PPP and Network True Real-time 30 sec Estimation of ZTD in Dense and Giant Regional GPS Network and the Application of ZTD for Nowcasting of Heavy Rainfall

T. Iwabuchi, C. Rocken, Z. Lukes, L. Mervart, J. Johnson, M. Kanzaki

Abstract:	We have developed a true real-time ZTD processing system for GEONET (GPS Earth Observation NETwork) in Japan by using both precise point positioning (PPP) and network double-differential processing, where “true” means ZTD product availability within several seconds of GPS observations. The two processing systems are designed for potential users who need true real-time GPS tropospheric products for weather forecasts andnowcasting by monitoring current precipitable water vapor (PWV) for short-term prediction of severe rainfall. The PPP processing system first estimates satellite clocks based on zero-differenced observation in a network processing with 23 stations, and the estimated satellite clocks are used for PPP processing for more than 1,300 stations. The network processing system consists of 61 networks where each network has more than 20 stations and estimates ZTD. Both systems use IGU products and do not depend on other external observations. Four month comparison between GPS PWV and radiosonde PWV for 18 stations showed mean PWV difference of 1.3 mm and 1.2 mm for the PPP processing and network processing, and a root mean square (rms) difference of 3.8 mm and 2.4 mm, respectively. The good agreement of PWV from network processing with radiosonde PWV is better than historical comparison of radiosonde PWV with GPS PWV estimated with IGS final products in Japan. A case study when torrential rain happens in metropolitan Tokyo showed rapid increase of ZTD prior to significant rainfall. The latency of the severe rainfall relative to the ZTD increase is in the range of several tens of minutes, suggesting that frequent (30 sec) real-time ZTD estimates can provide useful information for nowcasting applications.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	1902 - 1909
Cite this article:	Iwabuchi, T., Rocken, C., Lukes, Z., Mervart, L., Johnson, J., Kanzaki, M., "PPP and Network True Real-time 30 sec Estimation of ZTD in Dense and Giant Regional GPS Network and the Application of ZTD for Nowcasting of Heavy Rainfall," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 1902-1909.
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