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Author: search.filters.author.Ansari, KutubuddinSubject: search.filters.subject.Klobuchar model

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    Ionospheric gradients in multi-constellation global navigation satellite system signals onboard UAV using GIM and Klobuchar model over Thailand region
    (2026-07-01)
    Ansari, Kutubuddin
    ;
    Panda, Sampad Kumar
    ;
    Venkatesh, Kavutarapu
    ;
    Jamjareegulgarn, Punyawi
    The effects of the ionosphere on Global Navigation Satellite System (GNSS) signals have been a focal point of research nowadays. During adverse ionospheric conditions, ionospheric gradients become more pronounced and disruptive compared to quiet days, potentially leading to increased positioning errors or loss of satellite signal lock. We introduce an ionospheric spatial gradient estimation method to detect the anomalous gradients from multi-constellation GNSS signals (i.e., GPS, GLONASS, and Galileo) signals recorded by the onboard sensor of flying real-time kinematic unmanned aerial vehicle (RTK UAV) over the Thailand region. We employ the Klobuchar model and global ionospheric maps (GIMs) for estimating the slant total electron contents (STECs) and the corresponding ionospheric spatial gradients between base station and rover (RTK UAV) receivers among the studied multi-constellation systems. The results show that the STEC values estimated from IGS-GIM are larger than those computed by Klobuchar model. Such kind of gradient variation cannot show a perfect correlation due to limited accuracy of Klobuchar model parameters. As for our analysis, the ionospheric spatial gradients estimated from GPS satellites are higher than those calculated from GLONASS and Galileo satellites due to the smallest differences between the two successive positions of flying rover estimated from GPS satellites. The outcomes from this study complement the multi-GNSS cooperative strategy for monitoring ionospheric gradients, thereby mitigating the adverse effects in dynamic positioning and navigation solutions over low-latitude regions.
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    Applicability of Klobuchar Model for STEC Estimation Over Thailand Region
    (2023-01-01)
    Srisamoodkham, Worachai
    ;
    Ansari, Kutubuddin
    ;
    Jamjareegulgarn, Punyawi
    In the current study, we investigated the total electron content (TEC) variations over Thailand region by using five multi-constellation Global Navigation satellite system (GNSS) signals. The STEC variations for all multiple GNSSs were computed with well-known ionospheric Klobuchar model and compared with the STEC values of Global Ionospheric map (GIM) on a storm day (May 12, 2021), before as well as after this storm day. The results showed that most of the GIM STEC values (GSVs) were overestimated with the Klobuchar model STEC values (KMSVs) for all constellations, except QZSS. As for the QZSS, the KMSVs were closest to the GSVs. Likewise, the MS-SHF-based Klobuchar model (MSSHFKM method) was able to compensate the ionospheric delay effectively as compared to the original Klobuchar model up to 77.08% RMSE during the geomagnetic storm on May 12, 2021.
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    Positioning Comparison Using GIM, Klobuchar, and IRI-2016 Models During the Geomagnetic Storm in 2021
    (2022-01-01)
    Srisamoodkham, Worachai
    ;
    Ansari, Kutubuddin
    ;
    Jamjareegulgarn, Punyawi
    This paper compares the positioning accuracy obtained from the GIM VTEC, the Klobuchar model, and the IRI-2016 model at Chiang Mai and DPT9 stations, Thailand, during an intense geomagnetic storm of 2021 (on May 12, 2021). The results show that the diurnal variation of the Klobuchar modeled VTECs show the same trend as that of the observed GIM VTECs with the same peaks and the maximum deviation of 22.5% at 05:00 UT. Meanwhile, the IRI2016-predicted VTECs show its peak at 07:00 UT and are not available obviously during 13:00–21:00 UT due to the impact of this intense geomagnetic storm. Most of the ionospheric delays obtained from the Klobuchar model underestimate those of the GIM VTEC, whereas they overestimate those of GIM VTEC during after midnight and pre-sunrise period. At both stations, the mean ionospheric range delays of the GIM VTEC are highest during daytime period while those of the IRI-2016 model are largest during nighttime period. The positioning errors at higher latitude (CHMA station) are larger than those at lower latitude (DPT9 station).