What is tie-point grids data? and Where did they come from?

I am processing the Sentinel-2 data.
I want to estimate the PM10 concentration with satellite images.
Then, I found AOD (aerosol optical depth), water vapor and etc. data in “tie-point grids” data in the imagery.
Where did they come from?



This is probably a question better directed towards ESA who produce the Sentinel-2 data. You can probably ask this question over in their forum: https://forum.dataspace.copernicus.eu/

Alternatively, you can consult the documentation surrounding Sentinel-2 data products here.