On the incorporation of sea surface topography in establishing vertical control

Abstract

One of the major sources of distortion in vertical control networks is caused by neglecting sea surface topography (SST) at tide gauge stations. Often, the orthometric height is fixed to zero at these stations without applying proper corrections for the deviation of the mean sea surface from the equipotential surface represented by the geoid. In view of the significant improvements in SST determination made in the past decade (particularly the low-to-medium frequencies) and the expected improvement in global gravity field models in the near future, it is appropriate to consider practical methods for the incorporation of SST into establishing vertical control. The purpose of this paper is to develop a consistent procedure for incorporating the mean SST values into the combined height network adjustment of terrestrial GPS-on-benchmark data and GPS-on-tide gauge data typically located in coastal areas, harbours, estuaries and/or river mouths. Two main issues that arise for the proper incorporation of SST information into the optimal heterogeneous height network adjustment include (i) the modelling of systematic errors and datum discrepancies among the height data types (ellipsoidal, orthometric, geoid and SST) using a corrector surface and (ii) the separation of random errors for estimating variance components for each height type. The limiting factor in all of these studies is data availability or rather lack of quality data and obtaining reliable initial covariance matrices for the height data in a particular region. However, in lieu of the increased need for cm-level accurate vertical control it is expected that this situation will be significantly improved in the near future.