Real Time PPP
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Recent papers in Real Time PPP
The use of observations from Global Navigation Satellite Systems (GNSS) in operational meteorology is increasing worldwide due to the continuous evolution of GNSS. The assimilation of near real-time (NRT) GNSS-derived zenith total delay... more
The use of observations from Global Navigation Satellite Systems (GNSS) in operational meteorology is increasing worldwide due to the continuous evolution of GNSS. The assimilation of near real-time (NRT) GNSS-derived zenith total delay (ZTD) estimates into local, regional and global scale numerical weather prediction (NWP) models is now in operation at a number of meteorological institutions. The development of NWP models with high update cycles for nowcasting and monitoring of extreme weather events in recent years, requires the estimation of ZTD with minimal latencies, i.e. from 5 to 10 minutes, while maintaining an adequate level of accuracy for these. The availability of real-time (RT) observations and products from the IGS RT service and associated analysis centers make it possible to compute precise point positioning (PPP) solutions in RT, which provide ZTD along with position estimates. This study presents a comparison of the RT ZTD estimates from three different PPP software packages (G-Nut/Tefnut, BNC2.7 and PPP-Wizard) to the state-of-the-art IGS Final Troposphere Product employing PPP in the Bernese GPS Software. Overall, the ZTD time series obtained by the software packages agree fairly well with the estimates following the variations of the other solutions, but showing various biases with the reference. After correction of these the RMS differences are at the order of 0.01 m. The application of PPP ambiguity resolution in one solution or the use of different RT product streams shows little impact on the ZTD estimates. Discussion and Conclusions The RT PPP ZTD estimates from three different software packages were compared using the IGS Final Troposphere Product as reference. In terms of standard deviation, it was seen that the solution from the G-Nut/Tefnut software library has the best agreement with the reference. After G-Nut/Tefnut solutions, the solutions from BNC2.7 are the next closest to the reference. Among the BNC2.7 solutions, a lower bias has been found for the solution computed using the correction stream containing Kalman Filter combination (IGS02) rather than the one computed using a single epoch solution correction stream (IGS01). The ambiguity float solution from the PPP-Wizard has the largest bias with the reference because of the fact that it currently does not apply corrections for receiver antenna phase centre offsets during processing. Integer ambiguity resolution using the PPP-Wizard seems to have a millimeter level effect on the RT PPP ZTD estimates. The RT PPP ZTD solutions were compared to the established user requirements for nowcasting by using RMS bias to IGFT as a measure of relative accuracy. It was seen that GN01, GN02, GN91 and BN02 fulfill the threshold requirements on ZTD accuracy whereas BN01, and PWFL (and PWFX) exceed this threshold.
The continuous evolution of global navigation satellite systems (GNSS) meteorology has led to an increased use of associated observations for operational modern low-latency numerical weather prediction (NWP) models, which assimilate... more
The continuous evolution of global navigation satellite systems (GNSS) meteorology has led to an increased use of associated observations for operational modern low-latency numerical weather prediction (NWP) models, which assimilate GNSS-derived zenith total delay (ZTD) estimates. The development of NWP models with faster assimilation cycles, e.g., 1-h assimilation cycle in the rapid update cycle NWP model, has increased the interest of the meteorological community toward sub-hour ZTD estimates. The suitability of real-time ZTD estimates obtained from three different precise point positioning software packages has been assessed by comparing them with the state-of-the-art IGS final troposphere product as well as collocated radiosonde (RS) observations. The ZTD estimates obtained by BNC2.7 show a mean bias of 0.21 cm, and those obtained by the G-Nut/Tefnut software library show a mean bias of 1.09 cm to the IGS final tro-posphere product. In comparison with the RS-based ZTD, the BNC2.7 solutions show mean biases between 1 and 2 cm, whereas the G-Nut/Tefnut solutions show mean biases between 2 and 3 cm with the RS-based ZTD, and the ambiguity float and ambiguity fixed solutions obtained by PPP-Wizard have mean biases between 6 and 7 cm with the references. The large biases in the time series from PPP-Wizard are due to the fact that this software has been developed for kinematic applications and hence does not apply receiver antenna eccentricity and phase center offset (PCO) corrections on the observations. Application of the eccentricity and PCO corrections to the a priori coordinates has resulted in a 66 % reduction of bias in the PPP-Wizard solutions. The biases are found to be stable over the whole period of the comparison, which are criteria (rather than the magnitude of the bias) for the suitability of ZTD estimates for use in NWP nowcasting. A millimeter-level impact on the ZTD estimates has also been observed in relation to ambiguity resolution. As a result of a comparison with the established user requirements for NWP nowcasting, it was found that both the G-Nut/Tefnut solutions and one of the BNC2.7 solutions meet the threshold requirements, whereas one of the BNC2.7 solution and both the PPP-Wizard solutions currently exceed this threshold.
The use of observations from Global Navigation Satellite Systems (GNSS) in operational meteorology is increasing worldwide due to the continuous evolution of GNSS. The assimilation of near real-time (NRT) GNSS-derived zenith total delay... more
The use of observations from Global Navigation Satellite Systems (GNSS) in operational meteorology is increasing worldwide due to the continuous evolution of GNSS. The assimilation of near real-time (NRT) GNSS-derived zenith total delay (ZTD) estimates into local, regional and global scale numerical weather prediction (NWP) models is now in operation at a number of meteorological institutions. The development of NWP models with high update cycles for nowcasting and monitoring of extreme weather events in recent years, requires the estimation of ZTD with minimal latencies, i.e. from 5 to 10 minutes, while maintaining an adequate level of accuracy for these. The availability of real-time (RT) observations and products from the IGS RT service and associated analysis centers make it possible to compute precise point positioning (PPP) solutions in RT, which provide ZTD along with position estimates. This study presents a comparison of the RT ZTD estimates from three different PPP software packages (G-Nut/Tefnut, BNC2.7 and PPP-Wizard) to the state-of-the-art IGS Final Troposphere Product employing PPP in the Bernese GPS Software. Overall, the ZTD time series obtained by the software packages agree fairly well with the estimates following the variations of the other solutions, but showing various biases with the reference. After correction of these the RMS differences are at the order of 0.01 m. The application of PPP ambiguity resolution in one solution or the use of different RT product streams shows little impact on the ZTD estimates. Discussion and Conclusions The RT PPP ZTD estimates from three different software packages were compared using the IGS Final Troposphere Product as reference. In terms of standard deviation, it was seen that the solution from the G-Nut/Tefnut software library has the best agreement with the reference. After G-Nut/Tefnut solutions, the solutions from BNC2.7 are the next closest to the reference. Among the BNC2.7 solutions, a lower bias has been found for the solution computed using the correction stream containing Kalman Filter combination (IGS02) rather than the one computed using a single epoch solution correction stream (IGS01). The ambiguity float solution from the PPP-Wizard has the largest bias with the reference because of the fact that it currently does not apply corrections for receiver antenna phase centre offsets during processing. Integer ambiguity resolution using the PPP-Wizard seems to have a millimeter level effect on the RT PPP ZTD estimates. The RT PPP ZTD solutions were compared to the established user requirements for nowcasting by using RMS bias to IGFT as a measure of relative accuracy. It was seen that GN01, GN02, GN91 and BN02 fulfill the threshold requirements on ZTD accuracy whereas BN01, and PWFL (and PWFX) exceed this threshold.