Estimability of Geodetic Parameters from Space VLBI Observables

Loading...
Thumbnail Image

Date

1990-07

Journal Title

Journal ISSN

Volume Title

Publisher

Ohio State University. Division of Geodetic Science

Research Projects

Organizational Units

Journal Issue

Abstract

In the 1990's dedicated radio telescopes will be launched into Earth orbit and will be integrated in the ground-based VLBI networks. A straightforward extension from present ground-based VLBI to space is called space VLBI, which uses radio-antennas in space. In the simplest version of the space VLBI technique, one station in orbit observes in conjunction with a second station on the ground. However, in practice we have a number of networks of ground antennas observing the common celestial radio sources simultaneously with a conventional VLBI technique. Moreover, joint observations of two or more space VLBI satellites will supposedly be performed in the future. Therefore, in our research work a combined use of simultaneous space and ground-based VLBI observations are considered from the geodetic and geodynamic point of view. This investigation studies the feasibility of space VLBI observables for geodesy and geodynamics. A brief review of space VLBI systems from the point of view of potential geodetic application is given. A selected notational convention is used to jointly treat the VLBI observables of different type of baselines within a combined ground/space VLBI network. The basic equations of the space VLBI observables appropriate for covariance analysis are derived and included. The corresponding equations for the ground-to-ground baseline VLBI observables are also given for a comparison. The simplified expression of the mathematical models for both space VLBI observables (time delay and delay rate) include the ground station coordinates, the satellite orbital elements, the earth rotation parameters, the radio source coordinates, and clock parameters. The observation equations with these parameters have been examined in order to determine which of them are separable or nonseparable. Singularity problems arising from coordinate system definition and critical configuration are studied. Linear dependencies between partials are analytically derived. The mathematical models for ground-space baseline VLBI observables have been tested with simulation data in the frame of some numerical experiments. Singularity due to datum defect is confirmed. Recommendations are given for future research work.

Description

Prepared for the National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, Maryland

Keywords

Citation