中性大气折射延迟的研究现状及其天文测量方法

经典天体测量和大地测量所作的天文大气折射修正,以及现代空间大地测量所作的电磁波中性大气折射延迟改正,都没有达到期望的高精度要求,原因在于不能直接测定天文大气折射和折射延迟模型的参数,只能采用各地相同和各向同性的理论模型作改正.为了提高修正精度,人们用测量数据反演各观测站不同方位的经验改正模型.本文根据有关学科发展对空间大地测量的精度要求,阐述了折射延迟量与观测站周围的地形有关的事实,指出了建立和采用随观测站、方向而异的改正模型的必要性;在分析了长期以来直接测定天文大气折射或折射率的几个主要障碍和已具备的条件后,根据光学波段的天文大气折射与射电波段的大气折射延迟之内在联系,提出了在各测站采用天文大气折射测定值,建立各自随方位而异的大气折射实测模型和折射延迟实测模型的方法;文中还给出了测定瞬时天文大气折射、建立两种实测模型的总体方案.这一方法的实施,将有可能把天顶方向的延迟改正精度提高到1mm以内、高度角5°处的精度提高到厘米量级,并且把截止高度角压缩到5°以内.

The Investigative Status of the Neutral Atmospheric Refraction Delay and Its Astronomical Measure Method

Neither the astronomical atmosphric refraction correction of the classical astrometry and geodesic surveying nor the neutral atmosphric refraction delay of electromagnetic waves of modern space geodesy can meet the high accuracy requirements. The prime reason is that the astronomical atmosphric refraction and the parameter of refraction delay model can not be directly determined, and it is obliged to use the same isotropic theoretical model in all parts for correction. To improve the corrected accuracy, the experimental correcting model in different azimuth was built by the ex-post process of the determined data. According to the accuracy requirements of space geodesic surveying in the development of concerned subjects, the fact that the refraction delay quantity is related to topography around the observing station is clarified, and the necessity changing the correcting model with the observing stations and azimuths is pointed out. After analyzing several major obstacles to measuring the astronomical atmospheric refraction value directly and the existing conditions for removing these obstacles, based on the internal relations between the astronomical atmosphric refraction in optical band and the refraction delay in radio band, a new method is proposed： the determined data of the astronomical atmospheric refraction values at different station are utilized to build the observational astronomical atmospheric refraction model and refraction delay model, which change with the azimuths. In this paper, the general scheme for measuring the instantaneous astronomical atmospheric refraction and building two kinds of observational model is given. By means of this new method, the improved correction accuracy of the zenith delay will be within 1 mm, that of the refraction delay at elevation angle 5°to centimeter＇s magnitude, and the cut-off angle reduced to degree 5° or less.