Modelling the elevation-dependent seasonal amplitude of tropospheric delays in GPS time-series using DInSAR and meteorological data

A dominant source of error in space-based geodesy is the tropospheric delay, which results in excess path length of the signal as it passes through the neutral atmosphere. Many studies have addressed the use of global weather models and local meteorological observations to model the effects of this error in Global Positioning System (GPS) and Differential Interferometric Synthetic Aperture Radar (DInSAR) data. However, modelling of zenith tropospheric delays (ZTDs) errors in the GPS data, particularly in the areas of strong topographic relief, is highly problematic because ZTD estimates cannot be captured by low resolution weather models and often it is not possible to find a nearby weather station for every GPS station. In this paper, we use DInSAR data with high spatial and temporal resolution from the volcanic island of Hawaii to estimate the seasonal amplitudes of ZTD signals, which then are used to remove this error from GPS data. Here we observe the seasonal amplitude for more than one million DInSAR pixels for the time period between 2014 and 2017 and propose a best-fitting elevation-dependent model. This model is an integration of the exponential refractivity function and is linked to the observations from a radiosonde station and a weather station. It estimates seasonal amplitudes ranging from 0.2 cm at the highest elevations to 5.6 cm at the lower elevations, increasing exponentially from the DInSAR reference elevation. To demonstrate the potential of this model for correction of GPS data, we compare the modelled seasonal amplitude to the observed seasonal amplitudes of the variation of the local ZTD, computed from the Canadian Spatial Reference System-precise point positioning (CSRS-PPP) online application, for 21 GPS stations distributed throughout the island. Our results show that this model provides results with root-mean-square error (rmse) values of less than 1 cm for the majority of GPS stations. The computed rmse of the residuals between the modelled seasonal signal and the high frequency variations of the ZTD signal at each station relative to the reference GPS station, here PUKA, range between 0.7 and 4.1 cm. These estimated values show good agreement with those computed for the rmse of the residuals computed between the observed seasonal signal and the high frequency variations of ZTD, ranging from zero to 0.3 cm. This confirms the potential of the proposed DInSAR model to accurately estimate the seasonal variation of ZTDs at GPS stations at any arbitrary altitude with respect to the reference station.This research is supported by the NSERC Collaborative Research and Development (CRD) grant, ’Real-time ground motion tools for seismic hazard management’. The work of KFT was supported by an NSERC Discovery Grant.Peer reviewe