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The Study of GPS Total Water Vapor Content over Ubon Ratchathani
(2025-01-01)
Wongsak, Pattawut
;
Kraisi, Prasert
;
Kenpankho, Prasert
The research paper focused on learning and investigating water vapor in the atmosphere over Ubon Ratchathani, Thailand. Water vapor can be measured by using total water vapor content (TWVC) which is calculated by Global Positioning Satellites known as GPS which are over Thailand and receives signals passively which can be extracted by BG2s receiver. In this research study, Ubon Ratchathani is selected and installed BG2s receiver according to the weather and environment conditions where are among mountains, rivers, and lands with large population and agriculture occupation. TWVC can be obtained by GPS signals which are in Receiver Independent Exchange (RINEX) format. For calculating TWVC, the used altitude in troposphere over Ubon Ratchathani is five kilometers. The period of this research study was from August-October 2024 over Ubon Ratchathani. GPS datasets were analyzed and processed to Total Electron Content (TEC) estimation, converted it as ionospheric delay and estimated it as the zenith tropospheric delay (ZTD). Then, personnel at the Thai Meteorological Department (TMD) were trained and investigated the TWVC values from GPS with the TWVC values from measurement by TMD. As the results, we found that the maximum TWVC was recorded at Ubon Ratchathani in September 2024, with an average of 15.30 mm and the minimum TWVC was in October 2024, with average of 7.39 mm. The pretest and posttest were different values, which pretest score is smaller than the posttest score at 13.39. In addition, the investigation TWVC values from GPS underestimated the TWVC values from measurement by TMD at 1.5 times.
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Estimation of the single GPS-receiver bias using the gradient descent algorithm
(2016-09-06)
Chiablaem, Athiwat
;
Supnithi, Pornchai
;
Klinngam, Somjai
;
Panachart, Chaiwat
;
Saekow, Apithep
The ionospheric Total Electron Content (TEC) can be obtained from processing measurements of the dual-frequency Global Positioning System (GPS) receiver. The main sources of errors in the TEC calculation are satellite and receiver biases. In this paper, we apply the gradient descent algorithm on the receiver bias estimation. The TEC is derived from measurements at 12 dual-frequency GPS stations in Thailand. The criterion of receiver bias estimation is based on the minimum sum of the vertical TEC (VTEC) standard deviation method. The results show that the maximum receiver bias value is approximately 3.69 ns at UDON station, while the minimum value is -5.91 ns at SRTN station. The accuracy of the receiver biases from this algorithm is compared with the reference method. The maximum percentage deviation is about 7.5% at SRTN station. The percentage deviation of the minimum sum of the VTEC between the reference method and the proposed method from all stations are less than 0.05%. Thus, the proposed algorithm is a viable option to estimate the receiver bias.
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GPS satellite visibility viewed by vehicles in Bangkok, Thailand
(2007-12-01)
Kenpankho, Prasert
The novel scheme is proposed and demonstrated where satellite visibility viewed from running vehicle is economically and effectively evaluated with such low cost GPS receivers like equipped in automobiles. The preliminary experiment articulated even economical L1 C/A 1575.42MHz GPS receivers can create enough precise database of ground feature blockage, compared to fisheye photograph method, if only two statistical parameters that this research proposes are adequately set.

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