Direct light propagation measurement The noise in measuring the time will be proportional the duration of the pulse For mm-level measurements, need a pulse of the duration equivalent of a few millimeters Pulse strength also enters you need to be able to detect the return pulse) In general, direct time measurement needs expensive equipment a laser system capable of mm-level ranging to satellites costs - $1M 02/25/02 12.540Lec0602/25/02 12.540 Lec 06 6 Direct light propagation measurement • The noise in measuring the time will be proportional the duration of the pulse • For mm-level measurements, need a pulse of the duration equivalent of a few millimeters. • Pulse strength also enters (you need to be able to detect the return pulse). • In general, direct time measurement needs expensive equipment. • A laser system capable of mm-level ranging to satellites costs ~$1M