On the evaluation of stationary sea surface topography using geodetic techniques

Abstract

One of the principal problems in separating the non-tidal Newtonian gravitational effects from other forces acting on the ocean surface with a resolution approaching the 10 cm level arises as a consequence ofall measurements of a geodetic nature being taken eitherat orto the ocean surface. The latter could be displaced by as much as ±2 m from the equipotential surface of the Earth’s gravity field corresponding to the mean level of the oceans at the epoch of observation— i.e., the geoid. A secondary problem of no less importance is the likelihood of all datums for geodetic levelling in different parts of the world not coinciding with the geoid as defined above.

It is likely that conditions will be favourable for the resolution of this problem in the next decade as part of the activities of NASA’s Earth and Ocean Physics Applications Program (EOPAP). It is planned to launch a series of spacecraft fitted with altimeters for ranging to the ocean surface as part of this program.

Possible techniques for overcoming the problems mentioned above are outlined within the framework of a solution of the geodetic boundary value problem to ±5 cm in the height anomaly. The latter is referred to a “higher” reference surface obtained by incorporating the gravity field model used in the orbital analysis with that afforded by the conventional equipotential ellipsoidal model (Mather 1974 b). The input data for the solution outlined are ocean surface heights as estimated from satellite altimetry and gravity anomalies on land and continental shelf areas. The solution calls for a quadratures evaluation in the first instance.

The probability of success will be enhanced if care were paid to the elimination of sources of systematic error of long wavelength in both types of data as detailed in (Mather 1973 a; Mather 1974 b) prior to its collection and assembly for quadratures evaluations.