Comparative analysis of real-time precise point positioning zenith total delay estimates

Abstract

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 troposphere 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 PPPWizard solutions currently exceed this threshold.

Generation of real‐time mode high‐resolution water vapor fields from GPS observations

“…About 82% of solutions show differences smaller than 15 mm with 73% below 12 mm. The RMS difference is 12.5 mm, commensurate with the spatial RMS difference and further indicating an RTPPP ZTD precision of about 1 cm, which is commensurate with previous real‐time studies [e.g., Li et al ., ; Ahmed et al ., ].…”

An evaluation of real‐time troposphere estimation based on GNSS Precise Point Positioning

“…Since the PPP-WIZARD has been mainly developed for RT kinematic positioning, the observation model applied in the software is not accurate enough to fulfill the accuracy requirements of meteorological applications. Ahmed et al [2016] highlighted this already during a comparison of free RT software available for GPS meteorology. To conduct our research, several modifications were implemented in the source code by the authors to improve the performance.…”

“…Ahmed et al . [] highlighted this already during a comparison of free RT software available for GPS meteorology. To conduct our research, several modifications were implemented in the source code by the authors to improve the performance.…”

“…Under these circumstances, several analyses of operational RT retrieval of ZTD using PPP based on GPS observations have been conducted. Analysis results based on actual GPS RT streams and IGS RT products revealed that the PWV estimates with an accuracy of better than 3 mm can be obtained, which implies that the method is complementary to current atmospheric sounding systems [ Ahmed et al ., ; Dousa and Vaclavovic , ; Li et al ., ; Yuan et al ., ].…”

Atmospheric opacity estimation based on IWV derived from GNSS observations for VLBI applications

“…The second method is time consuming and awkward in practice. The solution of the problem could be the use of GNSS measurements, which are relatively cheap, the processing methods are known quite well, and it is possible to estimate parameters even in real time (Ahmed et al 2016). As was mentioned above, using GNSS observations, it is possible to obtain IWV, which conveniently determines the quantity of atmospheric water vapor scaled by the density of water.…”