Abstract
Analysis of Global Positioning System (GPS) position time series and its common mode components (CMC) is very important for the investigation of GPS technique error, the evaluation of environmental loading effects, and the estimation of a realistic and unbiased GPS velocity field for geodynamic applications. In this paper, we homogeneously processed the daily observations of 231 Crustal Movement Observation Network of China (CMONOC) Continuous GPS stations to obtain their position time series. Then, we filtered out the CMC and evaluated its effects on the periodic signals and noise for the CMONOC time series. Results show that, with CMC filtering, peaks in the stacked power spectra can be reduced at draconitic harmonics up to the 14th, supporting the point that the draconitic signal is spatially correlated. With the colored noise suppressed by CMC filtering, the velocity uncertainty estimates for both of the two subnetworks, CMONOC-I (≈16.5 years) and CMONOC-II (≈4.6 years), are reduced significantly. However, the CMONOC-II stations obtain greater reduction ratios in velocity uncertainty estimates with average values of 33%, 38%, and 54% for the north, east, and up components. These results indicate that CMC filtering can suppress the colored noise amplitudes and improve the precision of velocity estimates. Therefore, a unified, realistic, and three-dimensional CMONOC GPS velocity field estimated with the consideration of colored noise is given. Furthermore, contributions of environmental loading to the vertical CMC are also investigated and discussed. We find that the vertical CMC are reduced at 224 of the 231 CMONOC stations and 170 of them are with a root mean square (RMS) reduction ratio of CMC larger than 10%, confirming that environmental loading is one of the sources of CMC for the CMONOC height time series.
Highlights
The Crustal Movement Observation Network of China (CMONOC) is an important scientific infrastructure in China, which initially contained 27 Continuous Global Positioning System (GPS) stations in 1999 and was extended to 260 GPS stations since 2011
Analyzing the GPS position time series of CMONOC is vital for unbiased velocity estimates, as well as realistic velocity uncertainty estimates, which is a necessity for appropriate interpretations of the above mentioned geophysical phenomena
Analyzing the GPS position time series of CMONOC, a long-running, continental-scale and high-density GPS network, can provide a wealth of information on the periodic signals, noise characteristics, and sources of the common mode component (CMC) for GPS position time series, which can be a reference for similar studies over other regions
Summary
The Crustal Movement Observation Network of China (CMONOC) is an important scientific infrastructure in China, which initially contained 27 Continuous Global Positioning System (GPS) stations in 1999 and was extended to 260 GPS stations since 2011. Previous studies have reported that periodic signals are present in GPS position time series, such as the seasonal signals [9], draconitic signal and its harmonics [10], spurious long-period signals caused by unmodeled short-period signals [11], and other periodic signals due to unknown reasons [12]. Abraha et al [17] reported that the draconitic signal is mostly from satellite-related effects with a non-zero contribution of site-specific errors. As the orbital errors and unmodeled geophysical tide loading effects are spatially correlated while the multipath effect is a site-specific error source, we will investigate the spatial correlation of the draconitic signal in this study so that its source can be more reliably speculated
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