Accurate measurement of the group velocity of radio waves in the atmosphere, using radar technique

Measurements of the velocity of propagation of pulses of radio waves through the atmosphere using techniques developed for accurate radio aids to navigation are described. The time of travel of pulses between two ground stations is accurately determined in terms of calibration marks generated by an accurate crystal, account being taken of the measured delays in the receiving equipment. The mean value obtained for the velocity of propagation in the atmosphere at ground level is 299 695 ± 50 km/sec. This value does not differ significantly from that calculated from the best optical values for the velocity of light in free space by allowing for the refractive index of the atmosphere.