I am having some trouble with basic understanding of geostatistical analyses. I am interested in figuring out at what bin size (or EDSU unit) my fish density estimates from hydroacoustics data is autcorrelated and at what distance it is not correlated. Eventually, I will also want to compare variance estimates from geostastical methods to arithmatic methods, as well as krig my density estimates over the entire reservoir. I know I need to calculate an experimental variogram and then fit a model to that variogram, and based on that plot I can tell at what distance my data is autocorrelated vs not. However, when I run my data through a script I put together to do just this, the variogram plots I get back are nothing like I've seen in any manuscript or help page online.
I am working in very small reservoirs, and our survey design is zig-zag transects. The data I feed into the script are density estimates calculated in 50-m vertical bins, summed over the water column depth. Perhaps my variogram looks odd because the bin size I use to feed my analyses is too small? Should I try out different bin sizes? Why is my nugget effect so large (4000)?
Running a simple correlation (density vs northing, and density vs easting) to determine if there is anisotropy, it does not appear that there is any. Therefore, I calculated an experimental omni-directional variogram.
Are there any steps I am missing? Does my variogram look ok? Should I be feeding in different data?
If you could provide an email address so that I can send my script, along with csv data file, and shape file of the lake, that would be great.
Thank you.