The ADOP and PDOP: Two Complementary Diagnostics for GNSS Positioning
Publication: Journal of Surveying Engineering
Volume 146, Issue 2
Abstract
Ambiguity dilution of precision (ADOP) and position dilution of precision (PDOP) are two popular scalar-diagnostics used in Global Navigation Satellite System (GNSS) positioning. Where the ADOP is a predictor for carrier-phase ambiguity resolution performance, the PDOP is meant to predict the receiver-satellite geometry’s capability for precise positioning. We will show, however, that although the PDOP works well for code-based positioning, one has to exercise great care in using the PDOP for real-time kinematic (RTK) positioning. We show that the ADOP and PDOP have distinct behaviors, an important consequence of which is that one can have time periods with small PDOPs, and thus seemingly good geometry for precise positioning, but at the same time large ADOPs, thus showing that successful ambiguity resolution and therefore precise positioning will not be possible. Also, the reverse situation may occur, i.e., having large PDOPs with small ADOPs. In such a situation, the large PDOPs should not automatically lead to the conclusion of poor position performance, because the large gain that ambiguity resolution brings will often still make precise positioning possible. We will analyze and explain this complementary behavior of the PDOP and ADOP and demonstrate this both analytically and empirically. For this analysis we use real Global Positioning System (GPS) single- and multifrequency signals and GPS/Quasi-Zenith Satellite System (QZSS), GPS/Navigation with Indian Constellation (NAVIC) L5 signals of two baselines located in Perth, Australia.
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Data Availability Statement
Some or all data, models, or code generated or used during the study are available in a repository or online in accordance with funder data retention policies (ftp://ftp.cddis.eosdis.nasa.gov/gnss/data/campaign/mgex/daily/rinex3/2018/brdm) [Combined broadcast ephemeris from the IGS MEGX campaign on CDDIS under MGEX (2018); see also Montenbruck et al. (2014, 2017)].
Some or all data, models, or code generated or used during the study are available from the corresponding author by request (1 Hz RINEX observation files of the tested stations on the test days).
Acknowledgments
We would like to thank Dr. Safoora Zaminpardaz for developing the GNSS Research Centre RTK software. The combined broadcast ephemeris was obtained from the IGS MGEX campaign on CDDIS. Peter J. G. Teunissen is the recipient of an Australian Research Council (ARC) Federation Fellowship (Project No. FF0883188).
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Published In
Journal of Surveying Engineering
Volume 146 • Issue 2 • May 2020
Copyright
©2020 American Society of Civil Engineers.
History
Received: May 8, 2019
Accepted: Nov 4, 2019
Published online: Feb 20, 2020
Published in print: May 1, 2020
Discussion open until: Jul 20, 2020
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