HIRAN

abbreviation of High-intensity Short-range Navigation, electronic-pulse type of instrument introduced in 1935 to measure the distance over water between land survey stations obscured from each other by the Earth's curvature. An airplane flying high enough to be visible from both stations crosses over the line between them while sending out a series of pulses. These are automatically relayed back to the plane from each station. The minimum sum of distances represented by the timed returns is chosen, and the nearby sums are corrected to be averaged with it. The result is corrected for the altitude of the plane and the refraction of the atmosphere, and the final value is taken as the distance between the two stations.