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Analysis of ionospheric and geomagnetic fields changes in Thailand during the May 2024 geomagnetic storm
(2025-12-15)
Myint, Lin M.M.
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Perwitasari, Septi
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Nishioka, Michi
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Saito, Susumu
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Kaewthongrach, Rungnapa
The extreme geomagnetic storm of May 2024, the most severe in two decades of space weather history up to date, had widespread effects on the ionosphere, from the polar regions to the magnetic equator. This study examines the responses of the equatorial ionosphere and geomagnetic field over Thailand during this geomagnetic storm, utilizing data from GNSS receivers, magnetometers, and ionosondes near the magnetic equator and low-latitude regions of Thailand. We analyze the direct and indirect impacts of interplanetary magnetic field (IMF) and interplanetary electric field (IEF) variations, driven by solar storms, on local equatorial magnetic fields and ionospheric parameters. Our finding reveals that storm-driven electric fields, particularly prompt penetration electric fields (PPEF) and disturbance dynamo electric fields (DDEF), strongly influenced equatorial electric field (EEF), causing notable fluctuations in total electron content (TEC), critical frequency of F2 (foF2), and virtual height of F layer (h’F). The Pearson correlation analysis highlights the rapid coupling between interplanetary magnetic field (IMF) and local equatorial magnetic fields during geomagnetic storms. These observations enhance our understanding of geomagnetic storm impacts in equatorial regions, which is crucial for improving space weather forecasting and mitigation strategies, especially for GNSS-dependent systems and radio communications.
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Compatibility of Low-Cost GNSS Receivers for Total Electron Content (TEC) Analysis
(2025-01-01)
Rana, Bhim Bahadur
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Supnithi, Pornchai
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Myint, Lin M.M.
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Tongkasem, Napat
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Budtho, Jirapoom
Although the geodetic GNSS receivers are highly precise, they are inaccessible to every user, especially in remote areas. Therefore, this work aimed to find the reasons that bolster the low-cost GNSS receivers to be used with high resolution over a wide area, instead of geodetic in space weather studies. A comparative analysis was conducted between a low-cost Ublox ZED-F9P GNSS receiver and a geodetic Novatel Propak6 GNSS receiver, focusing on ionospheric parameters such as slant total electron content (STEC), vertical total electron content (VTEC), and the number of satellites tracked using the Global Positioning System (GPS). Additionally, VTEC values were compared with the GIM model. Both receivers exhibited a similar pattern of TEC, with the R2 value of 0.9734 and the root mean square error of 3.4583. The number of satellites tracked by both receivers during the observed periods was also found to be similar. Moreover, the VTEC results obtained from the low-cost GNSS receiver showed compatibility with the GIM model, demonstrating the reliability of the low-cost receiver in comparison to the geodetic GNSS receiver.
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Statistical analysis and effects of radio frequency interference in GPS signal quality in Thailand
(2024-10-01)
Sophan, Somkit
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Supnithi, Pornchai
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Myint, Lin M.M.
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Budtho, Jirapoom
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Saito, Susumu
The radio frequency interference (RFI) in global navigation satellite system (GNSS) signals has recently received much attention in the GNSS community because of frequent jamming issues. The carrier-to-noise density ratio (C/N<inf>0</inf>) is one of the common parameters to indicate the signal quality. In this work, we propose a real-time RFI analysis based on windowing and normalization of C/N<inf>0</inf> observations. Specifically, the percentage of RFI values are analyzed based on the modified RFI detection. The steps to analyze the RFI levels (low, medium, high) are highlighted. In addition, we analyzed the occurrences of local RFI effects in areas surrounding the Suvarnabhumi International Airport as well as remote areas. We validate the modified RFI detection by using the GNSS reference stations at the urban, suburban, and outside the capital city in Thailand. The user positioning errors with the high (severe) RFI levels are investigated based on the single point positioning (SPP) and real-time kinematics (RTK). From the experimental simulations, the high RFI levels at the urban are higher than those at the suburban. As expected, the statistical analysis covering COVID-19 (2019 to 2023) shows that the high RFI levels in June 2023 (post COVID-19) are more than those in June 2020 and 2021 (lockdown COVID-19) by about twofold. Additionally, the SPP positioning errors with the medium/high RFI levels are clearly seen. There are more floating solutions in the RTK system in the year with more RFI presence.
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Local mitigation of higher-order ionospheric effects in DFMC SBAS and system performance evaluation
(2024-04-01)
Sophan, Somkit
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Supnithi, Pornchai
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Myint, Lin M.M.
