Supnithi, Pornchai

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Supnithi, Pornchai
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Supnithi, P.
Supnithi, Pomchai
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pornchai.su@kmitl.ac.th

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    Effects of Equatorial Plasma Bubbles over Real-Time Kinematic Positioning in Low-Latitude Region
    (2023-01-01)
    Thu, Phyo C.
    ;
    Supnithi, Pornchai
    ;
    Myint, Lin Min Min
    ;
    Budtho, Jirapoom
    ;
    Saito, Susumu
    Equatorial plasma bubbles (EPBs) refer to ionospheric irregularities in low-latitude regions, commonly observed after sunset. They originate at the magnetic equator and then potentially spread to mid-latitude region. As cm-level positioning techniques are increasingly important to various segments of society, the performance degradation of these systems due to EPB at low latitudes needs to be investigated. In this work, we analyze the EPB effects on the performances of real-time kinematic (RTK) positioning at the short, medium, and long baselines at low-latitude stations in Thailand. The low-latitudes local ionospheric disturbances such EPBs are shown to degrade the positioning accuracy of RTK in different seasons in 2022. It is found that the positioning errors are higher during the disturbance periods and more severe at the long baselines than the shorter ones, especially during the equinoctial months.
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    Total electron content observations by dense regional and worldwide international networks of GNSS
    (2018-06-01)
    Tsugawa, Takuya
    ;
    Nishioka, Michi
    ;
    Ishii, Mamoru
    ;
    Hozumi, Kornyanat
    ;
    Saito, Susumu
    Two-dimensional ionospheric total electron content (TEC) maps have been derived from ground-based Global Navigation Satellite System (GNSS) receiver networks and applied to studies of various ionospheric disturbances since the mid-1990s. For the purpose of monitoring and researching ionospheric conditions and ionospheric space weather phenomena, we have developed TEC maps of areas over Japan using the dense GNSS network, GNSS Earth Observation NETwork (GEONET), which consists of about 1300 stations and is operated by the Geospatial Information Authority of Japan (GSI). Currently, we are providing high-resolution, two-dimensional maps of absolute TEC, detrended TEC, rate of TEC change index (ROTI), and loss-of-lock on GPS signal over Japan on a real-time basis. Such high-resolution TEC maps using dense GNSS receiver networks are one of the most effective ways to observe, on a scale of several 100 km to 1000 km, ionospheric variations caused by traveling ionospheric disturbances and/or equatorial plasma bubbles, which can degrade single-frequency and differential GNSS positioning/navigation. We have collected all the available GNSS receiver data in the world to expand the TEC observation area. Currently, however, dense GNSS receiver networks are available in only limited areas, such as Japan, North America, and Europe. To expand the two-dimensional TEC observation with high resolution, we have conducted the Dense Regional and Worldwide International GNSS TEC observation (DRAWING-TEC) project, which is engaged in three activities: (1) standardizing GNSS-TEC data, (2) developing a new high-resolution TEC mapping technique, and (3) sharing the standardized TEC data or the information of GNSS receiver network. We have developed a new standardized TEC format, GNSS-TEC EXchange (GTEX), which is included in the Formatted Tables of ITU-R SG 3 Data-banks related to Recommendation ITU-R P.311. Sharing the GTEX TEC data would be easier than sharing the GPS/GNSS data among those in the international ionospheric researcher community. The DRAWING-TEC project would promote studies of medium-scale ionospheric variations and their effect on GNSS.
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    Ionospheric Scintillation Prediction Using Decision Tree and Rainforest Techniques
    (2024-01-01)
    Trachuentong, Sirasake
    ;
    Supnithi, Pornchai
    ;
    Myint, Lin Min Min
    ;
    Saito, Susumu
    The ionosphere contains electron density variation. When radio signals transmitted from global navigation satellite systems (GNSS) pass through such medium, additional delays are added. With ionospheric irregularity, fluctuation in GNSS signals known as scintillation are often observed resulting in reduced number of tracked satellites then degrade positioning performances. At present, scintillation is considered random, hence, the ability to detect or predict such phenomenon is crucial to efficient system operation. In this research, we design machine learning algorithm for scintillation prediction. Both Decision Tree (DT) and Random Decision Forest (RF), are implemented to predict daily ionospheric scintillation at King Mongkut's Institute of Technology Ladkrabang (KMITL) station in Thailand (13.73 ° E, 100.77° N). The rate of total electron content change index (ROTI) is also used. Modeling is carried out for four months in March (equinox), June (solstice), September (equinox), and December (solstice) in 2022, representing different seasons in space weather study. The prediction results are evaluated using the S 4 index observations at KMITL station and then compared between DT and RF methods. The designed model has a high potential for scintillation prediction.
