Abstract
Kinematic analysis of Global Navigation Satellite System (GNSS) data is useful for the extraction of crustal deformation phenomena occurring over short timescales ranging from seconds to 1 day, such as coseismic and postseismic deformation following large earthquakes. However, a fundamental challenge in kinematic GNSS analysis is to separate unknown parameters, such as site coordinate and tropospheric parameters, due to the strong correlation between them. In this study, we assessed the spatial and temporal characteristics of process noise for unknown tropospheric parameters such as zenith wet tropospheric delay and tropospheric gradient by means of kinematic precise point positioning analysis using Kalman filtering across the Japanese nationwide continuous GNSS network. We estimated kinematic site coordinate time series under different process noise combinations of zenith wet tropospheric delay and tropospheric gradient. The spatial distribution of the optimum process noise value for the zenith wet tropospheric parameter with vertical site coordinate time series clearly showed regional characteristics. In comparison with the wet tropospheric parameter, the spatial characteristics of the tropospheric gradient parameter are less well defined within the scale of the GNSS network. The temporal characteristics of the optimum process noise parameters for each site coordinate component at specific sites indicated a clear annual pattern in the tropospheric gradient parameter for the horizontal components. Finally, we assessed the effects on the kinematic GNSS site coordinate time series of optimizing tropospheric parameter process noise. Compared with recommended process noise values from previous studies, the use of estimated “common” optimum process noise values improved the standard deviation of coordinate time series for the majority of stations. These results clearly indicate that the use of appropriate process noise values is important for kinematic GNSS analysis.
Highlights
The application of a Global Navigation Satellite System (GNSS) to the understanding of crustal deformation has significant advantages
We initially focus on the spatial distribution of the optimum parameter settings between zenith wet delay (ZWD) and tropospheric gradient across the Japanese nationwide GNSS network, which comprises more than 1300 stations
The results clearly show a strong dependency between the tropospheric delay (TROP) and time series in the vertical coordinate component
Summary
The application of a Global Navigation Satellite System (GNSS) to the understanding of crustal deformation has significant advantages. Several studies deduced the rupture processes of large earthquakes from high sampling rate kinematic GNSS time series (e.g., Miyazaki et al 2004; Yokota et al 2009; Delouis et al 2010). Kinematic GNSS analysis has been used for real-time estimation of the magnitude and fault expansion of large earthquakes (e.g., Ohta et al 2012, 2015; Melgar et al 2013, 2015; Melgar and Bock 2013; Kawamoto et al 2016). These previous studies mainly focused on the coseismic time period. Kinematic GNSS time series usually show large disturbances in the lower frequency band (e.g., Genrich and Bock 2006), due to the difficulty of strict separation between the coordinate parameters and other unknown parameters, such as the tropospheric parameters
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