Geodetic and Geodynamic Contributions from ERS-1 and ERS-2

B. Tapley, C. Shum, J. Ries, and M. Kim

Center for Space Research, The University of Texas at Austin,
Austin, Texas 78712, USA.  Tel: 512-471-5573, Internet:
tapley@csr.utexas.edu

The launch of ERS-1 in 1991 initiated a decade of planned radar
altimeter missions for active sensing of the global ocean 
surface topography.  Altimeter-inferred sea surface topography
is a geocentric measurement.  To achieve the necessary accuracy
of this measurement, a number of inherent requirements are
needed.  These requirements include broad modeling knowledge 
from a number of interdisciplinary areas of Earth science,
including geodesy and geodynamics.  Together with the NASA/CNES 
TOPEX/POSEIDON radar altimeter measurements, significant 
progress have been accomplished using ERS-1 measurements 
to geodynamic and geodesy.  These modeling knowledge include
Earth's shape and mass variations, and the associated accurate
representation of the terrestrial reference frame.  One inherent
requirement is the knowledge to compute orbit of teh ERS
satellites with respect to the center of mass of the Earth to a
few centimeters.  Current radial orbit accuracy from ERS-1 
and ERS-2 is approaching the 5 cm cm rms level, which is a 
consequence of significant improvement in the knowledge of 
Earth's shape and mass distribution and the definition of the
terrestrial reference frame.  These improvement was acheived 
using the radar altimeter and tracking measurements from ERS-1
and other satellites.  High-resolution mean sea surfaces have 
been developed using ERS-1 and other altimeter data 
and have significantly improved our knowledge of gravity 
and the shape of remote ocean basins.  Improved long 
wavelength geoid, specifically using tracking and altimeter 
data from ERS-1, has enabled improvement in the dynamic 
topography model, which is critical to understand the role 
of the ocean in global heat transport.  Finally, ERS-1 and ERS-1 
radar altimeter measurements contributed to the potential 
use of long-term radar altimeter measurements for the 
monitoring of regional and global mean sea level variations.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry