True Pulse 200 Laser   Robert Leverett
  Sep 25, 2006 07:35 PDT 


   I reworked the earlier e-mail a bit and sent it to key people in DCR
and LTI. Hopefully, the LTI people will pay attention and eventually
work the sine top-sine bottom in as an alternate routine. Inch by inch
we are making inroads into the world of other tree measurers who are
fixated on tangent/slope based calculations. Perseverance will
eventually pay off.


TruPulse 200:

     On Friday a package arrived at Monica's house. It was my new
TruPulse laser
rangefinder-inclinometer-coffeemaker-backscratcher-toenail clipper.
After testing the model that Laser Technology Inc. loaned me a few weeks
age, I decided that I had to buy one for myself. So I put in the order a
week ago. On reaching Monica's house, Friday evening, I hurriedly
conducted a battery of tests with my new toy, as Monica call's it. I
conducted a second round of testing on Saturday. So far, I am very
pleased. The TruPulse that I received handles targets down to less than
1 foot away! That surprised me. I don't recall the test model shooting
such short distances. My TruPulse is virtually dead on at 120 feet and
less on about 2/3rd of the shots and within half a foot on the rest,
provided that the target is clear. However, it shoots a little short (1
to 2 feet) on long distances on about 2/3rds of the trials. However, I'd
rather be a little under than over.

     On the tests done so far on my instrument, the average of the
absolute differences between the laser and taped distances is 0.7 feet
on complex, indistinct targets (like the foliage at the top of a tree).
On flat highly reflective targets, the accuracy will likely prove to be
between 0.25 to 0.5 feet. There is a lot more to come on the TruPulse
testing in the coming weeks to include target differentiation tests.
This instrument is worth the testing.

     As a reminder to my prior e-mails, the 3 separate distance returns
to a target from the TruPulse are the straight-line or slope distance
(SD), the vertical height component distance (VD), and the horizontal
distance component (HD). You also get the inclination (INC). All these
returns come from one shot. You cycle through the readings with the down
button. This capability raises the efficiency of the TruPulse
enormously. To all these features, LTI still adds a height routine,
albeit the tangent-based one. However, there is a simple way around the
built in routine.

     Two shots to a tree with the TruPulse system set to the VD mode,
one shot to the top twig and one shot to the base of the tree returns
the two VD numbers needed to get the full height of the tree (provided
the highest twig was located). Add the two returns together and you have
the full tree height without the need for trigonometry. The height
calculating routine that Laser Technology predictably includes is the
tangent method. The routine requiresthree shots: an HD shot to the
trunk, the angle to the top and angle to the bottom. The TruPulse then
does the calculating and posts the tree height. But this method still
treats the tree like a vertical telephone pole in a level parking lot.
If LTI had included a simple routine just to add the two VD components
together, they would have built in the equivalent of the ENTS sine
top-sine bottom method. But regardless, LTI still gives us what we need
in the two VD returns. We become the adding machine. No big deal.

    I enthusiastically give the TruPulse two thumbs up. At $700, its
price is steep, but given all its features (it works with the RD 1000),
I think it is a good value. BTW, the trigonometric equivalents of the
TruPulse modes to our ENTS methods are as follows.


SD   = direct eye to target distance (They call it slope distance)
VD   = vertical component of SD
HD   = horizontal component of SD
INC = angle from eye to target.

   VD = (SD)Sin(INC)
   HD = (SD)Cos(INC)

    The key point to remeber is that you can be in VD mode when shooting
the target and then cycle with the down button through all the others
options for the one shot. What ever you measured in the VD mode is
locked in to the other modes so long as you don't fire the laser again
beforec checking the other values. In one test of my instrument, I shot
to what I know to be the highest twig of the silver maple in my front
yard. Shooting successively to the top and bottom in VD mode and adding
the two heights gave me 77.0 feet for the tree's height. I then put the
instrument in the height calculation mode and shot the trunk followed by
the top and bottom angles. I read the calculated result as 80.5 feet.
The HD mode showed the top twig to be a horizontally shorter distance
away than the trunk, as I knew it to be. In a set of future tests that I
intend to conduct, the results from both methods will be included, i.e.
the VD method versus the built in height method. If our past tests prove
true, the height difference between the two methods will average about 8
feet and the horizontal offset of the highest point from the base will
be about 13 feet.      

Striped Maple:

    On Sunday, I went to Mohawk to use the TruPulse. I had a feeling
that I might have a good day with the trees. Well, I did, but it wasn't
with the white pines or tall hardwoods. It was with the striped maples,
no less. I got a new northeastern height record at 65 feet – the
TruPulse’s first conquest! The following table lists the outstanding
striped maples that I've measured in Mohawk Trail State Forest.

Tall Striped Maples in MTSF
Hgt Cir DOM Location
65.0 1.7 24-Sep-06 Encampment G.
60.5 1.8 16-Jul-04 Encampment G.
60.3 1.6 24-Sep-06 Encampment G.
59.5 1.8 24-Sep-06 Encampment G.
58.3 1.3 11-Aug-03 Trees of peace
56.5 1.7 24-Sep-06 Encampment G.
56.0 1.7 24-Sep-06 Encampment G.
48.4 2.0 24-Sep-06 Encampment G.
47.2 1.9 24-Sep-06 Encampment G.

    Years ago, I measured two striped maple in Monroe State Forest, one
to 59 feet and the other to 57. The 59-footer was the height champ
prior to the Mohawk trees.

Question to Dale Luthringer:

     Dale, what's your best striped maple measurement in Cook Forest? I
would imagine that there are many striped maples in PA between 45 and
60 feet, a few over 60, and perhaps one somewhere pushing 70. Will
Blozan has the eastern record for the species in the Smokies, with one a
little over 77 feet! That is the same height as the 105-year old sliver
maple in my front yard. Jess Riddle may also have measured a super
striped. I can't remember.

       The new record striped maple for Mohawk is in the ENTS Grove. It
is skinny at only 1.7 feet around and grows under a tall white pine
canopy. There is plenty of air space for the striped maple champ. The
100-120-year old white pine stands appear to be where to look for the
record striped maples. The new champ has an injury at its base. I doubt
that it will live longer than 5 to 7 more years, 10 at the most.


Robert T. Leverett
Cofounder, Eastern Native Tree Society