Constructing an Observational Model of the Neutral Atmospheric Refraction Delay from Measured Values of the Astronomical Refraction

Abstract

Discussing the requirements for an accurate correction of the neutral atmospheric refraction delay for the Global Positioning System, our paper points out that the existing theoretical correction models and the old postprocessing methods cannot attain the anticipated accuracy because the atmospheric refraction index has not been directly determined precisely. It is necessary to adopt atmospheric refraction delay models to improve the correction accuracy. The models are dependent on the observing station and the observation azimuth. By the new method we propose in this paper, the observational data of astronomical refractions at different azimuths and different zenith distances are grouped according to azimuth and used to calculate the refractivity and mapping functions. As an example of the newmethod, we introduce the configuration of the Lower Latitude Meridian Circle and the measurement method of instantaneous astronomical refractions, and present the observational astronomical refraction model toward the east, south, west, and north of the Yunnan Observatory. We estimate that, without the use of any atmospheric distribution models, the correction accuracy of the zenith delay will be within 1 mm, the correction accuracy of the refraction delay at the lower elevation will be improved to a centimeter magnitude, and the cutoff elevation angle will be reduced to 5 degrees or less.