Correct. The easiest way to calibrate a GPR is to stick a metal plate in the ground and cover it with a few feet of earth dug up on location. Can’t do that with some awkward rovers and an experimental helicopter.
NASA can do some fancy signal processing to get some useful data but until its properly calibrated, any interpretation of that data especially visual should be taken with a Phobos sized grain of salt.
NASA can do some fancy signal processing to get some useful data but until its properly calibrated, any interpretation of that data especially visual should be taken with a Phobos sized grain of salt.