Enhanced Spectral Diversity

Sentinel-1 Enhanced Spectral Diversity

This operator follows the Backgeocoding operator in the TOPS InSAR processing chain. It first estimates a constant range offset for the whole sub-swath of the split S-1 SLC image using incoherent cross-correlation. The estimation is done for each burst using a small block of data in the center of the burst. The estimates from all bursts are then averaged to get the final constant range offset for the whole image.

The operator then 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 range and azimuth shifts are saved in the metadata of the output product. The ESD estimations for all windows and all overlaps are saved in and ASCII file with master and slave acquisition dates and "_azimuth_shift" in the file name. The file can be found at user's \.snap\var\log folder.

Finally, the operator performs range and azimuth corrections for every burst using the range and azimuth offsets estimated above with a phase ramp method in frequency domain.

When using ESD estimations read from ASCII files that were saved previously, an average is taken of all the estimates from the subswaths selected by the user. E.g., if the user selects IW1 and IW3, then one average is taken of the estimates from both IW1 and IW3.

Input

• The input to this operator is the resulting product from the Backgeocoding operator. It is the co-registered master and slave images for the same sub-swath and same polarization (e.g. IW1 - VV).
  

Output

• The output of the operator are the co-registered master and slave bands in I/Q format with the slave bands shifted by a small amount in range and azimuth directions.
  

Parameters Used

• Registration Window Width: Width of the sub-set of image used for cross-correlation.
  
• Registration Window Height: Height of the sub-set of image used for cross-correlation. Larger window generally implies accurate estimation of the range shift and also means larger memory and longer processing time.
• Search Window Accuracy in Azimuth Direction: The search accuracy in azimuth direction for the maximum correlation. The search window height is 2*Acc.
• Search Window Accuracy in Range Direction: The search accuracy in range direction for the maximum correlation. The search window width is 2*Acc. .
• Window Oversampling Factor: The oversampling factor for the search window. The larger the factor, the better the achievable accuracy, and the larger the computation cost.
  
• Cross-Correlation Threshold: Threshold for normalized cross-correlation value. If the cross-correlation value is greater than the threshold, then the estimated range offset is considered valid, otherwise invalid.
• Coherence Threshold for Outlier Removal:
  
• Number of Windows Per Overlap for ESD: The number of windows for azimuth offset estimation using ESD for each overlap area.
• Use User supplied shifts: If the checkbox is selected, then user supplied azimuth and range offsets will be used in shifting the image. For azimuth offsets, user can enter the shift value to be used, or check the box(es) to read the ESD estimations saved in ASCII files (assumed to be located in user's \.snap\var\log folder). No cross-correlation or ESD will be performed to estimate the offsets.
• The overall azimuth shift in pixels: The user provided azimuth offset in pixels.
  
• The overall range shift in pixels: The user provided range offset in pixels.