Azimuth Shift Estimation using Enhanced Spectral Diversity (EDS)

Sentinel-1 Azimuth Shift Estimation using ESD

This operator follows the S-1 Back Geocoding operator in the TOPS InSAR processing chain. The operator estimates a constant azimuth offset for the whole sub-swath using a Enhanced Spectral Diversity (ESD) method. The ESD approach exploits the data at the overlapped area of the adjacent bursts. The estimation is done for a number of windows in every overlapped area and the final azimuth offset is obtained by averaging all the estimations. 

The estimated azimuth shifts (overall shift for the whole sub-swath and shifts estimated for all windows in the overlapped areas) are saved in both the metadata of the output product and in an ASCII file with reference acquisition date and "_azimuth_shift" in the file name. The file can be found at user's \.snap\var\log folder. 

User can review the azimuth shifts estimated for all sub-swathes and decide which shift value will be used in the azimuth shift correction. To perform the azimuth correction, user can run the S-1 Enhanced Spectral Diversity operator with the user selected azimuth shift value. 

Generally users do not need to run this operator if they do not need to review the azimuth shift values. They can run the S-1 Enhanced Spectral Diversity operator directly where the azimuth shift is estimated using EDS and used directly in the azimuth shift correction. However, there are some cases where data in one sub-swath is corrupted and cannot be used in the azimuth shift estimation. In this case, users can use the azimuth shift estimated for other sub-swath in the correction of current sub-swath.

Input

• The input to this operator is the resulting product from the S-1 Back Geocoding operator. It is the co-registered reference and secondary images for the same sub-swath and same polarization (e.g. IW1 - VV).

Output

• The output product of the operator is the same as the input product except that the metadata has been updated with the estimated azimuth shifts.

Parameters Used

• Coherence Threshold for Outlier Removal: Pixels with coherence higher than the threshold are used in azimuth shift estimation.
  
• Number of Windows Per Overlap for ESD: The number of windows for azimuth shift estimation for each overlap area.