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Horizontal Velocities in a Global Reference Frame Derived from Sentinel-1 Along-track Interferometry
  • Milan Lazecky,
  • Andrew Hooper,
  • Chris Rollins
Milan Lazecky
University of Leeds

Corresponding Author:m.lazecky@leeds.ac.uk

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Andrew Hooper
University of Leeds, COMET
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Chris Rollins
University of Leeds
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InSAR measurements of ground displacement are 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 (azimuth) velocities allowing measurements to be made with respect to a terrestrial reference frame. Here, we calculate along-track velocities for a partial global dataset of Sentinel-1 acquisitions as processed by the COMET LiCSAR system, and find good agreement with model values from ITRF2014 plate motion model. We include corrections for solid-Earth tides and gradients of ionospheric total electron content based on a moderate resolution model IRI2016. Application of tidal corrections improves the average velocity precision from 23 to 11 mm/yr. Ionospheric corrections, however, have significant effect only in near-equatorial regions. The median difference between along-track velocities and values predicted by ITRF2014 is 3 mm/yr. A preliminary study using reprocessed precise orbit determination products in a limited dataset shows significant improvement in both precision and accuracy. By combining data from ascending and descending orbits we are able to estimate north-south (N-S) and east-west (E-W) velocities with an average precision of 3 and 16 mm/yr, respectively. Although we have calculated these estimates over large 250 x 250 km areas, such measurements can also be made at much higher resolution, albeit with lower precision. These “absolute” measurements can be particularly useful for global velocity and strain rate estimation, where GNSS measurements are sparse. We will also investigate large-scale averages of across-track (range) pixel offsets, which are most sensitive to E-W and vertical displacements, and perform a comparison to a GNSS network in selected areas.