Attached is the worksheet that I developed for the advanced tree-measuring workshop scheduled for Oct 12th at Mohawk Trail State Forest, MA. I developed it around use of the LTI TruPulse 360 although a conventional laser rangefinder-clinometer-compass can be used instead. I set the worksheet up to take advantage of the TP360's features since Steve Colburn from LTI will bring a bunch of them to the Oct gathering for others to use. I would greatly appreciate it if NTS members who plan to come can tell me now so that we can try to have sufficient TPs available.
As I have often reported, the TP200 and TP360 are extremely accurate. I conducted a calibration test yesterday on my TP200 and on 4 trials had an average height error of a mere 1.9 inches. That's really good. However, I must point out that when I do calibration tests, I use a very clear target and I have to be able to measure its height with extreme accuracy, so the conditions are almost of laboratory quality. Otherwise, how do I know how large/small the measurement errors actually are? Measuring to fuzzy targets isn't likely to be as accurate, but there is good reason to believe that under the vast majority of field conditions, the accuracy of the TruPulse is within +/- 0.5 feet. Occasionally, you can be off by a foot. I'm assuming that the target is sufficiently distinct and visible to make measuring possible.
For those of you willing to wade through the worksheet, you'll notice that the sine and tangent methods are being compared. But also calculations are being called for that illuminate the reason for differences in results. The NTS faithful come to understand that measuring tree height is a problem of determining the vertical distance between two points in three-dimensional space. No assumptions are made about what might connect the two points, if anything. Dependency on a configuration that postulates a woody connection between the two points and the vertical alignment of the points is forever lifted. Thinking more abstractly and after a time, the thought of dependency on a trunk to connect the two points seems rather unimaginative, if not down right silly. However, if one is combatting decades of habit, going from tangent to sine does not turn out to be easy to do.
My solution is a step by step process that focuses attention on the two components of height (eye level to upper point and eye level to lower point). Hopefully, the worksheet, an explanation, and live exercises using convenient equipment will do the trick.Feel free to use of modify the worksheet to fit your needs. I view it as an NTS product.
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Robert T. Leverett
Co-founder and Executive Director
Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest