shadow measurements

General discussions of measurement techniques and the results of testing of techniques and equipment.

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Lucas
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shadow measurements

Post by Lucas » Mon Dec 21, 2015 1:55 pm

http://www.sunearthtools.com/dp/tools/pos_sun.php

Do sites like this that give light angles on given days make it possible to measure tree shadows with some accuracy?

I assume it is more complicated than it seems but it might be of some use.

I have a big red spruce I want to check.
We travel the Milky way together, trees and men. - John Muir

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Don
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Re: shadow measurements

Post by Don » Mon Dec 21, 2015 9:10 pm

Lucas-
Looks like you have all the tools in the attachment that you need...assuming that the ground that the tree's shadow is on is level. There can also be some 'wiggle room' involved with the particular satellite and it's images angle of incidence...it's quite likely that it wouldn't be looking exactly vertical down onto the tree's top...for example, if memory serves me, for your latitude, Landsat 7 would pass over your area around 10:30AM.
Don
Don Bertolette - President/Moderator, WNTS BBS
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dbhguru
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Re: shadow measurements

Post by dbhguru » Tue Dec 22, 2015 8:48 am

Lucas, Don,

There are always those cases where a measurement technique that relies on the principle of similar triangles works well enough. With the shadow method, crown size and the position of the highest spot in the crown relative to the location of the measurer, angle of the sun, and slope of the ground impact the result. If there are other trees in the vicinity of the tree being measured, shadows may be co-mingled. The simple stick method even with its limitations is usually preferable to using shadows.

Bob
Robert T. Leverett
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Lucas
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Re: shadow measurements

Post by Lucas » Tue Dec 22, 2015 11:38 am

Don wrote:Lucas-
Looks like you have all the tools in the attachment that you need...assuming that the ground that the tree's shadow is on is level. There can also be some 'wiggle room' involved with the particular satellite and it's images angle of incidence...it's quite likely that it wouldn't be looking exactly vertical down onto the tree's top...for example, if memory serves me, for your latitude, Landsat 7 would pass over your area around 10:30AM.
Don
The leaves are off and there is no snow so I was thinking of direct measurements, if I can get over there.
We travel the Milky way together, trees and men. - John Muir

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