GRAVITY-FIELD IMPROVEMENT IN THE MEDITERRANEAN-SEA BY ESTIMATING THE BOTTOM TOPOGRAPHY USING COLLOCATION

The contribution of bathymetry to the prediction of quantities related to the gravity field (e.g., gravity anomalies, geoid heights) is disc ussed in an extended test area of the central Mediterranean Sea. Sea g ravity anomalies and a priori statistical characteristics of depths ar e used in a least-squares collocation procedure in order to produce ne w depths, giving a better smoothing of the gravity field when using a remove-restore procedure. The effect of the bottom topography on gravi ty-field modeling is studied using both the original and the new depth s through a residual terrain modeling reduction. The numerical tests s how a considerable smoothing of the sea gravity anomalies and the avai lable altimeter heights when the new depth information is taken into a ccount according to the covariance analysis performed. Moreover, geoid heights are computed by combining the sea gravity anomalies either wi th the original depths or with the new ones, using as a reference surf ace the OSU91A geopotential model. Comparing the computed geoid height s with adjusted altimeter sea-surface heights (SSHs), better results a re obtained when subtracting the attraction of the new depth informati on. Similar results are obtained when predicting gravity anomalies fro m altimeter SSHs where the terrain effect on altimetry is based on the new bottom topography.