The specific activities in the proposed study include:

1. The addition of newly available satellite tracking data and altimeter measurements from current missions for the potential improvement of the long wavelength component (>1000 km) of the global geoid,

   and

2. The development of techniques to include non-altimetry dynamic topography information as constraints (in situ and oceanic general circulation model output) to potentially improve the determination of global marine geoid.

1. Improvement and Accuracy Assessment of Geoid Models The objective of the investigation is to improve the long wavelength component of the global geoid model (>1000 km) using satellite tracking and altimeter data. We propose to conduct the following specific tasks in this area:

   1. Satellite tracking and altimeter data will be used to improve the long wavelength component (>1000 km) of the global geoid model and effort will be focused on the attempted separation of geoid signals from the large-scale dynamic topography. The identified data to be analyzed (in the form of gravity information equations) include the following:
      • Satellite laser tracking data from ERS-1, ERS-2, Stella, Lageos-2, and GFZ-1.

      • Tranet doppler tracking data from Geosat Exact Repeat Mission (ERM) and the classified Geodetic Mission (GM).

      • Satellite-to-satellite GPS tracking data from TOPEX/POSEIDON, GPS-Met, EUVE, Radcal, Wakeshield, Orsted, and the Geosat Follow-on Mission as these data become available.

      • Satellite-to-satellite TDRSS tracking data from low inclination satellites, ERBE and EUVE.

      • Satellite altimeter normal point ('filtered') measurements from ERS-1 (35-day repeat and 168-day repeat interleave mission phases), ERS-2 (35-day repeat), TOPEX/POSEIDON, Geosat GM, and if available, GFO 17-day repeat.

      • If available, the global surface gravity anomaly data from the DMA/ GSFC gravity modeling effort.

   2. Using the improved gravity field information equation derived from satellite tracking data and altimeter data, methodologies will be developed to make use of non-altimetry dynamic topography information for potential future improvement of the global marine geoid model. The specific approach includes the use of numerical OGCM model output of mean dynamic topography and in situ data as a constraint in the solution process to allow improved separation of geoid and dynamic topography. The representations of the dynamical topography model, as surface spherical harmonics, or as discrete gridded surface heights, will be assessed for computational efficiency and effective constraints to allow improved geoid-topography separations. The proposed OGCM dynamic topography model output and hydrographic data to be used include the following:
      • Predicted dynamic topography maps from the LANL OGCM during TOPEX/POSEIDON data time span.

      • Dynamic topography maps from TOPEX/POSEIDON data assimilation of the LANL OGCM, e.g., from JPL.

      • Recent hydrographic dynamic topography maps from S. Levitus.

      • Dynamic topography maps during the TOPEX/POSEIDON data time span from the free-surface OGCM developed by B. Semtner.

   3. Accuracy assessment of the available geoid models, including the OSU-91A, the JGM-3 model, the GRIM4-CB model, the soon-to-be-available DMA/GSFC model, the TEG-3 model, and the experimental models obtained during the proposed investigation, will be conducted. The emphasis will be focused on the geoid accuracy assessment over oceans. The accuracy assessment will provide error estimates of the geoid model in terms of frequency and wavenumber spectra, and error prediction based on solution covariance matrices.

2. Accuracy Assessment of Mean Sea Surface Models. An effort will be conducted to improve the University of Texas Mean Sea Surface Model (CSRMSS95) by including additional altimeter measurements. Error assessment of available global mean sea surface models and the experimental models from this investigation will be performed to provide an assessment whether accurate determination of oceanic variability using altimeter measurements collected by satellite missions with non-repeat orbits is feasible. Error assessment of the mean sea surface models will be conducted in terms of frequency and wavenumber spectra, and geographical errors based on covariance/variance predictions. The identified additional satellite altimeter measurements to be used for the mean sea surface model improvement include:
   • ERS-1 35-day, 3-day, 168-day repeat and interleave orbit missions.

   • ERS-2 35-day repeat orbit mission.

   • Geosat Geodetic Mission.

   • TOPEX/POSEIDON mission.

Proposed Deliverables

The anticipated end product will be:

• An improved long wavelength global geoid model.

• The statistical error categorization of the geoid in terms of covariance prediction.

• An assessment of the errors in the mean sea surface model and the influence of these errors on measurements of oceanic variabilities recovered from the use of altimeter measurements from non-repeat orbits.

CSR/TSGC Team Web