Offset Tracking

Offset Tracking Operator

The Offset Tracking operator estimates the movement of glacier surfaces between two SAR images in both slant-range and azimuth direction. It performs cross-correlation on selected GCP-patches in master and slave images, and computes glacier velocities based on the shift computed for each GCP. Finally the glacier velocity map is computed through interpolation of the velocities computed for the GCP grid.

Parameters Used

   The parameters used by the operator are as follows:
  1. Grid Azimuth Spacing: The GCP grid azimuth spacing in pixels.
  2. Grid Range Spacing: The GCP grid range spacing in pixels.
  3. Registration Window Width: The window width for cross-correlation.
  4. Registration Window Height: The window height for cross-correlation.
  5. Cross-Correlation Threshold: Threshold for normalized cross-correlation value. If the cross-correlation value is greater than the threshold, then the estimated offset is considered valid, otherwise invalid.
  6. Average Box Size: Size of sliding window for averaging offsets computed for GCPs.
  7. Max Velocity: The maximum allowed glacier velocity in meters per day. It is used in eliminating outliers.
  8. Radius for Hole Filling: It defines the size of the window for hole filling. For GCP that has no valid offset, a window with given radius centered at the GCP is defined. Offsets from valid GCPs within the window are used in interpolating the offset for the current GCP.