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Published October 10, 2017 | public
Journal Article

InSAR Time-Series Estimation of the Ionospheric Phase Delay: An Extension of the Split Range-Spectrum Technique


Repeat pass interferometric synthetic aperture radar (InSAR) observations may be significantly impacted by the propagation delay of the microwave signal through the ionosphere, which is commonly referred to as ionospheric delay. The dispersive character of the ionosphere at microwave frequencies allows one to estimate the ionospheric delay from InSAR data through a split range-spectrum technique. Here, we extend the existing split range-spectrum technique to InSAR time-series. We present an algorithm for estimating a time-series of ionospheric phase delay that is useful for correcting InSAR time-series of ground surface displacement or for evaluating the spatial and temporal variations of the ionosphere's total electron content (TEC). Experimental results from stacks of L-band SAR data acquired by the ALOS-1 Japanese satellite show significant ionospheric phase delay equivalent to 2 m of the temporal variation of InSAR time-series along 445 km in Chile, a region at low latitudes where large TEC variations are common. The observed delay is significantly smaller, with a maximum of 10 cm over 160 km, in California. The estimation and correction of ionospheric delay reduces the temporal variation of the InSAR time-series to centimeter levels in Chile. The ionospheric delay correction of the InSAR time-series reveals earthquake-induced ground displacement, which otherwise could not be detected. A comparison with independent GPS time-series demonstrates an order of magnitude reduction in the root mean square difference between GPS and InSAR after correcting for ionospheric delay. The results show that the presented algorithm significantly improves the accuracy of InSAR time-series and should become a routine component of InSAR time-series analysis.

Additional Information

© 2017 IEEE. Manuscript received February 20, 2017; revised May 2, 2017; accepted June 13, 2017. Date of publication July 21, 2017; date of current version September 25, 2017. The work of H. Fattahi and M. Simons was supported by the National Aeronautics and Space Administration under Grant NNX14AH80G and Grant NNX16AK58G. (Corresponding author: Heresh Fattahi.) The authors would like to thank the Alaska Satellite Facility and the Japanese Aerospace Exploration Agency for providing the ALOS-1 data, P. Rosen from the Jet Propulsion Laboratory, NASA, F. Meyer from the University of Alaska–Fairbanks, and G. Gomba from the German Aerospace Center for helpful discussions on ionospheric phase delay in InSAR data. U.S. Government sponsorship acknowledged.

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