The Study of GPS Total Water Vapor Content over Ubon Ratchathani

Abstract

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.