Identification of significant periodicities in daily GPS time series using least-squares spectral analysis
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ORIGINAL PAPER
Identification of significant periodicities in daily GPS time series using least-squares spectral analysis Fereydoun Nobakht-Ersi1 · Sonja Gamse2 · Mohammad A. Sharifi3
Received: 14 October 2015 / Accepted: 7 April 2016 © Saudi Society for Geosciences 2016
Abstract Coordinate time series, generated from continuous observations at permanent GPS stations, expose systematic variations. In a site motion model, which is used in geodynamic tasks for computation of velocities (rates and directions) of GPS stations, unknown parameters of the linear rate, annual, semi-annual periodicities, and offsets are estimated using least-squares technique. In our contribution, we analyzed residual time series, which still expose periodical variations. The statistically significant frequencies were extracted using least-squares spectral analysis and additional sinusoidal terms were subsequently added to the basic site motion model. By iterative procedure, the residuals decrease and the coordinate time series render a random noise process. By decreasing root mean square value, we
Electronic supplementary material The online version of this article (doi: 10.1007/s12517-016-2468-9) contains supplementary material, which is available to authorized users. Fereydoun Nobakht-Ersi
[email protected] 1
Department of Surveying and Geomatics Engineering, College of Engineering, University of Tehran, Kargare Shomali St., Tehran 1439957131, Iran
2
Unit for Surveying and Geoinformation, Faculty of Engineering Science, University of Innsbruck, Technikerstr. 13, Innsbruck 6020, Austria
3
Department of Surveying and Geomatics Engineering, Research Institute of Geoinformation Technology (RIGT), College of Engineering, University of Tehran, Kargare Shomali St., Tehran 1439957131, Iran
can conclude that the parameter estimates are determined with more realistic uncertainties. The results were analyzed for the coordinate time series of 125 GPS stations of SCIGN permanent network that were active during January 1, 2000 to December 30, 2007. Keywords GPS coordinate time series · Least-squares spectral analysis · Residual analysis · Site motion model · Time series analysis
Introduction Geodetic methods (terrestrial measurement systems such as tachymeters and leveling, Global Navigation Satellite Systems (GNSS)/Global Positioning System (GPS), terrestrial or airborne laser scanners, or other techniques of remote sensing, such as Interferometric synthetic aperture radar (InSAR)) can be used to investigate the local or regional crustal deformations. Especially methods of space geodetic techniques of GPS are nowadays standardized procedures for continuous monitoring of ground motions and to study geophysical phenomena of plate tectonics. The obtained measurements from permanent ground-based reference sites of continuous GPS networks (CGPS) provide position/coordinate time series, which are influenced by several disturbances. The reasons for positional offsets, data gaps, and errors in GPS coordinate time series, which should be analyze
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