This article may be helpful.
Citation: Duhl, T.R., A.B. Guenther, and D. Helmig, 2012: Estimating urban vegetation cover fraction using Google Earth® images. Journal of Land Use Science, 7, 311-329, DOI: 10.1080/1747423X.2011.587207. Monica Madronich, PhD University of Colorado/National Center for Atmospheric Research [email protected] On Jul 1, 2013, at 5:17 PM, John Mickelson <[email protected]> wrote: > Since you're mostly dealing with digital versions of air phot > Hi Jeff, > > Since you're mostly dealing with digital versions of air photos, (as opposed > to histogram matched and calibrated satellite data) you're immediately going > to be either hand extracting or "photo-interpreting" the extent of the canopy > layer within each of the images or (potentially) using an automated > (machine segmentation program) like eCognition, which, depending on a range > of factors contained within each image set (lighting, texture, time of year, > resolution, parallax, etc....).... Either way, you're best off by having the > same person(s) perform the analysis so that areas considered to be "FOREST" > can be more uniformly assessed and mapped. (at some point you have to decide > "how big does a tree or forested patch have to be, to be considered > "FOREST".... with a virtually uniform gradient, spatially as well as > temporally, from BARE SOIL to MATURE FOREST, that break line can be tricky to > hit. > > You'll have to be aware of a number of error factors within the work; how > well each year\image epoch was "georeferenced", (or superimposed within a > real-world feature space) both to real world features as well as each > other... whether elevation factors were included in the correction process > (ala orthocorrection processes to remove terrain displacement), etc... All of > these can significantly affect the area metrics you compile for each image > set. > > And that's all assuming that you can somehow thread the data of the > respective image layers that are served up via Google Earth, into an > appropriate image processing or GIS capture software array. In my opinion, > you certainly will not want to attempt the exercise within Google Earth > itself. While single point, line or polygon feature creation is supported in > the software, to attempt to extract large areas of adjacent feature layers > would be an extraordinary challenge (it's really not intended to serve as a > GIS, but as a simple "geobrowser" or tool to look at things). But if you have > access to software like ArcGIS, there very likely may be a way to gain access > to the imagery (often in a higher resolution and "clearer" version) as an > online feature or map service which NYS and other agencies host. > > How big is the area you are looking at? There are a number of satellite based > end products as well as potential input layers (e.g. Landsat) which, at 30m > resolution, you might be able to get some sense of the general trend (there > are also versions of certain products that measure change in land cover over > time...). > > -J > > John Mickelson > Geospatial and Ecological Services > 501 Stage Rd. > Monroe, NY 10950-3217 > (845) 893-4110 > [email protected] > > > ________________________________ > From: "Corbin, Jeffrey D." <[email protected]> > To: [email protected] > Sent: Monday, July 1, 2013 2:49 PM > Subject: [ECOLOG-L] Canopy cover from GoogleEarth images > > > Hello Ecolog – My colleagues and I are studying the reforestation of a > reclaimed landfill - from essentially bare-ground to a reasonably dense > forest from 1991 to present. I am interested in quantifying changes in > percent canopy cover over time using GoogleEarth images. Their archived > images include good–resolution growing season photos taken in 1995, 2001, > 2005, 2007, and 2010. Does anyone have suggestions as to how to quantify > canopy coverage in each photo? > > Many thanks! > > -Jeff > ________________________________ > ************************************ > Jeffrey D. Corbin > Associate Professor > Department of Biological Sciences > Union College > Schenectady, NY 12308 > (518) 388-6097 > http://jeffcorbin.org > ************************************ > ________________________________ > >
