Abstract
GPS-based Zenith Tropospheric Delay (ZTD) estimation should be easily obtained in a cost-effective way, however, the most previous studies focus on post-processed ZTD estimates using satellite orbit and clock products with at least 3–9 hours latency provided by International GNSS Service (IGS), which limits the GNSS meteorological application for nowcasting. With the development of IGS’s real-time pilot project (RTPP), this limitation was removed by April, 2013 as real-time satellite orbit and clock products can be obtained on-line. In this paper, on the one hand, the GPS-derived ZTD estimation was evaluated using the IGS final and real-time satellite products based on independently developed PPP software. On the other hand, the analysis of the time series of GPS-derived ZTD by least-square fitting of a broken line tendency for a full year of observations, and a forecasting method for precipitation is proposed based on the ZTD slope in the ascending period. The agreement between ZTD slope and the ground rainfall records suggested that the proposed method is useful for the assisted forecasting, especially for short-term alarms.
Highlights
Global Navigation Satellite System (GNSS) meteorology was proposed in 1990s, and has proved to be a powerful tool in atmospheric water vapour research from micro-meteorology to global climate studies[1,2,3,4]
With the developments made in the International GNSS Service (IGS) real-time pilot project (RTPP)[20], precise clock and orbit products without time latency can be downloaded on-line[21], which promotes the rapid development of real-time PPP techniques and makes it easy to obtaining real-time Zenith Tropospheric Delay (ZTD)/precipitable water vapour (PWV) products[22,23,24,25]
In the first part of this paper, the accuracy of post-processed ZTD derived from the independent developed PPP software was compared with the ZTD derived from GAMIT, Bernese PPP model and very long baseline interferometry (VLBI), the real-time satellite orbit and clock products provided by real-time service (RTS) were evaluated with respect to the IGS final orbit and clock products and the real-time GPS-derived ZTD was compared with the post-processed GPS-derived ZTD
Summary
The mean and RMS error were calculated for the differences between the two PWV time series, and the final data was selected using those differences less than three-times the RMS error The GPS data of station LJSL was processed by the newly developed PPP software using the IGS final orbit and clock products to obtain the estimated ZTD, ZHD, and PWV on an hourly basis. To validate the reliability and stability of the proposed precipitation forecasting method, the selected threshold of ZTD slope mentioned above for station ZJZS was used using a full year of hourly PWV and precipitation event data. The large variation in water vapour content was embodied by the large change in ZTD, which leads to a relatively high false alarm rate
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