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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.
    ;
    Perwitasari, Septi
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    Nishioka, Michi
    ;
    Saito, Susumu
    ;
    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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    Neural Network Prediction of Receiver Bias in Ionospheric Delay Computation
    (2022-01-01)
    Thu, Phyo C.
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    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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    Nominal ionospheric delay gradient estimation at Suvarnabhumi airport, Thailand
    (2017-10-19)
    Budtho, Jirapoom
    ;
    Supnithi, Pornchai
    ;
    Saekow, Apitep
    ;
    Saito, Susumu
    Ground-Based Augmentation System (GBAS) allows high-precision aircraft landing based on Global Navigation Satellite System (GNSS) at large airports. However, non-uniform spatial ionospheric delay needs to be determined. In this work, we compute the nominal ionospheric delay gradients around Suvarnabhumi airport, Thailand. The utilized techniques involve Kalman filter and LAMBDA method. Based on the measurements on DOY 043 of 2015, we found that the ionospheric delay gradients are less than 20 mm/km. With the improved ambiguity ratio test to obtain higher success rate than previous works, the standard deviation σ<inf>VIC</inf> is 5.27 mm/km.
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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
    ;
    Myint, Lin M.M.
    ;
    Saito, Susumu
    ;
    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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    Local mitigation of higher-order ionospheric effects in DFMC SBAS and system performance evaluation
    (2024-04-01)
    Sophan, Somkit
    ;
    Supnithi, Pornchai
    ;
    Myint, Lin M.M.
    ;
    Saito, Susumu
    ;
    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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    Multipath Analysis at Low-Latitude GNSS Stations around Suvarnabhumi Airport, Thailand, for GBAS Standards
    (2021-01-01)
    Budtho, Jirapoom
    ;
    Supnithi, Pornchai
    ;
    Saito, Susumu
    ;
    Siansawasdi, Nattapong
    ;
    Saekow, Apitep
    The characteristics of the local area positioning error sources are important for Ground-Based Augmentation System (GBAS) service planning. Accurate standard deviation models are required for prior simulation of the performance of the aircraft precision landing system. The multipath standard deviation of the pseudo-range errors model is used in GBAS for each satellite elevation angle. This standard model is generated by collecting the multipath conditions from airports. However, some airports have different characteristics of the multipath effects than the others, resulting in inaccurate error models when applied to the GBAS operations. Therefore, in this work, we study and analyze a 1-dimensional curve-fitted model for the multipath error models at three GNSS stations near the Suvarnabhumi International Airport, Thailand. The results show that in the case that the multipath errors are distributed equally at each azimuth angle, the RMSEs are reduced from 0.1 to 0.02 meters near the 90-degree elevation angle and less than 0.05 meters at other degrees. For the AER1 station, located on the airport runway, in which the multipath errors are not distributed equally at each azimuth, the maximum RMSE, is less than 0.08 meters when compared with 0.14 meters from the GBAS model.
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    Spatio-temporal characteristics of ionospheric irregularities in low latitude regions during the peak of solar cycle 25
    (2025-07-01)
    Tongkasem, Napat
    ;
    Supnithi, Pornchai
    ;
    Thammavongsy, Phimmasone
    ;
    Nishioka, Michi
    ;
    Perwitasari, Septi
    Equatorial plasma bubbles (EPBs) are a primary source of ionospheric irregularities (IIR) in low-latitude regions. The severity of EPBs depends on the intensity, penetration, and disturbance of electric fields generated in the ionosphere. In this work, we analyze the IIR associated with geomagnetic activity in the low-latitude region (0°N–25°N, 90°E–110°E) from 2022 to 2024. The total electron content (TEC) and the rate of TEC index (ROTI) are used to investigate the spatiotemporal characteristics of these IIRs, influenced by both local EPBs and global geomagnetic storms. During low-to-moderate geomagnetic activity, electric field penetration and disturbances have a low impact on EPB development. The high solar activity intensifies the electric field, leading to intense EPB occurrences that can affect the entire region for several hours. From January 2022 to October 2024, these intense EPB events accounted for 35% of all EPB occurrences. During strong geomagnetic storms, the prompt penetration of electric fields (PPEF), and disturbance dynamo electric field (DDEF) caused the depression and fluctuations of TECs.