Tropospheric Delay Estimation for Pseudolite Positioning

Jianguo Jack Wang, Jinling Wang, David Sinclair, Hung Kyu Lee

Electronics and Telecommunications Research Institute (ETRI), Rep. of Korea.
QASCO Surveys Pty. Limited, 41 Boundary St. South Brisbane, Australi.
School of Surveying and Spatial Information Systems, The University of New South Wales, Sydney, NSW 2052, Australia.

DOI:                 

Abstract

Pseudolites, ground-based GPS signal transmitters, can significantly enhance the GPS satellite geometry or can even be an independent positioning system. However, as pseudolites are very close to the receivers, error effects are different from the traditional GPS and should be considered and modeled in a different way. Tropospheric delay is one of the largest error sources in pseudolite positioning, as pseudolite signalpropagates through the lower troposphere which is very difficult to be modeled due to spatial variations in atmosphere. The objective of this research is to analysepseudolite tropospheric delay modelling methods and to select the optimal tropospheric delay models for differentapplications. Several methods to estimate the tropospheric delay for pseudolite positioning are introduced and compared. One approach is to utilize single-differenced GPS tropospheric models. Another one is to compute the tropospheric delay as a function of the local refractivity along the pseudolite signal path. The ratio method used for Electronic Distance Measurement (EDM) can also be applied to estimate tropospheric delay. Experiments with simulation and real flight test data are conducted in this study to investigate the proposedmethods. The advantages and limitations of each method are analysed. The mode defined by RTCA and its modification are suitable for a low elevation and short range application, such as LAAS and local ground based applications. Models derived from single-differenced NMF and Saastamoinen models perform well in long range and high elevation but have a big bias in low elevation. And the model derived from the Hopfield model performs relatively well in all the range andelevation.

Keywords

Pseudolite, tropospheric delay, modelling

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Biberger R J.; Teuber A.; Pany T.; Hein G W. (2003): Development of an APL Error Model for Precision Approaches and Validation by Flight Experiments. In: ION (Editor), GPS/GNSS, Portland, OR, pp. 2308-2317.
[2]	Bouska C T J.; Raquet J F. (2003): Tropospheric Model Error Reduction in Pseudolite Based Positioning Systems, ION GPS/GNSS 2003, Portland OR, USA, pp. 390-298.
[3]	Fukushima S.; Yoshihara T.; Suga S. (2004): Evaluation of a Tropospheric Correction Model fpr Airport Pseudolite, ION GPS/GNSS 2004, Long beach CA, USA.
[4]	Hofmann-Wellenhof B.; Lichtenegger H.; Collins J. (2000): GPS Theory and Practice. Fifth revised edition. Springer- Verlag Wien, New York, 382 pp.
[5]	Lee H K.; Wang J.; Rizos C.; Park W (2003): Carrier phase processing issues for high accuracy integrated GPS/Pseudolite/INS systems, Proceedings of 11th IAIN World Congress, Berlin, Germany, paper 252.
[6]	Niell A E. (1996): Global mapping functions for the atmosphere delay at radio wavelengths. Journal of Geophysical Research, 101(B2): 3227-3246.
[7]	RTCA (2000): GNSS Based Precision Approach Local Area Augmentation System (LAAS)-Signal-in-Space Interface Control Document (ICD). RTCA/DO-246A, Radio Technical Commission for Aeronautics.
[8]	Rueger J M. (1996): Electronic Distance Measurement, An Introduction. Springer, 276 pp.