Determination of GPS Tropospheric Delays by Utilizing Ground-based GPS Network Measurements and its Applications for Weather Forecasts and Precise Point Positioning

D. Kim, K-D. Park

Abstract:	The delay occurs while GPS signals pass through the ionosphere and troposphere and it decreases the accuracy of GPS positioning. Therefore, it must be eliminated for GPS precise point positioning (PPP). Through studies on tropospheric delay measurements of the GPS signal, it is now possible to apply the technology of GPS network measurements to weather forecasts. Recently, the Korea Meteorological Administration (KMA) has introduced GPS precipitable water vapor (PWV) to numerical weather predictions. KMA have been using upper-air observation systems to observe atmospheric water vapor, such as radiosonde and radiometer. However, these observation networks weren't dense enough to analyze the rapid change in under-synoptic scale atmosphere. The network of GPS is dense enough in Korea, and it can be an alternative of upper air observation method. To calculate GPS PWV, we need air pressure and temperature measurements at GPS station. About 100 GPS permanent stations are being operated in Korea. However, only 10 GPS permanent stations have their own weather sensors connected to the GPS receiver. To overcome this limitation, interpolation of pressures and temperatures from nearby automatic weather station (AWS) is needed for the GPS station without a meteorological sensor. In this study, we compared Kriging and reverse sea level correction (RSLC) to verify which the suitable AWS interpolation method is. Eventually, RSLC showed more accurate result. The root mean square error (RMSE) of RSLC was 0.2 hPa and 1.2 ?, on the other hand, Kriging's RMSE were 1.3 hPa and 1.8 ?. We calculated GPS PWV by using GIPSY 5.0 and evaluated the PWV accuracy by comparing with PWVs from radiosonde and radiometer. The RMSE of GPS PWV was about 3 mm as compared with radiosonde or radiometer. We calculated GPS PWVs during severe weather periods and analyzed the characteristics of atmospheric water vapor changes. We suggested a new tropospheric delay correction model based on zenith total delay (ZTD) from GIPSY processing result. The model provides tropospheric delay correction to GPS users into grid map structure. To make the tropospheric delay grid map, we calculated ZTDs of each GPS site in Korean Peninsula. Then, we interpolated the ZTDs by using inverse distance weighting (IDW) algorithm to calculate the values of grid points. The tropospheric delay correction model consists of zenith hydrostatic delay (ZHD), zenith wet delay (ZWD) and ZTD. As the result of tropospheric delay model accuracy analysis, the RMSE between grid map data and GPS site data was 0.7mm in ZHD, 7.6mm in ZWD and 8.5mm in ZTD. Finally, we applied the model to single frequency relative positioning algorithm and analyzed the positioning accuracy enhancement. As the result, positioning accuracy was improved up to 36% in case of relative positioning of Suwon(SUWN) and Mokpo(MKPO), that the baseline distance was about 297km.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	1795 - 1801
Cite this article:	Kim, D., Park, K-D., "Determination of GPS Tropospheric Delays by Utilizing Ground-based GPS Network Measurements and its Applications for Weather Forecasts and Precise Point Positioning," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 1795-1801.
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