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KILOMETER-SPACED GNSS ARRAY FOR IONOSPHERIC IRREGULARITY MONITORING
Title
KILOMETER-SPACED GNSS ARRAY FOR IONOSPHERIC IRREGULARITY MONITORING
Creator
Su, Yang
Date
2017, 2017-05
Description
This dissertation presents automated, systematic data collection, processing, and analysis methods for studying the spatial-temporal...
Show moreThis dissertation presents automated, systematic data collection, processing, and analysis methods for studying the spatial-temporal properties of Global Navigation Satellite Systems (GNSS) scintillations produced by ionospheric irregularities at high latitudes using a closely spaced multi-receiver array deployed in the northern auroral zone. The main contributions include 1) automated scintillation monitoring, 2) estimation of drift and anisotropy of the irregularities, 3) error analysis of the drift estimates, and 4) multi-instrument study of the ionosphere. A radiowave propagating through the ionosphere, consisting of ionized plasma, may su↵er from rapid signal amplitude and/or phase fluctuations known as scintillation. Caused by non-uniform structures in the ionosphere, intense scintillation can lead to GNSS navigation and high-frequency (HF) communication failures. With specialized GNSS receivers, scintillation can be studied to better understand the structure and dynamics of the ionospheric irregularities, which can be parameterized by altitude, drift motion, anisotropy of the shape, horizontal spatial extent and their time evolution. To study the structuring and motion of ionospheric irregularities at the sub-kilometer scale sizes that produce L-band scintillations, a closely-spaced GNSS array has been established in the auroral zone at Poker Flat Research Range, Alaska to investigate high latitude scintillation and irregularities. Routinely collecting lowrate scintillation statistics, the array database also provides 100 Hz power and phase data for each channel at L1/L2C frequency. In this work, a survey of seasonal and hourly dependence of L1 scintillation events over the course of a year is discussed. To efficiently and systematically study scintillation events, an automated low-rate scintillation detection routine is established and performed for each day by screening the phase scintillation index. The spaced-receiver technique is applied to cross-correlated phase and power measurements from GNSS receivers. Results of horizontal drift velocities and anisotropy ellipses derived from the parameters are shown for several detected events. Results show the possibility of routinely quantifying ionospheric irregularities by drifts and anisotropy. Error analysis on estimated properties is performed to further evaluate the estimation quality. Uncertainties are quantified by ensemble simulation of noise on the phase signals carried through to the observations of the spaced-receiver linear system. These covariances are then propagated through to uncertainties on drifts. A case study of a single scintillating satellite observed by the array is used to demonstrate the uncertainty estimation process. The distributed array is used in coordination with other measuring techniques such as incoherent scatter radar and optical all-sky imagers. These scintillations are correlated with auroral activity, based on all-sky camera images. Measurements and uncertainty estimates made over a 30-minute period are made and compared to a collocated incoherent scatter radar, and show good agreement in horizontal drift speed and direction during periods of scintillation for cases when the characteristic velocity is less than the drift velocity. The methods demonstrated are extensible to other zones and other GNSS arrays of varying size, number, ground distribution, and transmitter frequency.
Ph.D. in Mechanical and Aerospace Engineeering, May 2017
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IDENTIFYING E AND F LAYER IONOSPHERIC IRREGULARITIES WITH A SCINTILLATION AURORAL GPS ARRAY
Title
IDENTIFYING E AND F LAYER IONOSPHERIC IRREGULARITIES WITH A SCINTILLATION AURORAL GPS ARRAY
Creator
Sreenivash, Vaishnavi
Date
2018, 2018-05
Description
The Scintillation Auroral GPS Array (SAGA), comprising six kilometer-spaced receivers located in Poker Flat, Alaska, has been deployed for...
Show moreThe Scintillation Auroral GPS Array (SAGA), comprising six kilometer-spaced receivers located in Poker Flat, Alaska, has been deployed for four years to study high latitude scintillation effects on L1 and L2C frequency Global Positioning System (GPS) signals. These scintillations disrupt the GPS signals received on the earth, affecting navigation services. Scintillation is associated with the variations in plasma densities known as irregularities, present in the ionosphere. Research on scintillation has been done from the past using different instruments and techniques, and for multiple purposes. One important prior effort is automated detection of the scintillation of L1 frequency GPS signals. Other successful research includes estimating the drift velocity of irregularities, anisotropy, height and thickness of the scattering layer. It is important to check before studying the properties of irregularities whether the sensors can detect the scintillations happening in the E or F region. In other words, it is essential to check that the sensors are sensitive not only to F region scintillations but also to the E region scintillations. The purpose of this work is to identify the ionospheric region, E or F, which is responsible for the scintillation on the L1 and L2C GPS signals. The scintillations of these GPS signals are further classified based on the type of scintillation i.e., phase scintillation and amplitude scintillation. The scintillation events are categorized as amplitude, phase, or both on L1 or L2C frequency occurring in the E or F region. Using the automated scintillation detection routine, a complete list of phase and amplitude scintillations on all days for both the frequencies L1/L2C in the years 2014 and 2015 is created. The highly scintillating days for 2014 and 2015 are sorted and the irregularities layer associated with these scintillation events are identified. The Poker Flat Incoherent Scatter Radar (PFISR) and All Sky Camera images are used to develop the process of identifying the ionospheric region. The electron density from PFISR is assumed to be an essential parameter to determine the E/F layer irregularities. The All Sky Camera provides the red auroral brightness and the green auroral brightness, where red aurora implies F region and the green aurora implies E region. A summary of a subset of the scintillation events occurring on the highly scintillating days in 2014 and 2015 is provided through this work. It is found that phase scintillation is occurring more predominantly in the high latitudes than the amplitude scintillation. A number of these are attributed to E and F region irregularities. In future, the scintillation events obtained from this work will be used to study the E and F layers irregularities and properties in detail.
M.S. in Mechanical and Aerospace Engineering, May 2018
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