Therefore, a new method of estimating tide corrections is being developed. First, the method spatially interpolates each tidal constituent's amplitude and phase throughout the region and makes a tidal prediction. This predicted tide is then added to the residual component and the offset, which are computed by spatially interpolating the values at the shore. However, at any point located some distance away from any of the gauges, the value of each component is usually not known. That is, by summing the weighted value of the component at each of the nearby water level gauges.
N r is the number of stations where the residual water level is measured.
Therefore, a set of weighting functions is needed, one weighting function for each water level station. And because there is often a different group of water level stations supplying data for each component of C, a different set of weighting functions is needed for each component. As an example, a plot of the instantaneous astronomic tide in Galveston Bay, as determined by summing the spatially-interpolated harmonic constants, is shown in the figure to the right. The grid consists of squares, one-third of a nautical mile on a side. In each estuary, the water levels were measured by a small craft on several traverses of a fixed course and then referenced to the ellipsoid.