Here take S1A-IW-SLC-1SDV as an example.
The grd data cannot be decomposed by polarization and has no phase information.
SNAP processing
1. Track correction
Radar→Apply Orbit File
I/O Parameters: naming, format, address.
two,
Radar→Sentinel-1 TORS→S-1 Slice Assembly
plus sign pointed by arrow twice
select all
Run
three,
Radar→Sentinel-1 TORS→S-1 TORS Split
IW1
Same for IW2
IW3
4. Radiation Calibration
Radar→Radiometric→Calibrate
I/O Parameters: naming, format, address.
Processing Parameters: Select Save as complex output, the first
Same for IW2
IW3
five,
Radar→Sentinel-1 TORS→S-1 TORS Deburst
Same for IW2
IW3
six,
Radar→Sentinel-1 TORS→S-1 TORS Merge
seven,
Right mouse button →Add→Raster→Subset
To be continued...
Reference: Polarization of Sentinel-1 in PolSARpro_哔哩哔哩_bilibili