Tree Height Measuring Accuracy   Will Blozan
  Sep 26, 2005 14:40 PDT 
ENTS,

When discussing our tree height measuring accuracy, our sin+sin based
methodology will mean nothing, I mean absolutely nothing, without physical
verification of the actual tree height. That involves a tape drop. To the
average person our numbers are no more significant than anyone else's. We
have some numbers from our climbs but they are not displayed on our website.
We need a page to back up the credentials we say we have.

Maybe it's time we invited professionals to "tag-team" a champion tree that
we could get permission to climb. We could all measure it and discuss the
methods and pitfalls as a training session.

Will
Re: Lots a stuff   Edward Frank
  Sep 26, 2005 18:04 PDT 
Will,

I could not agree more.   The single most important thing we need to do in
order to upgrade the scientific demonstration of the effectiveness of our
tree measuring methodology is to compile a table of tree measurements taken
vie the laser/clinometer that were later confirmed by Will's (or others)
tree climbs. Until this is compiled our methodology is incomplete.

Bob wrote in a post on Sept 08, 2005: "At 66 feet my aging eyes saw the
scale just covering the trunk at a scale reading of 32.7 inches. Please
remember that I got this reading with the RD 1000 before I actually measured
the tree. I didn't want prior knowledge of the diameter to influence me in
settling on the scale width that just masked the trunk at the 66-foot
distance."

This demonstrates the need, even in our own minds, to show by a comparison
of measurements that the methodology is valid. A listing of all the climbs
is not important, perhaps twenty examples would be appropriate. What were
the measurements taken by laser before the climb and what was the actual
taped measurement taken during the climb. In some cases higher tops were
found in the climbs than were seen from the ground. Including some examples
of these with an explanatory note would be valuable in this context.

Ed Frank
Impulse vs tape drop in Borneo   Roman Dial
  Sep 26, 2005 22:39 PDT 

Will,

The Implse 200 LR was generally within 1 meter of the tape drop
measures. The tape drop measures were done by Tom Greenwood, who is an
international caliber competitive tree climber. The guy regularly
climbed to within 1-2 meters of the top! Now these Impulse 200 LR
measures were usually made by Brett, who's been doing big tree measures
for like 10 years (albeit usually with a Bushnell, a clinometer and a
calculator -- the humidity hurt his Bushnell). he took great pride in
estimating his tree heights as a conservative X+. He'd say "yep 82 plus"
using the laser and eyeballing midpoint of ground, then Tom would climb
and drop the tape and after adding the small bit at the top the number
would come out like 82.4 m. This happened all the time. We climbed 14
trees on our 14 day expedition (all over 65 m) and Brett was in all
cases but one (-2.7 m off) within 1.99 m and within 0.99 m for at least
2/3. In essence, Tom checked Brett's measures (underestimates when
lianas and woods tangled the view) and changed Brett's "plus" to a
point. So, to answer you question, Will, the Impulse in the hands of an
experienced user gives measures with 95% confidence intervals of 2 m (or
6 feet), and generally underestimate the true height by around 1 meter.

From my experience, the best pairing is a big tree hunter and a big tree
climber. I'd be interested to know if you folks back East have a
BVP-Sillett or Mifsud-Greenwood pairing?

Nevertheless, I think itís very important for the tall trees to be
climbed as it gives the most precise and accurate measure of the tree
height and more importantly the best view, looking down at the world
below after the pleasure of getting over difficult parts of the trunks
and forks.

Roman