Surface color gradient (interp) over a "Geo background"

Ia ora na,

I'd like to represent GHI data over time in a day and across a geolocalised array both as a transparent color-gradient surface and over a geo (topographic) map background. I already tried functions like geodensityplot, looked at geoscatter, scatter3.

For now I get either this, with surf [1] and geoshow [2] (notice there are 7 x 5 nodes for each image) :

... and I would like to get something like :

(sorry, it's a crappy montage but I'm sure you get the point)