Precise Tracking Trhough the Uncertain Atmosphere

Bias errors caused by tropospheric refraction may now be corrected to a level * below the threshold of the best radars • In most cases 9 only surface weather data is needed for this. The errors which remain will fluctuate at frequencies from one cps down to one cycle per day, or less, and will lead to serious errors in both radar and interferometer systems. Long baselines reduce the error f but the presence of long-period components in both space and time causes the error to drop very slowly as the baseline is extended. Effects of these components on position and velocity •data are shown. Although ionospheric errors can be held to the required level by using frequencies above 3000 me, it is concluded that precise tracking systems must use trilateration over very long baselines to achieve the accuracies now desired