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Estimation and Validation of Vertical Total Electron Content Using Standalone Single-Frequency Observations
(2022-01-01)
Tongkasem, Napat
;
Myint, Lin Min Min
;
Supnithi, Pornchai
Nonuniform ionospheric delay is a well-known cause of degradations in radio wave propagations such as in satellite communication and positioning. In general, the ionospheric delay can be estimated using the Global Navigation Satellite System (GNSS) data from dual or multiple-frequency receivers; however, satellite differential code biases (DCBs) must be downloaded via network connection. For positioning based on standalone single-frequency receivers, the Klobuchar model, a well-known model in the GPS positioning system, is used to estimate the ionospheric delay based on solar activity, season, or region by using the eight coefficients in the broadcast navigation message. Although this model can reduce positioning errors by about 50 percent, the low-latitude disturbances such as the equatorial plasma bubble (EPB) phenomenon, significantly diminishes the accuracy of modeled delay estimation. In this work, we propose an ionospheric delay estimation technique based on observed single-frequency GPS data without requiring network-based corrections for DCB. The ionospheric delays estimated by the proposed method are compared with those from the GPS dual-frequency observation, the broadcast/network models in 2014 (high solar activity) and 2020 (low solar activity). According to the results, the proposed ionospheric delay estimation can correct the ionosphere errors better than the well-known Klobuchar model, by about 9.98 percent and 6.77 percent in 2014 and 2020, respectively. The proposed model increases the ionospheric error correction efficiency in vertical positioning by up to 81 percent in 2014 and 79 percent in 2020.
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Precise total electron content map monitoring in low latitude region
(2022-01-01)
Tongkasem, Napat
;
Myint, Lin M.M.
;
Supnithi, Pornchai
The need for accurate Global Navigation Satellite System (GNSS) positioning is necessary for GNSS applications such as Real-Time Kinematic (RTK), Precise Point Positioning RTK (PPP-RTK), etc. The ionosphere delay, especially in low latitude region, is a main cause of positioning error. The usage of electron maps in GNSS applications can help with the first ionosphere correction. The Global Ionosphere Map (GIM) is a large-scale service for the Total Electron Content (TEC) with a resolution of 2.5 for latitude and 5 for longitude which may not be proper to high resolution GNSS applications in the small or regional regions. Over the low latitude region, we apply the local TEC from 4 stations which has similar longitude to observe the differential TEC. Then, we generate the precise grid TEC maps from 18 GNSS stations with different resolution of grid for observe the appropriate values. The results are shown that the resolution of 1.5 for latitude and 3 for longitude has RMS 1.58 of TECu compare with the local TEC value, while GIM has RMS of 2.11 TECu.
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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
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Komolmis, Tharadol
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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.

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