A Novel Approach for Monitoring Zonal Irregularity Drift Using a Stand-Alone GNSS Scintillation Monitor

Charles S. Carrano, Keith M. Groves, Susan H. Delay, Patricia H. Doherty

Peer Reviewed

Abstract:	A complete characterization of field-aligned ionospheric irregularities responsible for the scintillation of GNSS satellite signals includes not only their spectral properties (power spectral strength, spectral index, outer-scale, and anisotropy) but also their bulk motion, or drift. At low latitudes, the irregularity drift is predominantly zonal and controlled by the F region dynamo and regional electrodynamics. These physical processes are of considerable interest and are currently investigated using a variety of measurement techniques. From a system impacts perspective, the irregularity drift is important because it affects the rate of signal fading and the level of phase fluctuations encountered by the receiver (both of which influence its ability to maintain lock on the satellite signals). The zonal irregularity drift is most commonly measured at low-latitudes by cross-correlating observations of a satellite signal made by a pair of closely-spaced receivers. The AFRL-SCINDA network operates a small number of VHF spaced-receiver systems at low latitude stations for this purpose. A far greater number of GNSS scintillation monitors are operated by AFRL-SCINDA (25-30) and the Low Latitude Ionospheric Sensor Network (35-50), but the individual receivers are too widely separated to monitor the drift using cross-correlation techniques. Previous authors have attempted to measure the drift using a single GNSS receiver by cross-correlating the signals from different satellites, but differences in the satellite scan directions with respect to the field-aligned irregularities tend to degrade the correlation (thereby limiting the usefulness of this technique). In this paper, we present an alternative approach that leverages the weak scatter scintillation theory [Rino, Radio Sci., 1979] to infer the zonal irregularity drift from single-station GNSS measurements of S4, ??, and the propagation geometry alone. Unlike the spaced-receiver technique, this approach requires assumptions regarding the height of the scattering layer (which introduces a bias in the drift estimates) and the spectral index of the irregularities (which affects the spread of the drift estimates about the mean). Nevertheless, theory and experiment show that the ratio of ?? to S4 is less sensitive to these parameters than it is to the zonal drift. We validate the technique using VHF spacer-receiver measurements of zonal irregularity drift obtained from the AFRL-SCINDA network. We believe this work may have important ramifications for the high-latitude ionospheric community, who commonly observe phase without amplitude scintillations at high latitudes and therefore tend to study S4 and ?? as if they were independent. Our results demonstrate that S4 and ?? are closely related, with their ratio depending on the irregularity drift and propagation geometry more strongly than the structure of the irregularities or the geophysical processes by which they were created. While the spaced receiver technique remains the preferred way to monitor the irregularity drift when closely pairs of receivers are available, our technique enables a new opportunity to monitor zonal irregularity drift using regional or global networks of widely separated GNSS scintillation monitors.
Published in:	Proceedings of the 2015 International Technical Meeting of The Institute of Navigation January 26 - 28, 2015 Laguna Cliffs Marriott Dana Point, California
Pages:	530 - 544
Cite this article:	Carrano, Charles S., Groves, Keith M., Delay, Susan H., Doherty, Patricia H., "A Novel Approach for Monitoring Zonal Irregularity Drift Using a Stand-Alone GNSS Scintillation Monitor," Proceedings of the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, California, January 2015, pp. 530-544.
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