Choosing the right method

Discussion created by ashleydia on May 25, 2011
Latest reply on May 25, 2011 by ashleydia
I am attempting to create an interpolated surface of noise with the Geostatistical Analyst extension. I am not an expert, so please excuse my ignorance here.

I have 27 points of decibel measurements over approximately 475 square miles. One of the points towards the edge of the study area would be considered an outlier (it is about 25 db more than the second highest measurement).

After reviewing the Classification trees of the interpolation methods offered in Geostatistical Analyst, I think I should use either IDW or GPI. I am reluctant, however, to rely on the GPI, because of my outlier on the edge of my study area.

I am concerned about my sample size of 27. I have read that having less than 30 points can hurt reults in these types of spatial operations, which is why I choose methods that don't rely on spatial autocrrelation. Is there anything else I should be aware of?

I am also concerned about any behind the scenes math that the models may use, because decibels have a logarithmic relationship, one cannot simply arithmetically add, subtract, or average decibel levels. For example if you have two 60 dB noise sources occurring simultaneously they combine to equal 63 dB.

Help and advice is most appreciated!