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 article, 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.
Highlights
T HE Interferometric synthetic aperture radar (InSAR) is a powerful tool for mapping the Earth’s ground displacements, and the Sentinel-1 measurements in coastal areas usually contain tectonic deformation, atmospheric delay, the ocean tidal loading (OTL) effect, solid Earth tidal (SET) effect, orbitalManuscript received March 28, 2020; revised May 20, 2020; accepted May 31, 2020
The OTL effect is the response of the solid Earth to ocean mass redistribution due to the gravitational force changes, its gradient nonlinearly decreases from cm/100-km scale in the coastal area to mm/100-km scale in the area 200 km away from the coast [4]–[6]
The topography phase was removed using the shuttle radar topography mission-1 (SRTM-1) digital elevation model (DEM), and the minimum cost flow (MCF) method was used for the phase unwrapping
Summary
T HE Interferometric synthetic aperture radar (InSAR) is a powerful tool for mapping the Earth’s ground displacements, and the Sentinel-1 measurements in coastal areas usually contain tectonic deformation, atmospheric delay, the ocean tidal loading (OTL) effect, solid Earth tidal (SET) effect, orbital. The residual signals of the atmospheric delay and orbital error in the differential InSAR (DInSAR) interferogram may introduce the spatial large-scale error in the determination of the OTL displacements, so we used the ocean tide models and kinematic precise point positioning (PPP) tidal estimates of a regional GPS network to analyze the temporal and spatial variation of the OTL effect in the InSAR measurements. Tide models such as TPXO8, EOT11A, DTU10, FES2014b, and so on, are established by assimilating satellite altimeter or geodetic tide station data into a hydrodynamic model [10]–[12]. We further consider the selection of the kernel function based on the spatial variation of the phasors of the tide model and the PPP tidal estimates
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