This is a excellent idea. This certainly can be used where there is detailed enough imagery to do the measurements. Such detailed images are not available for everywhere. They are often available is urban setting, and less so in forested settings. With this option available doing spoke canopy spreads - averaging more than two diameters would give a better approximation of actual average crown spread. We are just beginning to explore the potential of the use of this detailed air photo imagery, and applications like LIDAR. I am sure it will revolutionize much of what we can accomplish. Crown spreads are one of parameters that is often undermeasured in the field. If the images are available it will allow people to measure them from their home computer.
Similarly GPS coordinates can be pulled from Google Earth if the specific tree can be identified. I did this for a series of trees I measured in a cemetery. I made a sketch map of the tree positions while doing the height measurements, and later pulled the GPS coordinates off an air photo of the area.
But for those forested areas of interest with high rez imagery, I can think of no better way of presenting the crown for measurement. Ed's comment on 'spoking' the crown, and yours at right angles are approximations and get close. At some point, I believe that the standard may be 'crown area' as measured by a "traverse" around the perimeter of the crown. The 2D area enclosed by the perimeter can be as accurate as the perimeter is drawn, and the most accurate measure of the crown (as is being considered by the AF's intent on crown measure.
Photogrammetry has been around for more than a century...with standards, ethics, substantial body of research already in place. Much more aerial photography exists than most people realize!
sfischer_16 wrote:I experimented with using Google Earth to measure the canopy of a silver maple. Google Earth has a measuring tool that is known to be accurate (http://bbs.keyhole.com/ubb/ubbthreads.p ... d=1#import)
Attached are two images showing that the canopy of this tree is 115' at its widest and 78' at its narrowest.
Seems like this could revolutionize canopy measurement, as it is simple, free, repeatable and verifiable. With experience ENTS could develop guidelines for correct usage to standardize it as a measuring tool. (In some settings the outline of the canopy might be hard to detect.) Note that the image includes GPS coordinates.
The address I used to search for this tree is 800 Cricket Avenue, 19003.
To download Google Earth, go here: http://earth.google.com
Give it a try (and verify my measurements)!
(By the way, this silver maple has a girth of 268". Still need to measure height, which I plan to do by sighting with a carpenter's square held against my cheekbone.)
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