s.surf.tps problem

[g681110063 at ntou66.ntou.edu.tw]

Hello,
I am creating a sea-floor elevation model with s.surf.tps, the source
data is from digitized bathymetry points labeled with there respective
depths.  The resulting raster layer has "above zero" elevations that
appear to be related to sharp drops in depth.  The small amount of
documenation I have suggests increasing the tension, however, an increase
great enough to level the "overshoots" results in my depth locations
appearing as a "sink hole" on the ocean floor.  Any suggestions would
be greatly appreciated:)  Are there any net sources for s.surf.tps
documentation?

Thanks in advance!

Eric Grinaker
National Taiwan Ocean University
Keelung, Taiwan, ROC
g681110063 at ntou66.ntou.edu.tw