| Conference
report - Measuring Experiment |
Robert
Leverett |
| Oct
17, 2005 08:22 PDT |
ENTS,
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.
Bob
Robert T. Leverett
Cofounder, Eastern Native Tree Society |
|