Comparison of Precipitable Water Derived from Ground-Based GPS Measurements with Radiosonde Observations over the Korean Peninsula

Abstract

Precipitable water (PW) obtained from a permanent ground-based Global Positioning System (GPS) network on the Korean Peninsula was evaluated by using radiosonde measurements for two years. The GPS-derived PW is also validated using 5-min and 2-hourly troposphere products from International GNSS Service (IGS). The GPS-derived PW from our analysis and the IGS products were reasonably consistent with mean bias (Ours minus IGS products) of- 0.27 mm and a standard deviation of 0.78 mm. The PW derived from radiosonde measurement (radiosonde PW) shows dry bias relative to GPSderived PW, where the mean bias (GPS minus radiosonde) is 1.50 mm with a standard deviation of 2.45 mm. We also found systematic bias in radiosonde PW depending on the radiosonde launch time. At the site with 6-hourly high temporal resolution soundings, the bias is greater during day (0900 and 15 LST) than at night (2100 and 0300 LST) with a difference of 1.34 mm in the maximum. In addition, our results show the dependency of error statistics on the absolute amount of PW and seasons. The bias increased for large amounts of PW especially in the daytime. Standard deviation tended to increase under humid conditions, but does not vary with observation time. The possible bias in GPS-derived PW caused by un-modeled phase center variation is also simulated in this study. Most phase observation errors are attributed to multi-path effects caused by the structure of monuments, where the errors are relatively small against the dry biases found in radiosonde PW. Our results addressed the accuracy of GPS-derived PW with reasonable quality and showed strong temporal and spatial variability of PW due to geographic location. These results suggest that GPSderived PW produced by the Korean regional GPS network has great potential to be used for various meteorological applications and could also contribute global GPS climatology.