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Saito, Susumu
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Hozumi, Kornyanat
Dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) is a new SBAS standard for aeronautical navigation systems. It supports aircraft navigation from the enroute to approach phases via the L1 and L5 frequencies (1575.42 and 1176.45 MHz). Although the ionosphere-free (IF) combination in the DFMC SBAS operation removes the first-order ionospheric delays in the pseudorange measurement, remaining terms including the satellite-clock offset errors and higher-order ionospheric (HOI) delays are still unaccounted for. The DFMC SBAS accuracy and integrity can be affected by the HOI effects, especially during severe ionospheric disturbances. In this work, we present the local DFMC SBAS corrections with and without the mitigation of HOI delays. We first estimate the HOI delay terms using the received pseudorange followed by separate satellite and receiver bias estimations based on the minimum sum-variance technique. The integrity terms can then be obtained. The performances of DFMC SBAS using the global navigation satellite system (GNSS) data including GPS, Galileo, and QZSS are evaluated using obtained GNSS data at stations in Thailand on the ionospheric quiet and disturbed days. The results show that with the HOI mitigation, the vertical positioning errors (VPE) on the quiet and disturbed days can be improved by 12% and 9%, whereas the vertical protection levels (VPL) are improved by 16% and 21%, respectively. In addition, we perform a preliminary assessment of DFMC SBAS based on the International Civil Aviation Organization (ICAO) requirements of two categories: Localizer Performance with Vertical guidance (LPV-200) and Category I precision approach (CAT-I) showing promising results.
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Ground Facility Error Analysis and GBAS Performance Evaluation Around Suvarnabhumi Airport, Thailand
(2024-02-01)
Budtho, Jirapoom
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Supnithi, Pornchai
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Siansawasdi, Nattapong
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Saito, Susumu
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Saekow, Apitep
The performances of the ground-based augmentation system (GBAS) designed for the landing phase of aircraft rely on the accurate characterization of error models. Among various error sources, the multipath model, which is typically constructed by combining environmental errors at airports, must be modeled in GBAS. However, in practice, the multipath effects at a particular airport differ from other airports due to distinct construction sites and continually changing environments, resulting in an inaccurate error model in GBAS operations. Therefore, in this article, we develop and evaluate a 2-D ground facility error model from the Global Navigation Satellite System Stations (GNSS) at the Suvarnabhumi International Airport in Bangkok, Thailand. The results indicate that the elevation and azimuth grid points require around seven days of observation data to create the GBAS ground facility error model for GBAS operation. The number of observations per day at each elevation and azimuth grid point will determine the data requirements for the complete building of the 2-D ground error model. When the proposed model is applied to the GBAS simulation, it is found that the proposed 2-D ground error model reduces the root-mean-square deviation (RMSD) of positioning errors by around 0.4% to 3.5% when compared to the 1-D error model and the category B Ground accuracy designator model, respectively. The maximum vertical protection level reduction of the proposed 2-D B-value model in comparison with the reference 1-D B-value is 0.24 m, about a 6% reduction.
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Radio Frequency Interference (RFI) Analysis on GNSS Signals and Effects on Positioning Errors
(2024-01-01)
Sophan, Somkit
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Supnithi, Pornchai
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Myint, Lin M.M.
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Budtho, Jirapoom
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Saito, Susumu
Radio frequency interference (RFI) frequently exists in the Global Navigation Satellite System (GNSS) signals. Conventionally, the monitoring of carrier-to-noise density ratio (C/N0) values can be used to detect the RFI levels. Since RFI affects the quality of GNSS signals and applications, we determine three RFI levels (low, moderate, and high) based on C/N0 then statistically analyze the RFI occurrences in Bangkok, Thailand. The percentage of RFI occurrences is computed based on the average C/N0 technique. We compare the RFI occurrence statistics of 2 GNSS stations in the urban (DPT9) and suburban (KMIT) areas in Bangkok in June 2021 (COVID-19 lockdown period) and 2023 (Post COVID-19 period). The results show that during the COVID-19 period, the RFI occurrences are much reduced at the DPT9 station in the center of the city. The high (severe) RFI levels at DPT9 (urban) are mostly higher than those at KMIT station (suburban). In addition, we investigate the effects of high (severe) RFI events on single-point and real-time kinematics (RTK) positioning errors.
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Investigations of User Positioning Errors by Using Local DFMC SBAS Correction with Higher-Order Ionospheric Delay Mitigation in Thailand
(2024-01-01)
Sophan, Somkit
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Supnithi, Pornchai
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Myint, Lin M.M.
Dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) is essential to support airplane navigation. Typically, the global navigation satellite system (GNSS) with the L1 (1575.42 MHz) and L5 (1176.45 MHz) frequencies are utilized to remove the ionospheric delays based on the ionosphere-free (IF) combination (L1-L5), nevertheless, the errors due to higher-order ionospheric (HOI) delays still need to be corrected. With the local DFMC SBAS correction with a HOI mitigation in Thailand had not been considered and investigated yet. Therefore, we investigate local DFMC SBAS corrections with the HOI mitigation which are generated from the base stations in Thailand. The corrections are approximated from the local total electron content (TEC) values based on the Klobuchar model. Firstly, the local HOI days are estimated by using the observed pseudorange, and consequently, the local DFMC SBAS corrections are generated based on the minimum sum-variance technique with the IF carrier smoothing code. The GPS, Galileo, and QZSS data from the reference stations network in Thailand are utilized. In the preliminary study, the user positioning errors on the quiet days are evaluated based on the single point positioning (SPP) algorithm. The results show that both horizontal and vertical position errors are reduced by the local DFMC SBAS corrections with the HOI mitigation. The position error improvements on the quiet days can be experienced by 11%.
