The Urgency for the Study of the Abnormal Refraction

The effects from the atmosphere of our earth on the astrometry are classified and some processing methods in the observations of traditional meridian circles are introduced. In comparison, the corresponding processing methods of the LLMC are also introduced. Since the LLMC can absolutely determine the normal refraction and the slope of the atmospheric isopyknic, it is pointed out that the short periodic and irregular refractions will be the main obstacle to raise the observatinal accuracy and the determination of the abnormal refraction in real time is urgent to clear away the obstacle of the refraction.