Priors

skretrieval.retrieval.prior.VerticalTikhonov(order)	A prior that is constructed as a Tikhonov constraint.
skretrieval.retrieval.prior.ManualPrior(...)	A prior that is manually specified, both the prior state and it's covariance
skretrieval.retrieval.prior.ConstantDiagonalPrior([value])	A prior that is constant along the diagonal.