GNSS ionospheric scintillation studies in Singapore

• Main Author: Dhimas Sentanu Murti
• Other Authors: Tan Eng Leong
• Format: Theses and Dissertations
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Satellite telecommunication; DRNTU::Science::Physics::Geophysics and geomagnetism; DRNTU::Engineering::Electrical and electronic engineering::Wireless communication systems
• Online Access: https://hdl.handle.net/10356/65415
• Institution: Nanyang Technological University

Ionospheric scintillation has been a challenge for Global Navigation Satellites System (GNSS) application especially in equatorial region. Ionosphere in around equatorial region is known to have unique characteristic. The existence of horizontal geomagnetic field and eastward electric field in this region caused equatorial ionosphere anomaly (EIA) effect, which subsequently inflicts high ionospheric activity. Singapore is located around equatorial region, which makes it an interesting place to perform research about ionospheric scintillation. Moreover year 2012-2014 is the year of high solar activity which implies higher ionosphere activity. Being susceptible to such adverse effects, GNSS which is free and continuously available can be used as ionospheric scintillation monitoring tool. This thesis presents the analysis and studies of ionospheric scintillation in Singapore. Monthly S4 mean obtained from Global Positioning System (GPS) signal during year 2013 is presented. This analysis shows that high ionospheric scintillation happens during equinox months which are around April and September. This behavior is attributed to the close alignment of the solar terminator with magnetic meridian. Ionospheric scintillation happens mostly at night between 8pm to 12am. This is due to plasma bubble irregularities caused by E x B vertical force. E is earth electric filed and B is magnetic field. Selected GPS scintillation events during the equinox months are presented by various scintillation parameters. Increased value of S4 (amplitude scintillation), phi60 (phase scintillation), and ROTI (rate of change of total electron content index) are shown to occur concurrently. This indicates that both signal intensity and the carrier phase of the GPS signal exhibit fluctuations while propagating through the plasma bubble irregularities of the ionosphere layer during this period. Sunspot number and solar flux are also analyzed as indicators of solar activity. Results show that in long term, during years 2009-2013, high solar activity is a factor that increases ionospheric scintillation possibility. Geomagnetic disturbance is also observed which shows that ionospheric scintillation is inhibited during geomagnetic disturbed days. Next, the correlations of various ionospheric scintillation parameters between receivers at S2, S2.1, and Nanyang House building in Nanyang Technological University (NTU) are calculated. These three receivers are separated by furthest distance of 1 km of each other. The correlation coefficients obtained are found to be nearly one which means that the bubble irregularities do not have significant difference in one km distance. Then, cross correlation of signal intensity between those locations are calculated to show that plasma irregularities drift toward eastward direction. Spatial distribution of scintillation is presented by sky plot which shows that scintillations are more concentrated in the south part of Singapore where the peak of Equatorial Ionization Anomaly (EIA) is located. The study of the effect of scintillation on positioning accuracy is also done. The pseudorange fluctuation is found to be proportional to S4 and phi60. Next, ionospheric scintillation analysis using GLONASS and BeiDou which are the satellite navigation system owned by Russia and China respectively are presented as comparison. They show consistent results as those obtained by GPS with exception on the phi60 by GLONASS and total electron content (TEC) by both GLONASS and BeiDou. The former is caused by higher phase noise of GLONASS and the latter is caused by wrong TEC bias estimation performed by receiver. Analysis on L2 frequency is also presented here. Some comparison and relationship between L1 and L2 scintillation parameters are done. For closer analysis, raw GPS signal is collected using event driven method. To effectively obtain useful raw signal, the system will record the raw signal only when high S4 detected. Matlab program is used to process the raw signal to obtain scintillation related parameters such as signal intensity, carrier to noise ratio (C/N0), and S4.