Derivation of the Most Reliable Geoid in the Area of Japan and Some Comments on the Variablility of Sea Surface Topography

Abstract

A geoid in and around Japan has been newly determined within the rms error of 20 cm using both satellite altimeter data and surface gravity data. The area of the estimation is between 20° and 50° N and 120° and 150° E, where geoid heights and their formal errors at the centers of 5’x5’ blocks are evaluated by use of the Least Squares Collocation. The data sets employed are land and surface ship gravity data, GEOS-3, SEASAT and GEOSAT altimeter data. These are almost all the data available in the area. In addition to these data, we have employed OSU86F geopotential model as a reference field and 5’ version of TUG87 height data to remove terrain effects. To clarify the effects of the data selection, the estimation has been carried out for each of the following data combinations: (1) gravity data only, (2) altimeter data only, (3) all the gravity data supplemented partially by altimeter data where the gravity data are not available, and (4) all the altimeter data supplemented partially by gravity data where the altimeter data are not available. From the comparison between each result and its formal error estimate, we can conclude that the third case is the most reliable. The shape of sea surface topography, on the other hand, should be detected from comparison between the first and the second cases. From the present results, however, the detection of sea surface topography has proved to be still difficult because of poor determination of the gravimetric geoid.