气候变化领域集成服务门户

Coastal zone is one of the most complex and fragile natural ecological environments in the world. Synthetic Aperture Radar Interferometry (InSAR) techniques can provide vital information on surface topography and deformation in the ocean-land transition zones under the background of global human activities, climate warming and violent tectonic movements over subduction zones. Ocean tides cause a temporal variation of the ocean mass distribution and the associated load on the crust and produce time-varying deformations of the Earth that can reach 100 mm with a wavelength scale of 10(2) similar to 10(3) km and deformation gradients of mm level to cm level. This kind of non-tectonic signals will have a significant impact on InSAR precision deformation analysis (e. g. large-scale slow and non-steady tectonic deformation with small magnitude). In this study, we used various ocean tidal models to investigate the ocean tidal load (OTL) effects on wide-swath (WS) mode InSAR (e. g. ALOS-2 PALSAR-2 and Sentinel-1A) deformation monitoring in three typical coastal regions including China, Chile and Gulf of Alaska. We detailedly demonstrated the method of three-dimensional component estimation of OTL and differential OTL phase for WS InSAR and further discussed the differences of ocean tidal models in the estimation of OTL displacements. We find that (1) the magnitude of the OTL effects relates with the spatial range of the study regions, and (2) there are strong correlations between the OTL deformation gradient changes and costal topography. Therefore, traditional flat or curved surface fitting methods are difficult to effectively separate the tidal load displacement for the long wavelength deformation monitoring. It is thus highly recommended in this paper that they should be estimated and corrected carefully in interferometric processing, particularly when long wavelength crustal deformation is targeted. For long time series of deformation monitoring over a wide range of coastal zone (>100 km), if image acquisition time was not away from the astronomical tide and tidal changes in the peak time especially for those Sentinel SAR images with shorter temporal baselines (e. g. 12 days), one should consider how to effectively estimate and correct the OTL effects. Besides, InSAR OTL estimation should keep up to date with the latest global ocean models at high spatial resolution or region tidal models integrated with long-term tide gauge observation.