Hi
Some of my own thoughts on backtransforming the variance go as follows:
the backtransform for the variance in lognormal theory is exp{logarithmic
variance-1} times the square of the mean. In kriging this would adapt to
exp{logarithmic kriging variance-1} times the estimated value squared. Again
you can substitute 10 for exp if you use log10 for all the calculations.
However, this is not useful for producing confidence levels since the lognormal
does not follow the Central Limit Theory and a Normal approximation does not
work in practice.
Better to use lognormal theory such as described on the second page of my
extract. The 'Psi' factors provide multiplicative factors for confidence
levels, i.e. you multiply the Psi factor by the estimated value to get a
confidence.
It really depends why you want to backtransform the variance. For a map,
backtransform the variance, maybe just use exp{kriging variance-1} for a
"relative variance". For confidence levels, use the Psi factors.
Hope this helps
Isobel
http://www.kriging.com
