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    Equatorial Ionospheric Irregularity Detection and Analysis Using 2-D ROTI Maps and VHF Radar Images During the Upcoming Solar Maximum
    (2026-01-01)
    Supnithi, P.
    ;
    Myint, L. M.M.
    ;
    Tongkasem, N.
    ;
    Thanakulketsarat, T.
    ;
    Nishioka, M.
    In this work, we analyze the ionospheric irregularities at Chumphon station, Thailand, using observational data from GNSS receivers as well as VHF radar and ionosonde at Chumphon station, Thailand. The ionospheric irregularity event on 20 March 2020 and the super solar storms during 8–12 May 2024 are studied. Both instruments show traces the irregularities and interesting daytime fluctuation in total electron content over Thailand area. The statistics of ionospheric irregularities from 2020 to 2024 show that as we enter the solar maximum of the 25<sup>th</sup> solar cycle, more occurrences of ionospheric irregularities are clearly seen.
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    The Study of GPS Total Water Vapor Content over Ubon Ratchathani
    (2025-01-01)
    Wongsak, Pattawut
    ;
    Kraisi, Prasert
    ;
    Kenpankho, Prasert
    The research paper focused on learning and investigating water vapor in the atmosphere over Ubon Ratchathani, Thailand. Water vapor can be measured by using total water vapor content (TWVC) which is calculated by Global Positioning Satellites known as GPS which are over Thailand and receives signals passively which can be extracted by BG2s receiver. In this research study, Ubon Ratchathani is selected and installed BG2s receiver according to the weather and environment conditions where are among mountains, rivers, and lands with large population and agriculture occupation. TWVC can be obtained by GPS signals which are in Receiver Independent Exchange (RINEX) format. For calculating TWVC, the used altitude in troposphere over Ubon Ratchathani is five kilometers. The period of this research study was from August-October 2024 over Ubon Ratchathani. GPS datasets were analyzed and processed to Total Electron Content (TEC) estimation, converted it as ionospheric delay and estimated it as the zenith tropospheric delay (ZTD). Then, personnel at the Thai Meteorological Department (TMD) were trained and investigated the TWVC values from GPS with the TWVC values from measurement by TMD. As the results, we found that the maximum TWVC was recorded at Ubon Ratchathani in September 2024, with an average of 15.30 mm and the minimum TWVC was in October 2024, with average of 7.39 mm. The pretest and posttest were different values, which pretest score is smaller than the posttest score at 13.39. In addition, the investigation TWVC values from GPS underestimated the TWVC values from measurement by TMD at 1.5 times.
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    Ionospheric–Thermospheric Responses to Geomagnetic Storms from Multi-Instrument Space Weather Data
    (2023-05-01)
    Shahzad, Rasim
    ;
    Shah, Munawar
    ;
    Tariq, M. Arslan
    ;
    Calabia, Andres
    ;
    Melgarejo-Morales, Angela
    We analyze vertical total electron content (vTEC) variations from the Global Navigation Satellite System (GNSS) at different latitudes in different continents of the world during the geomagnetic storms of June 2015, August 2018, and November 2021. The resulting ionospheric perturbations at the low and mid-latitudes are investigated in terms of the prompt penetration electric field (PPEF), the equatorial electrojet (EEJ), and the magnetic H component from INTERMAGNET stations near the equator. East and Southeast Asia, Russia, and Oceania exhibited positive vTEC disturbances, while South American stations showed negative vTEC disturbances during all the storms. We also analyzed the vTEC from the Swarm satellites and found similar results to the retrieved vTEC data during the June 2015 and August 2018 storms. Moreover, we observed that ionospheric plasma tended to increase rapidly during the local afternoon in the main phase of the storms and has the opposite behavior at nighttime. The equatorial ionization anomaly (EIA) crest expansion to higher latitudes is driven by PPEF during daytime at the main and recovery phases of the storms. The magnetic H component exhibits longitudinal behavior along with the EEJ enhancement near the magnetic equator.
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    Neural Network Prediction of Receiver Bias in Ionospheric Delay Computation
    (2022-01-01)
    Thu, Phyo C.
    ;
    Supnithi, Pornchai
    ;
    Min Myint, Lin Min
    ;
    Saito, Susumu
    ;
    Saekow, Apitep
    An important measure typically used to understand ionosphere properties and disturbances is total electron content (TEC). A typical approach to calculating the ionospheric TEC is by analyzing dual-frequency GPS data. Satellite and receiver biases are the primary discrepancies in TEC computation. In this work, we develop a neural network to predict the instrumental receiver bias based on slant TEC. The minimum standard deviation method is used to calculate the receiver bias. Neural network with two hidden layers is trained with datasets and then used to predict the receiver bias. The predicted receiver bias from the proposed neural network differs from the baseline method by about 10 to 20 percent.
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    Study of GPS instrumental bias and TEC estimations from GPS stations in Thailand
    (2017-11-03)
    Chiablaem, Athiwat
    ;
    Phakphisut, Watid
    ;
    Supnithi, Pomchai
    The Total Electron Content (TEC) or satellite delay can be derived from the dual-frequency of Global Positioning System (GPS). The error of TEC accuracy suffers seriously from the GPS instrumental biases, including satellite bias and receiver bias. In this paper, we apply the singular value decomposition (SVD) to derive TEC, GPS satellite and receiver biases from the 11 GPS receiver stations in Thailand, which are operated by DPT. From the results, the daily satellite bias range between -8 ns and 10 ns. The estimated receiver bias varies from -5.03 ns to 1.88 ns. The biases in TEC are removed. The TEC estimation by SVD method is a good agreement level at each locations. The TEC of SVD estimation is compared with a TEC of general calculation by a GPS receiver from DPT9. The estimated TEC by SVD method at Bangkok area is used. The trend of both TEC are concurrence. Thus, the SVD method can be used to estimate the TEC, GPS satellite and receiver biases in Thailand area.
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    GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake
    (2006-08-01)
    Otsuka, Y.
    ;
    Kotake, N.
    ;
    Tsugawa, T.
    ;
    Shiokawa, K.
    ;
    Ogawa, T.
    We report the response of the ionosphere to the large earthquake that occurred in West Sumatra, Indonesia, at 0058 UT on December 26, 2004. We have analyzed Global Positioning System (GPS) data obtained at two sites in Sumatra and at three sites in Thailand to investigate total electron content (TEC) variations. Between 14 and 40 min after the earthquake, TEC enhancements of 1.6-6.9 TEC units (TECU) were observed at subionospheric points located 360-2000 km north of the epicenter. From the time delays of the observed TEC enhancements, we find that the TEC enhancements propagated northward from the epicenter. The time delays between the earthquake and rapid increases in TEC, which occurred near the epicenter, are consistent with the idea that acoustic waves generated by the earthquake propagated into the ionosphere at the speed of sound to cause the TEC variations. A small TEC enhancement of 0.6 TECU was observed south of the epicenter, while no TEC enhancements were seen east of the epicenter. From a model calculation, we find that this directivity of the TEC variations with respect to the azimuth from the epicenter could be caused partially by the directivity in the response of the electron density variation to the acoustic waves in the neutral atmosphere. © 2006, The Seismological Society of Japan, Society of Geomagnetism and Earth, Planetary and Space Sciences, The Volcanological Society of Japan, The Geodetic Society of Japan, The Japanese Society for Planetary Sciences. All rights reserved.