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Impact of ocean tides loading on Precise Point Positioning based on FES2004 model

Kalita J. Z., Rzepecka Z.

Artificial Satellites : Journal of Planetary Geodesy

2015

Vol. 50, No. 2

77--89

Precise Point Positioning (PPP) technique as an absolute positioning method requires modeling of effects that influence observations. One of the effects is a displacement of the measurement location due to ocean mass gravitational attraction - ocean tides loading (OTL). The model recommended by the International Earth Rotation and Reference Systems Service (IERS) is FES2004. The paper focuses on impact of applying the particular OTL model on PPP processing. The analysis is based on processing of observations from 24 globally distributed permanent stations and time span of 50 days. The analysis bases on processing intervals from 1 to 24 hours. In addition, the amplitudes of the loads in Poland are evaluated. The OTL model is location dependent, thus the importance of applying this model depends on the location environment. As the PPP is an absolute method, the loads cumulate and transfer nearly directly to the positioning solution. Consequently, for short observation intervals and small loads the application of the model does not play an important role. For the analysed station with high amplitudes of the loads the relative and absolute improvement, of the solution was the highest for height component. By applying the model, the solution improved by 19% or 7.3 mm (as for RMS and 8 hour interval). The distinct improvement for convergence exists for vertical component and threshold below 5 cm. For Poland the vertical component loads were about 5 times smaller and the highest improvement for the analysed station was 3.7% for 4 hour interval and vertical component.

Evaluation of the possibility of using the predicted tropospheric delays in real time GNSS positioning

Kalita J. Z., Rzepecka Z., Krzan G.

Artificial Satellites : Journal of Planetary Geodesy

2014

Vol. 49, No. 4

179--189

Among many sources of errors that influence Global Navigation Satellite System (GNSS) observations, tropospheric delay is one of the most significant. It causes nonrefractive systematic bias in the observations on the level of several meters, depending on the atmospheric conditions. Tropospheric delay modelling plays an important role in precise positioning. The current models use numerical weather data for precise estimation of the parameters that are provided as a part of the Global Geodetic Observation System (GGOS). The purpose of this paper is to analyze the tropospheric data provided by the GGOS Atmosphere Service conducted by the Vienna University of Technology. There are predicted and final delay data available at the Service. In real time tasks, only the predicted values can be used. Thus it is very useful to study accuracy of the forecast delays. Comparison of data sets based on predicted and real weather models allows for conclusions concerning possibility of using the former for real time positioning applications. The predicted values of the dry tropospheric delay component, both zenith and mapped, can be safely used in real time PPP applications, but on the other hand, while using the wet predicted values, one should be very careful.