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Author: search.filters.author.Hozumi, KornyanatSubject: search.filters.subject.ionospheric delay

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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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    The disturbance effects on single frequency GPS positioning at low geomagnetic latitude stations in Thailand
    (2020-07-01)
    Tongkasem, Napat
    ;
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    ;
    Komolmis, Tharadol
    ;
    Hozumi, Kornyanat
    The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. In the positioning system, the atmosphere is the main medium along the propagation path that includes some ions, water vapor, and noise. These are the causes of the propagation delay time especially the ions in the ionosphere. At the present, there are many Global Positioning System (GPS) stations worldwide. Therefore, we can check the performances of the positioning system by using the positioning error calculation. In this work, the positioning errors are calculated from the 16 GPS stations at the low geomagnetic latitude region (Thailand) with the single frequency algorithm on a disturbance day. Then, we compute the 95-percentile and the maximum of the positioning errors. The results show approximately the difference of 95-percentile value 1.799 meters on the horizontal axis and 2.289 meters on the vertical axis and maximum positioning error can be up to 11.413 meters on the disturbed time on the disturbance day.
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    The comparison of Klobuchar model with GPS TEC model at the low geomagnetic latitude station, Thailand
    (2019-06-01)
    Tongkasem, Napat
    ;
    Supnithi, Pornchai
    ;
    Phakphisut, Watid
    ;
    Hozumi, Kornyanat
    ;
    Tsugawa, Takuya
    In the Global Positioning System (GPS), ionospheric delay time is a main cause of the positioning system errors. We can typically calculate the ionospheric delay using the dual-frequency receivers (L1: 1,575.42 MHz, L2: 1227.60 MHz). The Klobuchar model is a well-known model developed to estimate the ionospheric delay and currently used for single-frequency users. The coefficients of the model are daily broadcast in the GPS satellite navigation message for worldwide users. In this work, we compare the actual ionospheric delays with the Klobuchar model to observe the differences at 4 stations in Thailand: CMU (Chiang Mai), KMIT (Bangkok), CPN (Chumpon) and NNKI (Nongkai) on 10 February 2018 (no disturbance). Then, we compute the new Klobuchar coefficients from the comparisons. The proposed Klobuchar coefficients can correct the RMSE of the original model by 32.4, 36.5, 28.5 and 37.1 at KMIT, CPN, NNKI and CMU station, respectively. The RMSE of the new Klobuchar and observed TEC comparison are 24.0718, 28.5849, 21.6086 and 27.7273, respectively.