Posted 07 June 2011 - 01:48 PM
In this way a variable width canopy cover buffer could be produced. I considered using euclidean distance, viewshed, and cost path tools but none of these seemed to fit the bill. I admit to being flummoxed on this one! Has anyone done something like this before?
Posted 07 June 2011 - 02:32 PM
Posted 07 June 2011 - 02:38 PM
Posted 07 June 2011 - 02:46 PM
On a big river, or a small one that is very sinuous, 500-foot xsection spacing is usually plenty. On a smaller river, 100-foot stationing might work fine. Admittedly, I use AutoCAD to automatically draw lines perpendicular to my measured stream centerline every x-feet along the stream - there may be a GIS tool out there that does this, but I'm not aware of it. Sorry!
Obviously, once the xsections are drawn some may need to be manually adjusted. Then, just intersect and summarize!
Posted 07 June 2011 - 02:46 PM
Are your input datasets already rasters? I've done a similar exercise using vector data where I simply established 500-foot cross-sections along a stream, then intersected the xsections with riparian polygon data. The lengths of the resulting cut-up lines can be summarized by type, thereby giving you the average width of your polygon data.
This sounds about right, but why wouldn't you just create a single 500' buffer for the streams before intersecting the canopy polygons?
edited to add: Answered my own question. I didn't see that Gretchen specifically needs width of canopy versus just a riparian polygon.
Posted 07 June 2011 - 02:52 PM
Bryan - thanks! I understand your process. I'm not sure if I can create those cross-lines in Arc but I will do some searching to figure out if it is possible. If not, I may be able to find a function in GRASS or some other open source GIS. Thank you for your help!
Posted 07 June 2011 - 03:32 PM
David - intersecting a buffer with the canopy cover polygons gives a great measure of total canopy within the buffer but doesn't get at that slightly more interesting statistic of connectivity of canopy to the stream. So if there is a patch of forest that starts at 300' from the stream, for example, it would not be counted because it does not touch the stream. In fact, both measurements are highly useful and total canopy within a set buffer is definitely one of the metrics that will come out of my analysis. It was the connectivity bit that was alluding me.
Yeah, I was initially thinking you were only after a general riparian polygon. As for connectivity I assumed you would select the non contiguous canopy polygons and exclude them from the intersection.
Posted 01 July 2011 - 08:48 AM
Given: a stream polygon layer that outlines the banks of the streams
Given: a tree raster layer (1=tree, 0=no tree)
I have the tree layer (derived via NAIP 1 meter, 2009, 4 band imagery supervised classification) but I only have stream lines, not polygons. The NHD has polygons that would work except not for every stream in my study area. We are thinking about delineating these by hand but it will take some time.
Analysis: Cost Allocation (via ArcMap 10, spatial analyst, in this case) whereby the tree layer and the stream layer are input. The output looks like this (see rough screenshot), though you can see that it would be better if the stream line represented the banks rather than the stream center line.
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