watsonk1

Bandwidth Selection (and Units!) for Interpolation

Discussion created by watsonk1 on May 21, 2014
Latest reply on May 21, 2014 by watsonk1
Hi Everyone,

I have Arc 10.0 and I'm using the Interpolation with Barriers/Kernel Smoothing to generate a surface to predict oil concentrations in water. The reason I'm using an interpolation w/ barriers is because the coastline is serving as a barrier.

At first I was using the default bandwidth (search radius), until I realized it was somewhat arbitrarily defined as "...the shortest of the width or height of the output extent in the output spatial reference, divided by 30."
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z0000000s000000.htm
Now I've been trying to decide if I should define the bandwidth myself.

One issue I'm having is that I don't know the UNITS for the bandwidth! My dataframe is set to km, but there's no way the bandwidth units are in km, because the number is too small (the average distance between my points is ~10 km, but the default bandwidth is on the order of 0.1).

Qualitatively, the interpolation with the default bandwidth looks good. Not too "spiky" or too "smooth". But I want to publish this eventually and so I'm hoping to have a better understanding of this, and to choose a more appropriate bandwidth if necessary.

In Arc 10.2 they've improved it (http://resources.arcgis.com/en/help/main/10.2/index.html#//009z00000011000000), and I thought about downloading a free trial of that version, but then I'd need to delete the version I have and that might cause some issues that I don't have time to troubleshoot.

So, does anyone know, (1) What the bandwidth units are, and (2), How to go about choosing a bandwidth?

Thanks in advance for any insight you can provide!

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