Using the elevation map of the San Francisco Bay area illustrated in Figure , a second test was conducted to assess the applicability of the method in 3D. The maximum surface topographic relief is approximately 800 m; however, the elevation gradients and topographic wavelengths are significantly smaller and longer than the 2D test illustrated in Figure . The flat subsurface datum is set a depth of 8000 m.
Figure 4 Elevation map of the San Francisco Bay area used in 3D testing.
Figure presents the slices through the 3D potential function results. The top panel shows a depth slice at approximately zero elevation, whereas the lower two panels show slices along Easting (bottom left) and Southing (bottom right) directions.
These profiles illustrate a PF that is smoother than the previous example.
Figure shows the coordinate system generated along the same two slices shown in the panels b) and c) of
Figure . The generated coordinate system much smoother than in the previous example, as expected from the smoothness of the PF. Figure presents a perspective view of the ray-traced coordinate system results.
The coordinate system rays are fairly straight, except in the region beneath topographic highs. Another way to visualize the ray coordinate system is to examine how the topography 'heals itself' at various steps. Figure illustrates this for the (top left), (top right), (bottom left) and (bottom right) surfaces, where N is the total number of extrapolation steps.
The sidebars show the elevation difference between the lowest and highest points of each equipotential surface. The greyscale intensity has been clipped according to the maximum elevation difference at .