Point-Mass Modeling of the Gravity Field with Emphasis on the Oceanic Geoid

摘要

The satellite altimeter adjustments recently performed at AFGL are based on the short-arc algorithm, where the arcs' lengths have been limited to seven minutes or less and the data consists of SEASAT altimeter observations. The smoothed surface approximating the geoid is described by a truncated set of spherical-harmonic (S.H.) potential coefficients and each satellite arc is described by six state vector parameters considered independent from arc to arc. Certain tidal effects are also included in the adjustment. However, each diurnal and semidiurnal constituent considered is attributed only two adjustable parameters: a global amplitude factor and a global phase angle correction. These parameters are shown to be essentially uncontaminated by the geoidal errors or by the systematic orbital errors. Such advantages would not exist if the adjustment were made in terms of S.H. tidal coefficients whose a priori values are used in the present model to describe the approximate behavior of the pertinent diurnal or semidiurnal constituents. The above two parameters represent very special linear combinations of these coefficients. The inclusion of the tidal adjustment in the overall adjustment of satellite altimetry improves the geoidal residuals as well as the 'observed' geoid undulations obtained by superimposing the former on the adjusted smooth geoid. Such 'observed' values can serve to produce a high-degree and order set of S.H. potential coefficients via integral formulas (not via an adjustments), which can then serve in predicting the desired geophysical quantities.