To what extent would the vertical variogram sill be less than the data
variance before a zonal anisotropy can be considered?
I have this data with horizontal variogram sill (along all azimuths) of
0.0042 but a vertical variogram sill of 0.004. The variance of the data is
around 0.0044. I have taken the horizontal sill to be approximating the
variance. I wonder if I should do the same for the vertical sill and
therefore declare a fully geometric anisotropy; or, if I should take the
vertical sill as indeed less than the sill and therefore declare a zonal