Characteristics of Total Electron Content (TEC) Variations at Equatorial Lonization Anomaly (EIA) during space weather activities and GPS point positioning performance | |
| Author | Sanit Arunplod |
| Call Number | AIT Diss. no.RS-16-02 |
| Subject(s) | Total Electron Content (TEC) Equatorial Lonization Anomaly (EIA) Global Positioning System |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Remote Sensing & Geographic Information Systems |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. RS-16-02 |
| Abstract | Global Positioning System (GPS) has been playing a fundamentalrole in human life every day. There has been an increased number of GPS technology users, who depend on it in numerous applications such as navigation, surveying, tracking system and time reference based on GPS clock. The Global Positioning System (GPS) is a space-based technology which presents precise time and location. It can be operatedfromanywhere, anytime and any weatherconditions where there is a line of sight for at least four GPS satellites.The radio frequency isusedas a medium for broadcasting information from the satellite to the earth continuously through the atmosphere. Many key parameterscanlead to positioning errors,e.g., Satellite clocks, orbit errors, ionosphere delay, troposphere delays, receiver noise,and multipath. Although, most of the error is attributedfrom the ionosphere which can lead from few meters to many hundred meters. There are many on-going research and technologies available to reduce or remove the possible GPS positioning errors occurring from thesesources. Ionosphere being the most unpredictable layer of the atmospheremakes it toughto remove GPS positioning errors mainlydue to the direct influence ofthe sun and its dynamic activities. Thesolar maximumand sunactivity has beenincreasing rapidly due to its 11-year solar cycle. The increase in solaractivity adversely affects Earth’s Ionosphere and GPS signals reaching ground-based receivers. These can be a major threat to GPS users worldwide. Thisresearch aims to study and analyze the diurnal, seasonal and annual variations of total electron content and scintillation index (S4) using GPS-SCINDA(Scintillation Network and Decision Aid)stations data located in Thailand during the year 2010-2012. The data used are the vertical TEC (vTEC),and S4 observed at the Bangkok (AIT, 14.079 N, 100.612 E) and Chiang Mai University (CMU, 18.480 N, 98.570 E). AIT and CMU stations are located at 4.13º N and 8.61º N magnetic latitude respectively, a region of intense equatorial ionospheric disturbances. The comparison of GPS-TEC data with TEC derived from IRI-2007 and IRI-2012 models has been in low-latitude equatorial anomaly regions. Finally, GPS positioning performance haveevaluatedduring the severe space weather events for the selected study period.The Air Force Research Laboratory of USA has established Scintillation Network and Decision Aid (SCINDA), as a set-up ofground-basedstations that monitor trans-ionospheric signals at the VHF and L-Bandfrequencies and GPS based stations. The main purpose of SCINDA is to serve as regional specification andshort-termforecasts of scintillation occurring onto VHF and L-Band frequencies,i.e., especially on communication and navigation signals. The SCINDA ground stations are positioned between the ionization crests of the Appleton anomaly, as these locations experience the strongest global levels of scintillation.GPS-SCINDA system setup comprises of a computer with both GPS-SCINDA executable and GPS-SCRIPT package installed along with the GPS receiver hardware. For this current research, the SCIDA stations in Thailand data post-processingof the relative TEC was ivperformed using the GPS TEC analysis application softwaredeveloped by Seemala and Valladares (2008) of the Institute of Scientific Research for Boston College, USA. The GPS-TEC softwareusedthe code and phase values for both L1 and L2 GPS frequencies. The analysis has removedthe effect of tropospheric water vapor and clock errors to calculate the relative values of slant TEC (Sardon and Zarraoa et al., 1997; Gao et al., 1994; Arikan et al., 2008; Sardon et al., 1994).The absolute values of TEC are obtained by including the differential biases published by theUniversity of Bern and the receiver bias that is calculated by minimizing the TEC variability between 0200LT and 0600 UT (Valladres et al., 2009). The derived TEC with biashas been stored inASCIIfiles along with other parameters defining the position of the satellite such as the IPP-latitudes, IPP-longitudes, azimuth angle, time and elevation angle. The data from AIT and CMU stations for the period August 2010 toDecember2012has been used in this research. During the of study,new sunspot regions were observed to be forming on the surface of the sun. Further, the geomagnetic indices have exhibited an extraordinaryphenomenon due tosevere space weather events. The data analysis of GPS-SCINDA station’s data has facilitated the detailedunderstanding of electrodynamics of equatorial ionospheric motions as a function of diurnal, seasonal, annual, solar cycle and latitude. International Reference Ionosphere models IRI-2012 andIRI-2007 data has been utilized and compared with the GPS TEC data obtained from the both stations. The result of research is highlyrecommended to use IRI-2012 model forGPS data comparison from 2012 onwards since it has shown improvement of 5-14% than IRI-2007. Data comparison leadsto the model validation of newly released IRI-2012 version and also able to foresee the issues occurring when dealt with data over equatorial ionospheric anomaly (EIA) region. The research work has analyzed two scenarioscases of the impacts of space weather events on GNSS positioning.In first case study,GPS point positioning atAITBstation has been analyzed duringtheperiodwhich has stormtime in single positioning mode. The result has shown the positioning accuracy during space weather events in single positioning mode can be reached up to 8-10 meters in X and Y direction and also up to 20 meters in vertical precision.The subsequentcase has analysishigherorder effect on GPS signal in SiReNTnetwork, Singapore. Thisstudy included fourstations over Singaporeas following: SNTU, SNYP, SLOY,and SSEK. The analysis part has used RINEX_HO, which developed to correct the GPS observables for a second and third-order ionosphere effects.The Space weather event hasselectedduringtheperiodofthefirstweek inMarch 2011.The resulthas evaluated the station positioningand solutions file effect on precise point positioning (PPP) processedby GIPSY-OASIS software.Thecomparisonbetween corrected-uncorrected solutions was analyzed before and after the weather spaceevent. The result of the research hasshown the higher order effect more on secondorder than third order effecton both L1 and L2 frequency.Finally the result of PPPsolutions has shown upon to sub-millimeter in the horizontaland sub-centimeterlevel in vertical precision. |
| Year | 2016 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. RS-16-02 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Remote Sensing (RS) |
| Chairperson(s) | Tripathi, Nitin Kumar |
| Examination Committee(s) | Poompat Saengudomlert ;Sarawut Ninsawat ;Raju, Durairaju Kumaran |
| Scholarship Donor(s) | Royal Thai Government ;Asian Institute of Technology Fellowship |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2016 |