Ionospheric Mitigation for InSAR and Burst Overlap InSAR Using a Time-Series Approach

Ionospheric phase advance can be a significant nuisance, causing a bias in interferometric synthetic aperture radar (InSAR) measurements. Although methods have been developed to mitigate this effect, they are not always routinely applied when processing C-band SAR images, where the effect is generally expected to be small. However, the effect can be significant, especially when analyzing low deformation gradients over large areas using time-series analysis. Here, we present a time-series approach to ionospheric noise mitigation that improves on existing methods. We achieve this in three ways. First, we estimate the ionospheric contribution for each individual acquisition from multiple interferograms, which reduces noise. Second, we enhance the identification of unwrapping errors, which can bias the estimation. Third, we introduce a new filtering approach, which produces better results, particularly at image edges and areas with variable density of coherent measurements. Furthermore, our approach is applicable when estimating along-track motion in burst overlap areas. Our results show that applying the correction significantly improves velocity accuracy for both conventional line-of-sight (LOS) and burst overlap interferometry techniques. Consequently, applying ionospheric correction in InSAR workflows is essential for measuring long-term tectonic signals with mm/yr precision in the across- and along-track directions to constrain interseismic strain globally.