More Accurate Tree Heights With The TruPulse 360B
by Jon Aschenbach
The use of laser rangefinders has greatly increased the accuracy of measuring tree heights.
They are fast, allowing us to make more measurements in less time. Still it is important
to use them carefully and properly.
The normal tree height measurement built into most laser rangefinders is the three point
height method. In this method, the forester shoots the tree anywhere on the bole, where he has a clear shot.
This nails down the horizontal distance to the tree. Then the forester shoots the top and bottom of the tree,
recording only the angles of the last two shots. The height algorithm built into the laser calculates the height
based on the horizontal distance and the two angles. This works very well on trees without lean and on trees
where the forester is quite a ways back from the tree.
To achieve the best possible accuracy in measuring tree heights, the forester should try to be far away enough
from the tree to keep the upper angle to less than 45 degrees. On level ground, with a tree 100 feet tall, the
forester should be roughly 100 feet back from the tree or more. When angles exceed 45 degrees, any lean present in the tree can throw the height measurement off. The problem of tree lean is more serious as the forester
gets closer and closer to the tree. If the tree is perfectly straight up and down, distance is not as much of a
problem. Unfortunately, trees seldom grow perfectly straight.
Here is an illustration of the potential problem with the three point height method:
e
on
Horizontal Distance
Angle tw
o
An
An
e
gl
gl
eo
ne
Recorded
Tree
Height
Horizontal Distance
Angle tw
o
Another method of measuring the heights of leaning trees is to use the Missing Line Mode with the TruPulse
360B laser rangefinder. Using the Missing Line Mode, the forester shoots target one (the top of the tree) and
then target two (the base of the tree). The TruPulse 360B calculates the slope distance from target one to
target two. This is the tree height and it is accurate whether the tree is leaning or not. It does not
matter which direction the tree leans.
SShhooot
ot to
to TTar
arg
get
et 22
Sh
oo
tt
o
t1
ge
r
Ta
to
t
oo
Sh
Ta
rg
et
1
Here s a diagram of how the Missing Line Mode works for tree height:
Shoot to T
arget 2
The Missing Line Mode is one of many options available on the TruPulse 360B. Additionally, the
TruPulse 360B includes a built-in compass and it can measure slope distance, horizontal distance,
vertical distance, tree height with the three point method, azimuth, and inclination. All measurements can be send to a Pocket PC using Bluetooth, so there are no cables to get in the way.
For more information on the TruPulse 360B, please call Jon Aschenbach at 503-707-6236 or email
at [email protected].
Next month, I will have another article on using the TruPulse 360B for measuring Crown Ratio,
Crown Radius, Tree Diameter, and other measurements commonly needed by Arborists.
Resource Supply, LLC
11607 SW Winter Lake Drive
Tigard, OR 97223
503-521-0888
Cell: 503-707-6236
Fax: 503-536-6869
www.resourcesupplyllc.com
Copyright 2008 by Resource Supply,LLC