InSAR‐Derived Horizontal Velocities in a Global Reference Frame

Interferometric Synthetic Aperture Radar is used to measure deformation rates over continents to constrain tectonic processes. The resulting velocity measurements are only relative, however, due to unknown integer ambiguities introduced during propagation of the signal through the atmosphere. These ambiguities mostly cancel when using spectral diversity to estimate along-track motion, allowing measurements to be made with respect to a global reference frame. Here, we calculate along-track velocities for a partial global data set of Sentinel-1 acquisitions and find good agreement with ITRF2014 plate motion model and measurements from GPS stations. We include corrections for solid-earth tides and gradients of ionospheric total electron content. Combining data from ascending and descending orbits we are able to estimate north and east velocities over 250 × 250 km areas and their accuracy of 4 and 23 mm/year, respectively. These “absolute” measurements can be particularly useful for global velocity and strain rate estimation where GNSS measurements are sparse.