Abstract
Interferometric Synthetic Aperture Radar (InSAR) is used to measure
deformation rates over whole continents to constrain tectonic processes.
The resulting velocity measurements are only relative, due to unknown
integer ambiguities introduced during propagation of the signal through
the atmosphere. However, 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 dataset of Sentinel-1
acquisitions and find good agreement with ITRF2014 model values. We
include corrections for solid-earth tides and gradients of ionospheric
total electron content. By combining data from ascending and descending
orbits we are able to estimate north and east velocities with average
precision of 4 and 20 mm/year, respectively. Although we have calculated
these over large 250x250 km areas, such measurements can also be made at
much higher resolution, albeit with lower accuracy. These “absolute”
measurements can be particularly useful for global velocity and strain
rate estimation, where GNSS measurements are sparse.