Subsurface radar mapping
it's one thing to make a map showing bright and dark areas. The difficult point is explaining WHAT is causing the amplitude variations.
On Earth, we can find out by digging a hole and looking. This is called "calibration" or "ground-truthing". On Mars it ain't so easy. eventually, we would need to send one or more landers to make shallow drill samples across a traverse and begin to calibrate the dataset.
You can say useful things about morphology and sometimes make process and even mineralogic interpretaions on an uncalibrated map, but calibration is essential for real understanding.