Random Tropospheric Angle Errors in Microwave Observations of the Early Bird Satellite

1.1 Objective of this Paper The performance of earth-based radar and optical systems is ultimately limited by temporal and spatial random variations in the refractive index of the tropospheric propagation medium. It is the objective of this paper to present a method for predicting random tropospheric angle errors in such systems, and to compare a prediction with microwave observations made on the Early Bird satellite. 1439 1440 T H E B E L L SYSTEM TECHNICAL JOURNAL, NOVEMBER 1966 1.2 Problem Approach The scintillation or twinkling of the stars which is experienced in observations through the earth's troposphere is a familiar effect of the random variations in the refractive index of this propagation medium. Astronomers have known for a long time that the troposphere actually causes variations in at least four characteristics of the received star light, namely: (i) the intensity, (it) the spectral distribution of the intensity, (in) the shape of the telescopic diffraction image, and (iv) the apparent angular position of the star. Scientific studies1 -2 of these effects seem to concentrate mainly on the intensity scintillations. The random variations in the other characteristics, especially in the apparent angular positions of stars, are treated in much less detail. However, in those radar and optical systems which are used to measure the position (and its time derivatives) of both distant and near objects (such as aerospace vehicles) the random tropospheric angle variations assume great importance.