Conference report - Measuring Experiment   Robert Leverett
  Oct 17, 2005 08:22 PDT 


     Well, the 3rd annual event in the Forest Summit Lecture Series
enters the books as recorded history. It was successful despite mother
nature's attempts to drown us all. The lectures on Thursday and Friday
evening were outstanding (especially Lee's and Tom's on Friday).
Monica's Saturday evening concert was stellar, just stellar. Our tree
measuring experiment on Saturday in the rain was was nuts, sheer madness
- but fun and very successful. Well, there is a lot to relate about the
weekend. I won't attempt to do it all in one communication. In this one,
I'll first go straight to the tree measuring experiment.

     Our purpose was to test different measuring techniques against the
results of a tape drop for the Massasoit pine in the Pocumtuck Grove in
MTSF. The pine is a double that grows at the edge of a leaching field.
Its accessibility and visibility made it a good choice to model and test
three tree height measuring techniques: the sin top-sin bottom method,
the tan top-tan bottom method, and the method of similar triangles. I
had measured the tree the previous week by taking 11 separate sin-sin
measurements from various locations, simulating what a first time
measurer might do. I also took four tan-tan measurements. The unusual
results I got along with the tree's convenient location convinced me
that the Massassoit pine was a good choice. The apparent high point was
to the rear and right of the tree and that meant crown visibility would
be a significant factor in measuring the tree.

     The participants were Tom Diggins, John Eichholz, Howard Stoner,
Will Blozan, Ed Frank, Carl Harting, Susan Scott, Jess Riddle, and
myself, courtesy of the measurements taken from the previous week. A
10th participant, Craig McAuslin was involved in the similar triangles
measurement. Lee Frelich acted as observer of the event and I was the
recorder. I'll cut to the chase and post results. I will refrain from
identifying the individual measurers, except myself, and some individual
results of others.

Sin Method
Height Tape Abs(Diff) Diff
142.6 146.1 3.5 -3.5
143.1 146.1 3.0 -3.0
144.4 146.1 1.7 -1.7
143.5 146.1 2.6 -2.6
143.8 146.1 2.3 -2.3
144.0 146.1 2.1 -2.1
141.2 146.1 4.9 -4.9
143.6 146.1 2.5 -2.5
145.0 146.1 1.1 -1.1
141.8 146.1 4.3 -4.3
144.2 146.1 1.9 -1.9
146.1 146.1 0.0 0.0
144.9 146.1 1.2 -1.2
146.4 146.1 0.3 0.3
145.4 146.1 0.7 -0.7
147.8 146.1 1.7 1.7
146.1 146.1 0.0 0.0
149.0 146.1 2.9 2.9
149.1 146.1 3.0 3.0
144.1 146.1 2.0 -2.0
145.3 146.1 0.8 -0.8
145.6 146.1 0.5 -0.5
146.2 146.1 0.1 0.1
144.4 146.1 1.7 -1.7
145.3 146.1 0.8 -0.8
141.6 146.1 4.5 -4.5
142.0 146.1 4.1 -4.1
140.7 146.1 5.4 -5.4
148.6 146.1 2.5 2.5
148.4 146.1 2.3 2.3
148.0 146.1 1.9 1.9
146.9 146.1 0.8 0.8
143.5 146.1 2.6 -2.6
146.0 146.1 0.1 -0.1
145.9 146.1 0.2 -0.2
143.1 146.1 3.0 -3.0
Avg 2.0 -1.2

Tan Method
Height Tape Abs(Diff) Diff
140.2 146.1 5.9 -5.9
140.5 146.1 5.6 -5.6
133.7 146.1 12.4 -12.4
138.3 146.1 7.8 -7.8
133.9 146.1 12.2 -12.2
Avg 8.8 -8.8

Similar Triangle Method
Height Tape Abs(Diff) Diff
135.0 146.1 11.1 -11.1
146.0 146.1 0.1 -0.1
140.5 146.1 5.6 -5.6
174.5 146.1 28.4 28.4
135.8 146.1 10.3 -10.3
133.8 146.1 12.3 -12.3
Avg 11.3 0.0

Method Avg Abs Error
Sin 2.0
Tan 8.8
Sim Triangle 11.3

Please remember that the above experiment mixes results from ten
different measurers using different equipment from different locations.
Because of the rain, visibility of the crown was slightly obscured, but
didn't prevent us from measuring. Will's tape drop was assisted by
Howard Stoner and myself. The result of the tape drop was 146.1 feet. In
terms of individual results, I should note that Susan Scott's single
sin-sin measurement was 146.1 feet and the average of Will's five
sin-sin measurements was also 146.1 feet. John Eichholz's similar
triangle measurement was 146.0 feet. John had trouble with his
clinometer on the sin-based measurements.

   The average of my 11 measurements from the prior week was 145.0 feet.
So my average is 1.1 feet off the tape drop. A total of 47 measurements
of all classes were reported to me, including my own.

   Predictably, the tan-based calculations came up short because the
high point was back of the trunk. The straight line distance from the
tape drop line to the center of the trunk is 14 feet, i.e. the crown's
high point is offset from the center of the trunk by 14 feet.

   One other experiment was conducted. Will projected the top of his
pole with a target above the crown by between 1.5 and 2 feet. I measured
the height of the projected target at 147.8 feet. This appears to be
within +/- 0.2 to 0.3 feet of true height.

    We could have accomplished more had it not been so wet, but the
experiment did clearly demonstrate what we have been saying for years.
Next year, we can repeat the experiment with even more participation.
The leaching field provides a perfect spot to perform the experiment.
People can see the target and concentrate on measuring instead of jsut
remaining vertical, which would have been the challenge with the Joseph
Brant pine on those very steep slopes.

    The average of the absolute value of the difference of measured
results versus tape drop of 2.0 feet illustrates what we have been
saying about accuracy. With properly calibrated equipment and repeated
measurements, an experienced measurer can be within +/- 1.0 feet of true
height in the vast najority of cases. The 2.0 figure is more typical of
the average variability of different measurers using different equipment
from a variety of locations. I'm actually surprised that the difference
isn't a little wider. Note that the average of the differences (as
opposed to the average of the absolute values of the differences) is
-1.2 feet. The sin-sin method understates the true height - on the
average. At least this initial experiment points to that.

     Thanks to Will's superb climbing skills and his dedication to
measuring accuracy, we have a formula for conducting many height and
volume measuring experiments. We will put all this into a book.

      At the risk of sounding a bit contentious, in my usually not so
humble opinion, ENTS should concentrate on attracting expert tree
measurers into our fold, really serious dudes, as opposed to trying to
win acceptance from run of the mill champion tree list participants. If
we win acceptance from the latter, it should be because they come
courting us, not the other way around. To go after them is rather like
major leaguers seeking acceptance from little leaguers. It has the cart
before the horse. If that sounds elitist, I suppose it is, but then Ents
aren't just ordinary dudes. Hey, Pamela, it's your turn. How about
another paragraph of bad tree puns. Your last one was a beaut.

   As a final comment, Dale, Scott, Bob, Holly, Mike, Darian, etc., we
missed you all. Next year the event will be the last weekend in October.
Hope you all will be able to make next year. It's loads of fun. Pamela,
maybe you can make it out from Iowa, and Roman, Alaska's a long way
away, but you've got a spot reserved, if you can make it. More in the
next e-mail.


Robert T. Leverett
Cofounder, Eastern Native Tree Society