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Comparative Study of the Equatorial Plasma Bubbles using VHF Radar Images and Spatial ROTI Maps at Low-Latitude Region
(2023-01-01)
Tongkasem, Napat
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Myint, Lin M.M.
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Supnithi, Pornchai
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Hozumi, Kornyanat
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Nishioka, Michi
Equatorial Plasma Bubbles (EPBs) depict electron density depletion region originating at the bottom side of the F layer in the ionosphere. The EPBs are often observed in the low latitude region after post-sunset period, particularly, in equinoctial months. Since EPBs have a negative impact on high-precision positioning techniques, degrading convergence time and accuracy, it is essential to study the spatial variations of EPBs during their lifetime. In this work, we develop 2-D temporal-spatial maps based on the rate of change TEC change (ROTI) index analyzed from pseudorange information in a GNSS receiver network over Thailand. The area covers the magnetic equatorial and low-latitude regions including equatorial ionosphere anomaly (EIA). Using 2-D ROTI maps (longitude vs latitude), two types of ROTI keograms (time vs latitude and time vs longitude), we analyze the spatial and temporal changes of recent EPB events. Complementing this analysis, we propose to jointly anlayze the VHF radar images at Prachomklao Chumphon VHF radar station (Lat:10.72 N, Lon: 99.37, Magn. Lat: 1.34). The radar system can scan the ionosphere from geographic latitude 0° N to 20° N and from 140 to 860 km altitude range. The results show that with the three types of data methods, characterizations, speed, velocity and occurrences of EPB are obtained.
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Performance improvement of the GAGAN satellite-based augmentation system based on local ionospheric delay estimation in Thailand
(2022-10-01)
Sophan, Somkit
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Myint, Lin M.M.
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Saito, Susumu
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Supnithi, Pornchai
Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. L1 SBAS operates on the L1 frequency (1575.42 MHz) and is currently still of interest since all GNSS satellites and receivers do not fully support additional frequencies such as L5 (1176.45 MHz). Although the Global Positioning System (GPS) aided Geo Augmented Navigation (GAGAN) SBAS is available, the performances are degraded due to the discrepancies of the ionospheric correction over Thailand and surrounding areas. Hence, in this work, we propose a new method based on the geometry-free ionospheric delay estimation with a single frequency (L1) and a single reference station requirement. The local ionospheric delays are estimated based on the proposed method with the observed GPS and GAGAN data in Thailand. Then the ionospheric corrections are obtained from the estimated local ionospheric delays. The analysis shows that using the estimated corrections, the positioning errors are reduced both on quiet days and locally disturbed days in 2019. More reductions in the positioning errors are found in September and December than other months. In addition, we perform a preliminary availability assessment of two critical phases of flights. The GAGAN performances with the proposed method for the APV-I and LPV-200 categories are improved up to 57% and 53%, respectively, in comparison with the baseline method of the IGP correction.
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Analysis of local geomagnetic index under the influence of equatorial electrojet (EEJ) at the equatorial Phuket geomagnetic station in Thailand
(2022-09-01)
Myint, Lin M.M.
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Hozumi, Kornyanat
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Saito, Susumu
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Supnithi, Pornchai
The local K-index is an important proxy to monitor geomagnetic disturbances due to the solar wind in space weather study. The diurnal variation of geomagnetic fields observed in the magnetic equatorial region is dominated by the equatorial electrojet (EEJ), and the variation of EEJ is directly related to the local ionospheric dynamics; therefore, in this work, the local K-index is generated by based on the geomagnetic field measurement at an equatorial geomagnetic station in Phuket, Thailand and the effects of EEJ on the computed local K-indices are analyzed. At each station, an L9 (the lower limit for K = 9) value is set to develop a conversion table between the magnetic range scales and K-indices, and that L9 value must be assigned based on the characterization of the geomagnetic variations at that station. In this work, suitable L9 values are determined by analyzing the distributions of the local K-index and the planetary geomagnetic index, Kp-index. According to the results in the present study, the L9 value of 500 nT can provide local K-indices that can classify the geomagnetic disturbances more correctly. The results show that 40% of the local K-index is consistent with the Kp-index, and about 45% of the local K indices are ±1 deviated from Kp-indices. It is found that using the suitable L9 value can partially control the EEJ's dominance on K-index. Moreover, we investigated the seasonal and day-to-day variability of the diurnal variation of the geomagnetic fields from the Phuket station. Upon reviewing the data, the equatorial geomagnetic field variations were consistent with the planetary geomagnetic activity levels, and the day-to-day changes of the daytime field amplitudes were relatively high in the high solar activity year and moderate in the low solar activity year.

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