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

The hydrostatic mapping function, In(E), is a dimensionless factor which de scribes the elevation angle dependence of the hydrostatic path delay and re lates the line of sight delay to the zenith delay. We have developed a simp le "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" d efined by these first two scale heights. We used simulated neutral delays a t GPS frequencies derived from high resolution ECMWF (European Centre for M edium-Range Weather Forecasts) atmospheric analysis fields (T213L50, T213L6 0) at different latitudes to compare the new mapping function with others c urrently 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 precis ion than the other mapping functions. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.