The Matérn family of isotropic covariance functions has been central to the theoretical
development and application of statistical models for geospatial data. For global data
defined over the whole sphere representing planet Earth, the natural distance between any
two locations is the great circle distance. In this setting, the Matérn family of covariance
functions has a restriction on the smoothness parameter, making it an unappealing choice to
model smooth data. Finding a suitable analogue for modelling data on the sphere is still an …