Spatiotemporal Ocean Tidal Loading in InSAR Measurements Determined by Kinematic PPP Solutions of a Regional GPS Network

Abstract

The coastal crustal deformation caused by ocean tidal loading (OTL) varies spatially and temporally, and this spatiotemporal variation in satellite-based interferometric synthetic aperture radar (InSAR) measurements needs to be determined. In this paper, we propose a spatiotemporal modeling method to estimate the OTL displacements in InSAR measurements using the kinematic precise point positioning (PPP) solutions of a regional GPS network. We tested the method through an experiment using 25 Sentinel-1B images and long-term observations of 172 GPS reference sites from Southern California. The experimental results suggest that there are significant OTL and solid Earth tide effects in the differential InSAR interferogram, which is greater than 40 mm. We find that the spatial characteristics of OTL variations can be expressed as a high-order polynomial in the two variables of latitude and longitude, and the spatiotemporally modeled PPP tidal estimates of the high-density GPS sites can provide high precision OTL correction for all the pixels in the interferogram. In the last part of the study, we show that the spatial large-scale signals in the differential interferograms of Sentinel-1B data are mainly atmospheric delay, solid Earth tidal and OTL effect, and demonstrate the importance of the tidal correction in the InSAR measurements.

Evaluation of Tidal Effect in Long-Strip DInSAR Measurements Based on GPS Network and Tidal Models

“…We evaluated the ground tidal displacement in the long-strip differential interferogram based on the tidal estimation of the GPS continuous reference station network and the tidal model. For inland areas more than 200 km away from the coastline of the west coast of the U.S., the error produced by bilinear ramp fitting is much less than in coastal areas, which has limited influence on the studies of InSAR ground deformation monitoring; For most coastal areas, there is little difference between the traditional ocean tide model and PPP tidal displacements, and previous studies have proved the OTL displacements in the InSAR measurements can be corrected based on a global ocean tide model [12,13]. However, Figure 4 and Abbaszadeh et al both indicated that in some localized coastal areas, such as Area A, the maximum StdDev differences between the tidal constituents' displacement time series of recent global ocean tide models are 1~2 mm [22], which may be introduced tidal displacement residuals into the OTL correction of the InSAR ground deformation measurements.…”

“…The global OTL displacements are usually calculated using an ocean tidal model-based loading Green's function method. Taking the FES2014b model as an example, the up (U), north (N) and east (E) OTL displacements d OTL n,p of point p with an interval of 300 s in the year 2019 can be obtained by using the ocean tidal model-based loading Green function method, and the variation of the OTL displacements in three-dimension is evaluated by the standard deviation (StdDev) S OTL p , which can be expressed as [12]:…”

“…Without considering the atmospheric delay and other largescale errors, DiCaprio et al simulated the OTL displacements in the ERS and ENVISAT data based on the FES2004 ocean tidal model, demonstrating the importance of correcting the nonlinear OTL displacement in a DInSAR interferogram [9,10]. If atmospheric delay and other large-scale errors are considered, they need to be settled by external correction data or two-dimensional image separation methods, which are limited to the accuracy of atmospheric delay and other large-scale error correction [11,12]. Yu et al simulated the OTL displacement in global Sentinel-1 data based on the FES2014b model and analysed the comprehensive impact of the OTL effect and atmospheric delay error [13].…”