Analysing the Zenith Tropospheric Delay Estimates in On-line Precise Point Positioning (PPP) Services and PPP Software Packages.

Jorge Mendez Astudillo,Yu-Ting Tang,Lawrence Lau,Terry Moore

doi:10.3390/s18020580

Abstract

As Global Navigation Satellite System (GNSS) signals travel through the troposphere, a tropospheric delay occurs due to a change in the refractive index of the medium. The Precise Point Positioning (PPP) technique can achieve centimeter/millimeter positioning accuracy with only one GNSS receiver. The Zenith Tropospheric Delay (ZTD) is estimated alongside with the position unknowns in PPP. Estimated ZTD can be very useful for meteorological applications, an example is the estimation of water vapor content in the atmosphere from the estimated ZTD. PPP is implemented with different algorithms and models in online services and software packages. In this study, a performance assessment with analysis of ZTD estimates from three PPP online services and three software packages is presented. The main contribution of this paper is to show the accuracy of ZTD estimation achievable in PPP. The analysis also provides the GNSS users and researchers the insight of the processing algorithm dependence and impact on PPP ZTD estimation. Observation data of eight whole days from a total of nine International GNSS Service (IGS) tracking stations spread in the northern hemisphere, the equatorial region and the southern hemisphere is used in this analysis. The PPP ZTD estimates are compared with the ZTD obtained from the IGS tropospheric product of the same days. The estimates of two of the three online PPP services show good agreement (<1 cm) with the IGS ZTD values at the northern and southern hemisphere stations. The results also show that the online PPP services perform better than the selected PPP software packages at all stations.

Highlights

Global Navigation Satellite System (GNSS) data is widely used for positioning and navigation in mass-market and engineering applications [1] and for altitude determination [2], it can be used for monitoring the atmosphere
In order to assess the quality of the Zenith Tropospheric Delay (ZTD) estimates of the 6 Precise Point Positioning (PPP) software previously described, observation data from the 9 International GNSS Service (IGS) stations were processed with each of the software packages and the ZTD was estimated in kinematic mode
Every software used for the analysis presented in this study uses a similar strategy to estimate the Zenith Tropospheric Delay, which is using a model to estimate the hydrostatic slant delay, use a mapping function to estimate the delay in the zenith direction and estimate the wet delay as an unknown in the parameter estimation process typically done with an Extended Kalman Filter

Summary

Introduction

GNSS data is widely used for positioning and navigation in mass-market and engineering applications [1] and for altitude determination [2], it can be used for monitoring the atmosphere. An example of the use of GNSS data for applications other than positioning and navigation is the integration of the GNSS-derived Path Delay with microwave radiometer measurements to find a precise wet tropospheric correction for altimetric products [4]. Another use of GNSS data is the remote sensing of the atmosphere, where GNSS signals can be used. Other examples are the measurement of the amount of precipitable water in the atmosphere using GPS signals as in the experiment GPS/MET [6,7]

Methods

Results

Discussion

Conclusion