Abstract
In this study, the performance of different processing software and strategies on the estimation of Zenith Wet Delay (ZWD) from Iran Permanent GPS Network (IPGN) was evaluated. For this purpose, GAMIT (version 10.4) and Bernese (version 5.0) software were used to estimate the ZWD values in baseline and Precise Point Positioning (PPP) mode, respectively. Then, the GPS ZWD time series in Tehran, which is the only International GNSS Service (IGS) station in Iran, were validated with the corresponding values derived from the measurements of the nearby radiosonde site at Mehrabad airport. Based on one year of estimates in both network (or baseline) and PPP mode, the GPS and radiosonde ZWD were consistent with a mean bias of 6 mm and standard deviation of 12 mm. furthermore, the IGS final tropospheric products over 2011 were used to validate our GPS data processing in this study. The Results showed that there is a good agreement between our estimates and those obtained from IGS with a mean bias of less than 1 mm. Comparing PPP with the network GPS ZWD solutions in 15 stations of IPGN over one year, showed that two methods are consistent with mean bias and standard deviation of less than 2 and 5 mm. Finally, to examine the operational usage of IPGN tropospheric products, using the IGS ultra-rapid orbits the near real time ZTD were estimated and compared with final post processed solutions. For all stations, the near real time ZTD estimation results were comparable with the corresponding post processed estimates in terms of bias and standard deviation. The obtained correlation coefficient between final and near real time solutions was more than 0.95. These results suggest that ZTD derived from Iranian regional GPS network has the potential to incorporate in different meteorological applications .
Highlights
Water vapor is an important greenhouse gas of the atmosphere which plays a key role in many atmospheric processes such as cloud formation, the hydrological cycle and precipitation systems [Jacob, 2001]
In order to investigate the effect of processing strategy on the estimation of tropospheric delay, the Global Positioning System (GPS) data were processed using GAMIT version 10.4 and Bernese version 5.0 software in baseline and Precise Point Positioning (PPP) processing mode, respectively
By the processing of GPS data over 2011 for 15 Iran Permanent GPS Network (IPGN) permanent stations, we compared tropospheric delay values estimated by different software to evaluate the effect of processing methodology
Summary
Water vapor is an important greenhouse gas of the atmosphere which plays a key role in many atmospheric processes such as cloud formation, the hydrological cycle and precipitation systems [Jacob, 2001]. The atmospheric water vapor is highly variable at different scales of time and space [Dai et al, 2002]. High-resolution observations of this parameter are necessary to monitor the spatio-temporal variation of the atmospheric water vapor and use of this information in Numerical Weather Prediction (NWP) models [Zhang and Zhan, 2007]. There are various techniques to measure the atmospheric water vapor content. Radiosonde as a conventional tool observes the atmospheric water vapor. Due to the high cost for each lunch, radiosondes often provide observations of the water vapor twice a day only. Low temporal and spatial heterogeneity of the radiosonde measurements is not suitable for studying the atmospheric water vapor variations at different scales of time and space.
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