Use of global meteorological models for VLBI data analysis
Motivation
Instrumental errors and mismodeling atmospheric path delay are two major
factors which determine the accuracy of VLBI. Path delay in atmosphere depends
on the profile of refractivity index along the ray path. Unfortunately,
refractivity index in a particularly point of the ray trajectory only weakly
correlate with ground temperature pressure and humidity. So, in order to
adequately model the total atmosphere path delay we have to learn
four-dimensional (4D) distribution of pressure, humidity and temperature
in the atmosphere. Availability of numerical weather models provides us
an opportunity to use this information for better modeling atmosphere path
delay.
Current status
There was an attempt to build a hybrid model, called isobaric mapping
function (IMF). The essence of that approach is to use a set of radiosounde
data, compute mapping function (ration of total atmosphere path delay to
the zenith path delay as a function of elevation) using these data, build
a linear regression model between parameters of the mapping function and
some function of meteorological parameters. Then to use this regression model
for computing mapping function for VLBI observations with use meteorological
parameters from the numerical weather models. In particularly, geopotential
hight at 200 mbar level was used for modeling hydrostatic mapping function
and the ratio of humidity integrals at 3.3 and 90 elevation angles for
wet mapping function. Mode detail about the IMF approach can be found
here.
Another approach is to compute parameters of the mapping function directly
from numerical weather models.
Memos and publications
A. Niell, L. Petrov, Using a Numerical Weather Model to Improve Geodesy,
to be published in Proceedings of "The State
of GPS Vertical Positioning Precision: Separation of Earth Processes
by Space Geodesy".
imf_lux_abs.txt (abstract)
|
imf_lux.ps.gz (Full text, 169Kb).
Back to "Development of advanced methods of VLBI
data analysis"
Back to Leonid Petrov's Home Page
This page was prepared by
Leonid Petrov
Last update: 05-SEP-2003 11:45:33