Quantitative analysis of geophysical sources of common mode component in CMONOC GPS coordinate time series

Common mode component (CMC) commonly exists in GPS coordinate time series, and its sources are still under investigation. It is challenging to quantify sources of CMC. This paper explores the sources of CMC and geophysical effects, including environmental loading and thermal expansion, on the Crustal Movement Observation Network of China (CMONOC) GPS coordinate time series. The CMCs of CMONOC time series are calculated using a correlation weighted stacking filtering method both before and after applying environmental loading and thermal expansion corrections, and the spectral characteristics of the CMC and the effects of these two geophysical factors on the CMC of CMONOC coordinate time series are then analyzed. The results indicate that environmental loading mainly affects the vertical component of the CMC, and it is not significant for the horizontal components. The reduction of the root mean square (RMS) of the CMC can be up to 1.5 mm in the vertical component and is less than 0.2 mm in the horizontal components. However, the effect of thermal expansion is not significant. The average RMS variation caused by thermal expansion correction of the CMC is less than 0.1 mm. The correlation coefficients are used as indicators of the CMC variation. The results show that the vertical coefficients generally decreased by an average of 28.8% after applying environmental loading correction, which indicates that the CMC is reduced by the environmental loading correction. In conclusion, approximately 20% reduction of the RMS of CMC by the environmental loading correction indicates that environmental loading is one of the main potential sources of the CMC in the vertical component and that thermal expansion may not be a major source of CMC. The results help explain the sources of CMC and can be used to improve the signal-to-noise ratio of GPS data.