Diurnal Variation of Precipitable Water Vapor Based on GPS Observations

摘要

GPS observation has been performed since August, 2001 at Khon Kaen in Northeast of Thailand to obtain the Precipitable Water Vapor (PWV) and to understand the characteristics of its seasonal and diumal changed. A Trimble 4000 Ssi receiver and a Trimble microcentered L1/L2 antenna were used for the observation. The GPS data were recorded by every 30 second for 24 hours a day. The three hourly PWV were calculated from the Zenith Tropospheric Delay (ZTD). The surface meteorological measurements (air pressure and temperature) were mainly obtained from Thai Meteorological Department. The results show that the variation of PWV changed with a large amplitude (vary from 20 to 60 mm.). For dry season, PWV was increased before rain and decreased after rain. It is found that, in wet season PWV was almost constant at about 60 to 70 mm. The variation of precipitable water vapor change was small in the wet season because of nearly saturated water in the atmosphere supply continuosly by monsoon. The comparison of diurnal variation of PWV were examined between dry and wet season. The results showed that the difference of diurnal change of the two seasons was small and PWV had the minimum value at 4-7 am in the morning, it increased from the afternoon to the midnight.