Atmospheric Refractions and Radio Telescope Pointing Corrections

In this article we discuss the effects of the atmospheric refraction,particularly,the method of accurate corrections to the pointing error of radio telescopes.The position of the telescope beam is somewhat different from the beam position as indicated by the encoders,which is due to the structural deformations caused by the wind,gravity,temperature,and the atmospheric distortion.Accurate refractive corrections which depend on astronomical pointing measurements are required by observations using large aperture radio telescopes,especially at higher frequency bands.This article presents the advanced model for atmospheric refraction corrections and shows the improvements compared to traditional methods,particularly at low elevations.In addition,the real-time refraction corrections,in which the higher-order refraction corrections of telescope pointing errors are involved,for example,the effect of the uneven temperature distribution over a wide scale range,or the differential refraction across a large aperture telescopes,are also analyzed in this article.