[Sgems-users] About SISIM

[nico r. <nic...@gm...>]

I am having a confusion with my indicator simulation results from GEMS.



I am simulating (SISIM) biomass distribution, generated 100
realization over around 19000 grid locations. I have extrapolated the
lower tail and upper tail to the lowest value (which is 2) and the
highest value (139) in the biomass distribution. All 100 simulated
maps have values ranging from 2 to 139. I generated E type map, which
is the average of the 100 simulations, and the E type map has a lot
narrower range of predictions (predictions range from 10 to 45). The
simulation grids in this case do not coincide with the data locations,
therefore, I can imagine my simulated E type map having lower range in
predictions. However, I assume that if the simulation grids would also
have the true data locations, then kriging being an exact
interpolator, I would presume that my E type map would show
predictions from 2 to 139.



To check this further, I made another set of simulations. But in this
case, the simulation grid also has the true data locations. In the
results, while the simulated maps have ranges from 2 – 139, the e type
map still has lower range in predictions. I checked the simulated
values for the true data locations (which were in the simulation
grid), and the simulated values are different from the true value
here. And in this case, as we could expect, the E type map does not
re-produce the true value for these locations. Kriging being exact
interpolator, I was expecting that in these true data locations, the
all simulated values should be the true biomass data; in this case the
E type map would show the true observed biomass values, and the
variance would be zero.



I must be making some mistake in doing the analyses. Do you have any
thought what could be going wrong.



Thanks for your time

Sanjay