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Errors in the satellite orbits are considered to be a limitation for Interferometric Synthetic Aperture Radar (InSAR) time-series techniques to accurately measure long-wavelength (>50 km) ground displacements. Here we examine how orbital errors propagate into relative InSAR line-of-sight velocity fields and evaluate the contribution of orbital errors to the InSAR uncertainty. We express the InSAR uncertainty due to the orbital errors in terms of the standard deviations of the velocity gradients in range and azimuth directions (range and azimuth uncertainties). The range uncertainty depends on the magnitude of the orbital errors, the number and time span of acquisitions. Using reported orbital uncertainties we find range uncertainties of less than 1.5 mm yr⁻¹ 100 km⁻¹ for ERS, less than 0.5 mm yr⁻¹ 100 km⁻¹ for Envisat and ∼0.2 mm yr⁻¹ 100 km⁻¹ for TerraSAR-X and Sentinel-1. Under a conservative …