On holidays, so I'm not online often. I ran a second render to see things "a little bigger". The render below has the atmosphere turned off to see the full effect. Bathymetry data is about 1:1 on screen. The bathymetry image was run through adjust levels - shadows/highlights - levels - shadows/highlights - levels to get a more aesthetic result. With the atmosphere on the effect is a lot more subtle and looks quite good.
At lower altitudes however the data is inadequate to produce a good looking result so it may be necessary to hack a fake depth for shallow water using a blurred terrain mask and merging that with the low res bathymetry data.. but that's potentially quite difficult.
There's a small glitch along a seam east of NZ (look near shallow water at top left) which I've since fixed. This was due to the distortion of low res data when converting to UTM projection.
I've also created some extra terrains for the bigger islands to the south and east of NZ (no overlap = no masking needed
) Additional subsurface "detail" was removed for this render. Now for some extra surfacing on the terrain....