Wet zenith path delay of radio waves propagation through the neutral atmosphere
Zenith wet path delay in the neutral atmosphere has been computed at the global
grid 0.25° x 0.3125° grid using numerical weather model GEOS-57 developed
at the Global Modeling and Assimilation Office of the NASA GSFC.
Wet zenith delay is determined the following way. The refractivity index of wet
air at temperature T:
n = k1 * Pd/T + k2 * Pw/T + k3 * Pw/T2
where Pd is the partial pressure of dry air and where Pw
is the partial pressure of water vapor. Using equation of state, the formula can be
rewritten as n = nd + nw, where
nd = k1 * R/Md ρ, and
nw = (k2 - k1 Mw/Md) * Pw/T +
k3 * Pw/T2.
Here ρ is air density, R — universal
gas constants, Mw and Md are molar mass of water vapor and dry air
Then zenith path delay can be determined as
τw = ∫∞
(nw(h) - 1) dh, where integration is over the height
h along the plumb line from the surface to the top of the atmosphere.
Time series of zenith path delay on a global grid for 2012 with 3 hourly
The output of the numerical weather model GEOS-57 has been processed to
determine Pw(h) and T(h) at nodes of
0.25° x 0.3125° x 72 x 3h 4D grid. The zenith path delay
was determined by numerical integration of nw(h). Results of
integration in HEB-format are available for downloading
here (2920 files, 3.3Mb per epoch,
The movie of changes in zenith path delay at a global grid over 2012
The time series of zenith wet path delay from GEOS-57 can be visualized
as a movie
(4:52 duration, mpg format, 34MB).
Back Astrogeo Center.
This page was prepared by Leonid Petrov
Last update: 2013.06.26_22:08:05