Here we compute the mapping function
using the Mendes,Prates,Pavlis^2,Langley model of 2002
Geophysical Research Letters, Vol 29, No. 10 1414, 2004
Improved Mapping Functions for Atmospheric Refraction
Correction in SLR.
which I also call Paper X
In this paper, they present two models:
FCULa is for data that has location + meteorology
FCULb is for data that has only location and day of year
Here we only compute FCULa
so we do require meteorology.

This mapping function depends only on:
1. Temperature
2. Orthometric height of the ranging station
3. Latitude of the ranging station
4. (of course) Elevation Angle of the line of sight

This code is called from eatctl.f
depending on the value of Ict(23)
Ict(23) is binary coded
Mapping    Zenith
0       EATMDL   EATZDL
1       EATMMP   EATZDL
2       EATMDL   EATZMP
3       EATMMP   EATZMP

INPUTS:
i    = site number as determined in eatctl.f
wetz = zenith delay of the wet component of the atm. (sec)
dryz = zenith delay of the dry component of the atm. (sec)
zen  = zenith angle of line of sight  (radians)

Shgt(i) = height of tracking station above reference ellipsoid (km)
hgtOrth = orthometric height of the station in meters
orthometric height is the height above mean sea level
because we do not know the distance between the ellipsoid and
the geoid, we take the orthometric height to be the height above
the ellipsoid (i.e. hgtOrth=Shgt(i)*1000)
elevRad = elevation angle in radians