Laser measurements of long distances

The extension of radio frequency techniques to the optical region of the spectrum has made possible many types of measurements which were not feasible before. One area in which important scientific contributions can be expected during the next few years is the use of lasers to measure long distances with high accuracy. Three types of distance measurements which have been discussed in the literature and which are now being investigated actively are: 1) interferometric measurements over distances of up to hundreds of meters through evacuated or sealed-off tubes, 2) measurements with modulated laser beams over distances of perhaps one to fifty kilometers with corrections made for the atmospheric index of refraction along the path, and 3) range measurements to artificial satellites and to the moon using laser radar. Some of the possible geophysical and geodetic applications of such measurements will also be discussed.