Monitoring of a golf ball and apparatus for doing so is described using differential time locating. Launch parameters of a golf ball can be characterized independent of any specific positional measurement on the basis of a ball signal that is transmitted from the ball. These parameters include initial spin, initial velocity, and initial trajectory. Ground proximity detection is described as well as a landing position and rollout position detection technique and associated apparatus. Calibration techniques are described for various kinds of range receivers that subsequently receive the ball signal.