A new "Geometric" mapping function for the hydrostatic delay at GPS frequencies

The hydrostatic mapping function, In(E), is a dimensionless factor which describes the elevation angle dependence of the hydrostatic path delay and relates the line of sight delay to the zenith delay. We have developed a simple "geometric" mapping function where the only free parameter (besides the elevation angle, E) is the climatological pressure scale height. The value of In(E) is given by the ratio of the straight-line ray path length within the first two scale heights above the surface and the ''effective height" defined by these first two scale heights. We used simulated neutral delays at GPS frequencies derived from high resolution ECMWF (European Centre for Medium-Range Weather Forecasts) atmospheric analysis fields (T213L50, T213L60) at different latitudes to compare the new mapping function with others currently in use (we compare with the Niell and the Davis mapping function, respectively, most frequently encountered in literature). At elevations > 6 degrees the geometric mapping function displays, without involving any meteorological data, comparable or better accuracy and precision than the other mapping functions. (C) 2001 Elsevier Science Ltd. All rights reserved.