Long‐Wavelength Ionospheric Compensation of InSAR Time‐Series Based on Global Ionosphere Maps

Abstract Uncorrected long‐wavelength contributions remain a major limitation for interpreting InSAR time‐series over large areas (>100 km). Among them, the ionosphere can impact InSAR measurements across various timescales, potentially biasing secular velocity estimates. We use Global Ionosphere Maps (GIMs) to predict ionospheric effects for >15,000 Sentinel‐1 acquisitions in France, Tibet, and Central Andes. We evaluate GIM‐based corrections using phase ramps (planar functions fitted to interferograms) as proxies for long‐wavelength signals, enabling analysis of their temporal evolution. After correcting for solid Earth tides and oceanic tidal loading, GIM‐derived predictions show a strong temporal consistency with observed ramps, effectively capturing seasonal and multi‐year fluctuations with amplitudes of 0.2 mm/km. The highest‐resolution GIM also corrects part of the strong daily fluctuations of along‐track ramps observed on ascending tracks over equatorial regions. These corrections reduce ramp rate uncertainty and improve agreement with GNSS, paving the way toward direct InSAR measurement of tectonic plate motion.