Gravity Recovery Using COSMIC GPS Data: Application of Orbital Perturbation Theory
Loading...
Date
1998-10
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University. Division of Geodetic Science
Abstract
COSMIC is a joint Taiwan-US mission to study atmosphere using GPS occultation. Its GPS data
for precise orbit determination can be used for gravity recovery. In this report a kinematic
approach was employed which assumes the positional data can be derived from the GPS data of
COSMIC in the operational phase. Using the geometric relationship between the positional
variations of orbit and the variations in the six Keplerian elements, improved formulae for the
radial, along-track and cross-track perturbations were derived. Based on a comparison with true
perturbations from numerical integrations, these formulae are more accurate than the commonly
used order-zero formulae. The improved formulae were used to simulate gravity recovery using
the COSMIC data. In one simulation with the OSU91A model to degree 50 as the a priori
geopotential model, it is demonstrated that the EGM96 model can be improved up to degree 26
using one year of COSMIC data.
A significant effort was devoted to the recovery of temporal gravity variation using
COSMIC data. Sea level anomaly (SLA) was first generated using the Cycle 196
TOPEX/POSEIDON altimeter data. The steric anomaly due to thermal expansion was created
using temperature data at 14 oceanic layers. The steric anomaly-corrected SLA was used to
generate harmonic coefficients of temporal gravity variation. With a 3-cm noise at a one-minute
sampling interval in the COSMIC data, the gravity variation cannot be perfectly reproduced, but
the recovered field clearly shows the gravity signature due to mass movement in an El NiƱo.
With a 0.1-cm noise, the temporal gravity variation up to harmonic degree 10 is almost exactly
recovered and this prompts the need of a better processing technique and a sophisticated GPS
receiver technology.
Description
The idea described in this report was initiated during the author's visit to the Ohio State University in the
Summer of 1998, hosted by Prof. C.K. Shum.
This research was partly supported by the National Science Council of ROC.
This research was partly supported by the National Science Council of ROC.