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Detecting offsets in GPS time series: first results from the detection of offsets in GPS experiment
journal contribution
posted on 2023-05-17, 21:45 authored by Gazeaux, J, Williams, S, Matt KingMatt King, Bos, M, Dach, R, Deo, M, Moore, AW, Ostini, L, Petrie, E, Roggero, M, Teferle, FN, Olivares, G, Webb, FHThe accuracy of Global Positioning System (GPS) time series is degraded by the presence of offsets. To assess the effectiveness of methods that detect and remove these offsets, we designed and managed the Detection of Offsets in GPS Experiment. We simulated time series that mimicked realistic GPS data consisting of a velocity component, offsets, white and flicker noises (1/f spectrum noises) composed in an additive model. The data set was made available to the GPS analysis community without revealing the offsets, and several groups conducted blind tests with a range of detection approaches. The results show that, at present, manual methods (where offsets are hand picked) almost always give better results than automated or semi-automated methods (two automated methods give quite similar velocity bias as the best manual solutions). For instance, the fifth percentile range (5% to 95%) in velocity bias for automated approaches is equal to 4.2 mm/year (most commonly ±0.4 mm/yr from the truth), whereas it is equal to 1.8 mm/yr for the manual solutions (most commonly 0.2 mm/yr from the truth). The magnitude of offsets detectable by manual solutions is smaller than for automated solutions, with the smallest detectable offset for the best manual and automatic solutions equal to 5 mm and 8 mm, respectively. Assuming the simulated time series noise levels are representative of real GPS time series, robust geophysical interpretation of individual site velocities lower than 0.2-0.4 mm/yr is therefore certainly not robust, although a limit of nearer 1 mm/yr would be a more conservative choice. Further work to improve offset detection in GPS coordinates time series is required before we can routinely interpret sub-mm/yr velocities for single GPS stations.
Funding
Australian Research Council
History
Publication title
Journal of Geophysical Research B: Solid EarthVolume
118Issue
5Pagination
2397-2407ISSN
0148-0227Department/School
School of Geography, Planning and Spatial SciencesPublisher
American Geophysical UnionPlace of publication
2000 Florida Ave Nw, Washington, USA, Dc, 20009Rights statement
Copyright 2013 American Geophysical UnionRepository Status
- Restricted