**
Slant path delay model
**

## Introduction

It is currently widely accepted that errors in modeling the variable
path delay in the neutral atmosphere is the major contributor to the error
budget of space geodesy techniques that operate in the radio frequency range:
very long baseline interferometry (VLBI), global positioning system (GPS),
and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS).
Therefore, any improvements in modeling the path delay in the neutral
atmosphere will improve accuracy of geodetic results.
Recent advances in remote sensing and in computer hardware made it feasible
to produce the numerical weather models of the atmosphere with high temporary
and spatial resolution. We expect that the accuracy and resolution of these
models will improve in the future. The output of these models represents the
4D field of the atmospheric parameters. Therefore, the path delay can be
computed * directly* from this field by numerical integration
*without * using inaccurate regression models.

The motivation of this project is **to derive** a rigorous and computationally
efficient algorithm for computing the slant path delay through the
4D, inhomogeneous, elliptical atmosphere designed for processing space
geodesy observations on a global, dense network; **to validate** this model
using space geodesy observation; and **to develop a procedure** for automatic
update of the slant path delays in order to use it for **routine data analysis**
of radioastronomy and space geodesy observations. The algorithm is intended
to be used in a service of the slant path delay computation for processing
VLBI, GPS, and DORIS observations.

## Software

Software package SPD was developed for computing slant path delays by
solving differential equations of wave propagation that produce the wave
trajectory and integration of path delay along that trajectory.
## Slant path delays

Results of slant path delay computation in
ascii format for 218 VLBI sites for the period of time from January 01,
1980 through March 31, 2010 using the output of
MERRA
numerical weather model.
The same slant path delays in
binary format are available as well.

## Validation

... is in progress

*
Web page was prepared by Leonid Petrov
() *

Last update: 2010.02.12_22:36:10