Accounting for Atmospheric Delays in InSAR Data in a Search for Long-Wavelength Deformation in South America

InSAR has been successfully used to observe the deformation of the Earth´s surface from many processes, but mostly dealing with relatively large signals (>;1 cm) over short wavelengths (<; 100 km). We use interferometric synthetic aperture radar (InSAR) data from two orbital tracks in northern Chile to study the feasibility of imaging the broad interseismic ground deformation signal from the Nazca Plate subduction. In order to measure ~1.5 cm/year of ground motion across ~1000 km of satellite track length due to interseismic loading of the subduction interface, the atmospheric contribution cannot be ignored. We attempt to remove the atmospheric signal using global weather models and by estimating atmospheric parameters directly from the InSAR data. Due to the poor temporal and spatial resolutions of the weather model, this method fails to produce reliable results. The empirical model reduces the phase variance in the interferograms but leaves a residual signal that continues to mask the interseismic signal, which demonstrates the importance of carefully applying corrections to the data as they can significantly affect any interpretation that is based on the corrected observations. Although the methods presented here are not suited for removing all atmospheric path delays, this paper does provide suggestions about improvements that can be made to corrective techniques. Methods that should be further developed are the following: 1) corrections with independent and direct observations of atmospheric properties, e.g., continuous GPS or satellite observations (e.g., the MERIS sensor); 2) improvements using empirical corrections, either in conjunction with a deformation model or constrained by real atmospheric structures; and 3) further work with high resolution and improved weather models.