Based on numerical calculations an eхplicit dependence of the perigee altitude of sighting line Hs on the angle of total (astronomical) refraction r has been obtained. An accuracy in determining Hs has been analyzed for different seasons and regions of the Northern Hemisphere. It is shown that in order to reduce the effect of errors in measuring r as well as to minimize the effect of seasonal and regional peculiarities of the refractive index field on the accuracy of determining Hs it is advisable to carry out spaceborne measurements of the total refraction angle within the 10.5—11.5 km altitude range.