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Ocean Surface Topography from Space
Combined Estimation of Tides and Bathymetry from Multi-Satellite Altimetry


Edward Zaron - (Portland State University)

  Marie-Aude Pradal
(Johns Hopkins University, Earth and Planetary Sciences)


The objective of this work is to improve knowledge of ocean bottom topography over the continental shelves and in sparsely-sampled coastal areas. Present-generation global gridded bathymetry products are based on the combination of gravimetric data, much of which is inferred from satellite altimeters, and in situ bathymetry. Existing methodologies depend on models of the Earth's crust which are inaccurate at continental margins, and the resulting bathymetry is correspondingly less accurate than in the deep ocean where the crust and sediment are more uniform. We seek to improve the accuracy of bottom topography estimates in regions which are not well determined by existing methodology.
Our approach is based on the assimilation of altimetric sea-surface height measurements into a hydrodynamic inverse model in which bottom topography is a control variable to be estimated. The idea is not new, but we have made significant advances in methodology and covariance modeling which will permit its application in the proposed setting. The dynamics and error analysis are considerably simplified by the consideration of harmonically analyzed (tidal) data; although, the inversion for bottom depth is still a strongly nonlinear inverse problem.
The proposed research will benefit several NASA objectives:
  1. new estimates of the tides over coastal areas will be produced for use as tidal corrections to altimeter data, thus facilitating the use of altimetry closer to land; and
  2. improved bottom topography maps will be useful to operational ocean modelers concerned with societally-relevant water level, currents, and bio-physical environmental forecasting.

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