Add S-1 TOPs Merge step to handle multiple subswaths

[loreabad6]

Currently, if multiple subswaths are detected to intersect the AOI, then we raise an error since this is not supported yet. The selection happens internally so if the AOI matches multiple IW then the pipeline will exit with an Error.

But what can be done to get around it? Options:

• Provide a different AOI?

For a good implementation see the Inferferometry ESA tutorial page 7.

TOPS Split
S-1 TOPS Split is applied to the data to select only those bursts which are required for the analysis. They are marked in blue in Figure 1. Currently, each Sub-Swath is processed separately. Note: If the area of interest covers several Sub-Swaths, they have to be merged with the S-1 TOPS Merge operator after the Sub-Swaths were debursted.

[loreabad6]

To implement this, we would need to:

• Restructure the workflow steps:
  - Set P1 to only extract bursts and subswaths
  - Merge P1 and P2 SNAP functions
  - 1. topsar_split, 2. apply_orbit_file, 3. back_geocoding,
  x. enhanced_spectral_diversity, 4. topsar_deburst,
  5. interferogram, 6. topsar_merge, 7. ...
• Modify stsa workflow to get a list of IW instead of only the first one
• Loop over IW list with the workflow above
• If only IW the workflow should skip the topsar_merge step

[loreabad6]

Currently if the AOI matches e.g., IW1 from the ref image and IW2 from the match image, we give an error: "Subswaths intersecting the AOI do not match."
Nevertheless, we should handle this case also with TOPSAR merge