Hi @zubro,
I doubt there is a dedicated database about tillage, although it would be nice. Apart from asking farmers about tillage timing, you could use the crop calendar. If you know which crop is growing you could deduce when tillage took place. Of course it would be a rough estimation but then you could have a look to several S1 images during that time period an see if something changes.
About SLC/GRD products:
- use SLC when you want to use the phase information (InSAR, DInSAR, etc.) or for polarimetry analysis.
- If you want to use the backscatter information (normalized to sigma0 by radiometric calibration) then your choice should be the GRD products
About coherence for GRD product,
M