SATELLITE NAVIGATION BY TERRESTRIAL OCCULTATIONS OF STARS 2: CONSIDERATIONS RELATING TO REFRACTION AND EXTINCTION

The refraction and extinction of starlight in the earth's atmosphere, including extinction due to the clouds, as applied to satellite navigation ARE DISCUSSED. It is concluded that the unpredictable variation in the amount and height of clouds make the observations of occulations at the earth's true edge unsuitable. A method of virtual occultation is described in which a change in direction, intensity, etc., of starlight due to passage through the atmosphere yields information from which the impact parameter of the observed ray can be determined and the satellite orbital elements calculated. Light extinction is preferred over refraction. A wave length band covering all or part of the region between 0.3 and 0.55 microns s recommended for extinction observations. Calculations of extinction in the atmosphere are presented and further improvements are described. An error of approximately 1/2 km in the satellite position measurement is anticipated due to unpredictable variations in atmospheric density.