Falcon-9 relies on GPS and a couple of altimeters. (Filtered, as others have already said, with the help of data from the inertial sensors.)
Compared to Falcon-9, Starship/Superheavy additionally has a command link from the ground. Whether it is used to coordinate the movement during the catch is not publicly known, but it is easy to imagine how this could be useful.
Compared to Falcon-9, Starship/Superheavy additionally has a command link from the ground. Whether it is used to coordinate the movement during the catch is not publicly known, but it is easy to imagine how this could be useful.