Assessing the degree of synchronization between geophysical records using the method of instantaneous phase differences

Abstract

Recovering geodetic parameters such as tropospheric delay and geodetic site positions and monitoring their variations in time has important applications for studying the processes of the dynamic earth. Geodetic position time series exhibit non-linear motions that are associated with seasonal signals caused by loading effects, and seismic deformation processes such as earthquakes etc. This implies that the fluctuations in the station coordinates and tropospheric parameters could be synchronized because they are driven by common underlying processes. In the analysis of space geodetic measurements, space geodetic solutions are often co-assessed in order to determine geophysical signals present in both parameters. The main objective of the current analysis is to determine the linkage between temporal structure of the zenith tropospheric delay and the geodetic station height coordinates fluctuations in the time-frequency-energy space. The temporal structures of the combined solution of the zenith tropospheric wet delay (ZWD) and the geodetic station height at the Hartebeesthoek geodetic station (HartRAO) have been studied. The oscillation patterns in these geophysical signals have been analysed by using the noiseassisted data analysis (NADA) methodology known as ensemble empirical mode decomposition (EEMD). The instantaneous phase differences among the associated modes of the intrinsic mode functions (IMFs) have been computed and used to assess the degree of synchronisation between the two series. The results showed that the ZWD and the HartRAO geodetic station height show modes that are temporally correlated and some of the IMF modes exhibit temporal structures that can be associated with both local and global forcing mechanisms.