Phase measurement of distance Phase difference between outgoing and incoming reflected tells something about distance If distance is less than 1 wavelength then unique answer But if more than 1 wavelength then we need to number of integer cycles(return later to this for GPS) For surveying instruments that make this type of measurement, make phase difference measurements at multiple frequencies. (Often done with modulation on optical carrier signal) 02/2502 12.540Lec06 1802/25/02 12.540 Lec 06 18 Phase measurement of distance • Phase difference between outgoing and incoming reflected tells something about distance • If distance is less than 1 wavelength then unique answer • But if more than 1 wavelength, then we need to number of integer cycles (return later to this for GPS). • For surveying instruments that make this type of measurement, make phase difference measurements at multiple frequencies. (Often done with modulation on optical carrier signal)