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Author: search.filters.author.Phakphisut, WatidSubject: search.filters.subject.GPS

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    Improvement of single point positioning accuracy by using GAGAN satellite-based augmentation system in Thailand Region
    (2021-05-19)
    Sophan, Somkit
    ;
    Phakphisut, Watid
    ;
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    Although GAGAN satellite-based augmentation system (SBAS) provides ionospheric correction service to India and surrounding areas, the correction values do not cover the entire region of Thailand and even at provided grids, they may not be sufficiently accurate. Hence, this work, we propose a local ionospheric delay estimation method based on the geo-free ionospheric delay estimation. Then the estimated ionospheric delays are applied together with the fast and long-term corrections of GAGAN SBAS to improve the positioning errors. The results show that the estimated ionospheric delays can improve the user positioning errors in terms of horizontal and vertical errors up to 0.5 and 1 meter, respectively.
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    Performances of GAGAN Satellite-Based Augmentation System in Thailand Region
    (2020-07-01)
    Sophan, Somkit
    ;
    Phakphisut, Watid
    ;
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. Satellite-Based Augmentation System (SBAS) is vital to air navigation in many regions around the world. In Thailand, the L1-frequency SBAS corrections can be received from the GPS Aided Geo Augmented Navigation (GAGAN) system which is intended for use over Indian airspace. In this work, we analyze the performances of the GAGAN system in Thailand on quiet and disturbed days in March 2019 by applying the entire corrections received at King Mongkut's Institute of Technology Ladkrabang station. The 95-percent horizontal and vertical accuracies on quiet days are 1.52 and 3.18 meters, respectively. In contrast, on disturbed days they are 1.97 and 3.41 meters, respectively.
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    New receiver bias calculation for total electron content (TEC) in Bangkok, Thailand
    (2018-07-02)
    Tongkasem, Napat
    ;
    Supnithi, Pornchai
    ;
    Phakphisut, Watid
    Ionospheric delay is an important parameter which affects the positioning accuracy of Global Navigation Satellite System (GNSS). It can be analyzed from the total electron content (TEC) in the signal propagation path, computed from the code and carrier phase of at least dual-frequency GNSS signals. Although TEC models have previously been developed by several models including the Global Ionospheric Map (GIM), International Reference Ionosphere (IRI) and Klobuchar model for equatorial region, the estimation of TEC may not be as accurate as in other regions due to relatively fewer research studies as well as unique ionospheric characteristics at these latitudes. Generally, computed slant TECs need to be adjusted for satellite and receiver biases, the latter is dependent upon receivers and receiver location. Therefore, this study proposed the new receiver bias calculation algorithm which can deal with these problems including cycle slips, outlier data, and missing data. In particular, the TEC is computed from code pseudo range only, while the receiver bias is computed from both code and carrier phase together with the elevation angle restriction above 60 degrees (to reduce the cycle slip issue). To verify the proposed algorithm, TEC values at KMIT station (latitude = 13.73<sup>o</sup>, longitude = 100.77<sup>o</sup>), located in an equatorial region, in 2016 are estimated during 4 seasons. The TEC results are with those of International GNSS Service (latitude = 13.74<sup>o</sup>, longitude = 100.5<sup>o</sup>) and the global ionospheric map (at grid position: latitude = 13.7<sup>o</sup>, longitude = 100<sup>o</sup>) based on the Root Mean Square (RMS) error. The results evidently demonstrated that the averages of RMS are 20.60% and 10.99% for GIM and IGS, respectively.