Improvement on Atmospheric Hydrostatic Delay Correction at Low Elevation Angles

Observation made at low evelation angles is the trend of development of GPS (Global Positioning System) meteorology, wherein the development of highly accurate atmospheric hydrostatic delay corrections at low elevating angles is the main key technique. The comparison among three methods for calculating the atmospheric hydrostatic delay correction of the radio waves from space to the ground-based receiver is made: (1) the atmospheric hydrostatic delay obtained from the path integration of the sounding balloon data under the assumption of atmospheric spherical symmetry, (2) the atmospheric hydrostatic delay acquired from the reanalyzed data of the NCEP (National Centers for Environmental Prediction) under the assumption of atmospheric spherical symmetry and (3) the atmospheric hydrostatic delay got from Niell's atmospheric hydrostatic mapping function. The results of the comparison of them with the atmospheric hydrostatic mapping function obtained from the calculation carried out by taking advantage of the data acquired at 89 sounding balloon stations in China in 2001 show that the accuracy of the method of the path integration of the reanalyzed data of NCEP at low elevating angles (bellow 5°) is about 5 times better than that of the Niell mapping function model.