Correction of atmospheric refraction errors in radio height finding

At mospheric refract ion errors in heigh t finding radars ar c studied by means of detailed r efract ion calculations for a wid e range of meteorological conditions. For targets up to 70,000 feet a bove ground and 150 miles ground distance from t he radar site, t he mean height e rror was found to be as mu ch as 5,000 feet with a standa rd deviation of 1,200 feet. A correction for t he surface value of t he refractive index at t he radar s ite would eliminate t he mean height error and reduce the max imum standard dev iation to less t ha n 900 feet. An additional co rrec t ion for t he init ial grad ient of the refract ive index and t he value of t he r efract ive index at one ki lometer above t he surface would reduce t he maximum standard deviat ion lo less t ha n 400 feet . Methods of correcting he igh t errors based on available meteo rolog ical data a rc prese nted an d shown to be operationally practical.