Back Geocoding

Sentinel-1 Back Geocoding

This operator co-registers two S-1 SLC split products (master and slave) of the same sub-swath using the orbits of the two products and a Digital Elevation Model (DEM).

In resampling the slave images into master frame, deramp and demodulation are performed first to the slave image, then the truncated-sinc interpolation is performed. Finally, the reramp and remodulation are applied to the interpolated slave image.

Input

• Before running this operator, user should first run S-1 TOPS Split operator to both master and slave products to get the same sub-swath and same polarization data for co-registration (e.g. IW1 - VV).
  
• The user should run Apply Orbit File to correct the orbits in both the split products with the Sentinel Precise (or Restitude) orbit files. This step can be skipped if no precise or restitude orbit file is available. Otherwise this step is always recommended in order to achieve better co-registration result.
  

Output

• The output of the operator are the co-registered master and slave bands in I/Q format.
  

Parameters Used

• Digital Elevation Model: The DEM type. Currently the following DEMs are supported
  
• ACE2_5min
• ACE30
• ASTER 1sec GDEM
  
• GETASSE30
• SRTM 1Sec Grid
• SRTM 3Sec
• user provided external DEM file
  
• DEM Resampling Method: Interpolation method for obtaining elevation values from the original DEM file. The following interpolation methods are available
• nearest neighbour
• bi-linear
• cubic convolution
• 5-points bi-sinc
• 11-points bi-sinc
• 21-points bi-sinc
• bi-cubic
  
• Resampling Type: Interpolation methods for obtaining pixel values from the source image. The interpolation methods available are the same as listed above.
• Mask out areas with no elevation:  Checkbox indicating if areas without elevation should be masked out from co-registration. It is recommended to select this checkbox to avoid artefacts along the coast in the co-registered images.
  
• Output Deramp and Demod Phase: Checkbox indicating if deramp and demodulation phases should be output as separated bands. This option is mostly for debugging purpose and not recommended for most users.