topic Re: Calculating beta-diversity with raster data? in ArcGIS Spatial Analyst Questions

Calculating beta-diversity with raster data?

JamesSnider — Thu, 08 Sep 2011 16:16:03 GMT

Hi folks, I'm trying to work out a method to calculate the "beta"-diversity given a Landsat vegetation classification -- essentially to determine how patterns of vegetation change across a landscape.

Unlike "richness" which could be easily calculated using focal stats ("variety"), I'm trying to determine how the composition of the classification changes in space. More on beta-diversity here: http://en.wikipedia.org/wiki/Beta_diversity (It's essentially a measure of similarity)

Theoretically this could be done using features and Python lists (searchcursor) -- eg. create a new list for each quadrant of the classifications values, for intance:

quadrant 1 = [1,2,3,4,5]
quadrant 2 = [3,6,8,9]

and then based on the location of the quadrants (lat-long), I could create a pseudo-moving window to compare the contents of each list for adjacent or nearby quadrants.

Problem is this is >1GB raster that I'm starting with (30m resolution), so conversion to shapefile and subsequent processing is going to be super-slow.

Any ideas as how to perform something akin to what I have described above using the spatial analyst tools? Unfortunately, I don't see a simple focal stats approach here... but perhaps I am missing something.

The other approach I've considered is creating raster dataset for each classification value and then using a local analysis, but unfortunately I run across the same limitation, which is actually implementing the beta-diversity algorithm/calculation...

Any thoughts would be greatly appreciated! For comparison the closest post on here I can find is:
http://forums.arcgis.com/threads/20900-How-do-I-make-a-calculation-on-a-raster-file-within-a-specific-neighbourhood?highlight=raster+diversity

Re: Calculating beta-diversity with raster data?

JamesSnider — Thu, 08 Sep 2011 16:52:27 GMT

At its simplest, I'd like to create a list of values within quadrants (neighborhood/window) and then compare the contents of those lists.

The first step would be to create a list of values -- is that possible using spatial analyst?

Re: Calculating beta-diversity with raster data?

JamesSnider — Thu, 08 Sep 2011 17:53:48 GMT

One additional approach, which might be more closely aligned with the available tools in Spatial Analyst is to reclassify the landcover classification in such a way that a focal sum could create unique outputs based on the values within the neighborhood window

e.g. quadrant1 (3 x 3 grid) = 100,000 + 10,000 + 1,000 + 100 + 10 + 1 = 111,111
quadrant2 = 10,000 + 10,000 + 1,000 + 100 + 100 + 10 = 21,210

such an approach would give both what amounts to a list of values and the relative abundance of each class.

From there, you could simply calculate a second focal stats using 'variety"...

Re: Calculating beta-diversity with raster data?

JamesSnider — Thu, 08 Sep 2011 20:41:22 GMT

I'm realizing my 11 classes would require 64-bit data to perform the analysis described above,whereas the reclassify tool is obviously limited to 32-bit based maximum value(2147483648). Any suggestions?

Ideally the reclass would be as follows:
(input:output)
1:1
2:10
3:100
4:1000
5:10000
6:10000
.
.
.
11: 10000000000

I've considered using 32-bit float and using decimal places, but again reclassify outputs must be integers!

Any advice?

Thanks,
James

Re: Calculating beta-diversity with raster data?

JamesSnider — Thu, 08 Sep 2011 20:52:44 GMT

A nested "Con" statement might do the trick... it can handle floats, right?