Radar (PFISR) for electron density measurements.…”

“…In the auroral zone, scintillations have been observed to be associated with auroral arcs, which may arise in the E layer or the F layer (Mrak et al, 2018). Recently a method of hypothesizing an irregularity layer based on incoherent scatter radar measurements of peak density was introduced to survey high-latitude phase scintillations observed from a closely spaced array of scintillation receivers during the years 2014-2015 (Sreenivash et al, 2020). For those solar maximum years, for the incoherent scatter radar processed and available at that time, E layer and F layer phase scintillations were both common.…”

Ionospheric Irregularity Layer Height and Thickness Estimation With a GNSS Receiver Array

“…SAGA consists of up to seven connected autonomous space environment sensors (CASES) scintillation receivers sited at baseline distances ranging from about 200 m to 3 km apart [12]. An arraywide interval of scintillation received from GPS satellite PRN 23 at L1 was detected from about 03:43-04:17 UT using scintillation indices [13], [27]. These 100-Hz measurements are then processed for the time periods identified by techniques detailed in [28] to obtain detrended and filtered high-rate amplitude/phase observations.…”

“…The limit on thickness enforces that the scattering layer does not extend all the way to the ground but must end at the bottom of the ionosphere in order to remain physically realistic. We select the best fit spectrum as the one that minimizes the mean-squared error in (27) between the observed and measured ratios. Considering that the Rytov approximation tends to be smoother than the actual signal spectra [15], the meansquared errors 2 are computed for the portion of the spectral ratios between κ v corresponding to the minimum value of the ratio and κ v three times larger than the lowest wavenumber at which the ratio exceeds 1.…”

“…8(c). As in [27] PFISR long pulse measurements are plotted above 195 km and alternating code measurements are plotted below 195 km altitude. The color indicates an F region density enhancement; temperatures are enhanced during this period as well (not shown), attributed to energetic particle precipitation [12].…”