Well I worked for a mining company in their geophysical services department back in the 1990s. Radar was one of the data sets that the geophysicists used to look for underground rock formations. I don't remember how far down we were able to analyze back then.

It’s not GPR. That graphic is inaccurate. They’re using InSAR from multiple angles and using a new, proprietary AI software they developed to create a model from the interference patterns in the near-surface level readings. Still a lot to verify before it “proves” anything, but it at least gives enough evidence to warrant further investigation as they’re the only ones with access to the software.