The Research on Four-Dimensional Water Vapor Tomography Based on Real-Time PPP Technique

With the development of International GNSS Service (IGS) real-time pilot project (RTPP) acquiring precipitable water vapor (PWV) with high accuracy has become a reality based on the real-time precise point pointing (RT-PPP) technique. The accuracy of zenith total delay (ZTD) and PWV derived from RT-PPP have been validated using observed global positioning system (GPS) data and meteorology data from Satellite Positioning Reference Station Network (SatRef) in 2014. The ZTD comparison with that from afterwards PPP and GAMIT software shows that the relative coefficients are 0.9786 and 0.9687, respectively. The PWV comparison with that from radiosonde shows that the relative coefficient and RMS are 0.9512 and 2.13 mm, respectively. It is a clear evidence that the RT-PPP technique has a similar accuracy with the result calculated using afterwards IGS products. However, PWV is mean of water vapor information of many GNSS signal rays during a period of time over the station, which cannot reflect the three-dimensional water vapor distribution. Slant water vapor (SWV) can be obtained by mapping PWV at different elevation and azimuth angles. The tomographic experiment has been performed using SWVs of twelve stations from SatRef as tomographic observation and compared with result from radiosonde. The comparison shows a good agreement and the RMS, SD, Bias, and MAE of integrated water vapor (IWV) are 3.60, 2.78, 2.29, and 2.92 mm, respectively, the root mean square (RMS), standard deviation (SD), Bias, and mean absolute error (MAE) of calculated water vapor density are 1.08, 1.03, −0.21, and 0.77 g/m³, respectively. The above result makes it possible that acquiring the real-time three-dimensional water vapor distribution using tomography approach with SWVs derived from RT-PPP technique, which has an important influence on short-term disastrous weather and now-casting precipitation forecasting.