2. Data

Before beginning, it was decided that one year of data, 1998, was to be processed. Although such a time span was unnecessary, at least for the diurnal and semi-diurnal tidal terms, one year of data would

• minimize other effects, such as seasonal or satellite geometrical effects, and the chance that they would alias into the OLT parameters,
• eliminate the need for manual editing because any outlier or otherwise pathological day could simple be omitted with confidence that sufficient data would be retained to achieve a satisfactory solution.

Only permanent tracking sites with easily available data were used to minimize the human resources needed to find, retrieve, and quality control the data.

The large amount of data to be used in this project and the large number of parameters needed for a strict least squares adjustment required that the problem be divided into manageable sized pieces using the Helmert blocking technique. For this reason, the network was broken into a sparse core, and ten regional subnetworks with each region having at least two sites in common with the core subnetwork. The locations of the sites are shown on the associated map. Each subnetwork is designated using a different color/symbol. The core group is designated by yellow triangles.