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Geodynamics Displacements

Precise geolocation and phase interpretation in SAR and InSAR applications require accounting not only for atmospheric effects but also for solid Earth deformations. These deformations arise from gravitational interactions and long-term tectonic motion, introducing displacements that can reach centimeters to decimeters—well within the sensitivity of modern SAR systems.

Corner Reflectors coordinates update

These motions causes Corner Reflectors to shift over time relative to their originally surveyed positions. As a result, their coordinates at the time of a SAR acquisition no longer match those measured during the survey. The displacement can be accurately accounted for by applying the ITRF2014 plate motion model and Solid Tides, updating the reflector position to the SAR product acquisition time.

Earth Solid Tides

Earth Solid Tides are periodic deformations of the Earth’s crust caused by the gravitational attraction of the Moon and the Sun. Unlike ocean tides, these affect the solid Earth itself, producing elastic displacements of the surface.

Key characteristics:

  • Vertical displacements up to ~30–40 cm
  • Horizontal displacements up to ~10 cm
  • Dominant periodicities:
    • Semi-diurnal (~12 hours)
    • Diurnal (~24 hours)

This package computes these effects using a Python wrapper of the original solid.for code by Dennis Milbert1, itself based on an implementation derived from the IERS Conventions (2003). These conventions provide internationally standardized models for Earth orientation and deformation, ensuring consistency with geodetic and geophysical reference frames.

Plate Tectonics (Secular Motion)

In addition to periodic tidal effects, the Earth’s crust undergoes long-term motion due to plate tectonics. This motion is generally linear over time and can be described using plate motion models such as ITRF2014.

Key characteristics:

  • Typical velocities: mm/year to cm/year
  • Direction and magnitude depend on tectonic plate location
  • Accumulates over time, leading to measurable displacement between acquisitions

The displacement is computed as:

\[ d(t) = v \cdot (t - t_0) \]

where \(v\) is the plate velocity vector from the ITRF2014 model and \(t_0\) is the location survey time.

  1. Dennis Milbert, Ph.D., Chief Geodesist, National Geodetic Survey, NOAA, (retired) https://geodesyworld.github.io/SOFTS/solid.htm ↩