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Answer for tclikesbigtrees on measuring tree height

Posted: Sat Jan 04, 2014 12:44 pm
by dbhguru
tc (from New Jersey),

Since you're becoming a good contributor to the BBS, your question on how to measure tree height without climbing the tree deserves an in-depth response, and other newcomers may have the same question, as well. So, this post will be for those who have recently joined the BBS, but don't have the time to wade through the thousands of communications to get answers to specific questions.

Measuring tree height is described well in Ed Frank's Wikipedia article. Ed did yeoman service on all our behalves in taking our scattered posts and documents along with other material and making a coherent description of tree height measuring. One of the Wikipedia source documents Ed uses is Will Blozan's guide to measuring trees, which John referenced. Alternatively, were you to just take pot luck and google "measuring tree height", you'd get a bewildering deluge of material and a mind boggling, virtually useless, display of highly repetitive diagrams. Avoid that!

If after you've read Ed's Wikipedia article and/or Will's guidelines, you have questions, we can answer them, but in the remainder of this post, 'll give a quick overview from a top down perspective - a glimpse into tree height measuring.

There are at least 11 different methodologies/techniques for measuring tree height in use today.

1. Method of similar triangles: This is widely used by champion tree hunters and is described in many Internet descriptions. The method can get you into the ball park, but the sources of error are hard to control - contrary to simplistic Internet descriptions. Nonetheless, the method of similar triangles is a useful technique to learn if you have minimal equipment. Ed Frank's Wikipedia article covers this method well. Were you to go to American Forest's website, this would be the method for measuring tree height described.

2. Traditional tangent method: This is also commonly described as the tape and clinometer method and it is the most prevalent technique used by timber specialists. It has its place in the measuring toolkit, but is misused a lot. It is implemented in advanced hypsometers as the primary tree height measuring routine. However, the hypsometer version does not fix the major problem with the method - an incorrect baseline for the top of the tree. Unfortunately, descriptions by manufacturers mislead users into thinking that their 3-point, tangent-based hypsometer method takes all relevant factors into consideration. It is just marketing. For the sake of one's wallet, the traditional tangent method can be used with several iPhone apps.

3. Sine method: This is the bread and butter method of NTS and the most accurate of these first three. Virtually all the tree heights listed on the BBS are based on this method. Any of a good dozen people on this BBS can instruct you in its use. Ask and ye shall receive.

4. Hybrid sine-tangent method: This uses the sine method for the top of the tree and the tangent method for the base. It is intended to solve the clutter problem in some situations, such as a tree with a visible top and a trunk buried in mountain laurel. The eye may be able to distinguish where the base is, but it can't be hit with a laser.

5. Cross-triangulation tangent method: This method is described well in Will's guidelines and solves a major problem that frequently occurs with the traditional tangent method. It is more labor intensive than the traditional tangent method.

6. External baseline method: This method gets almost no use, but has potential where the sine method cannot be acceptably applied and getting to the trunk of the tree with a baseline is not feasible. This is a method that I developed. It is described in SAF's April 2012 edition of The Forestry Source.

7. Parallax method: This is another method that gets virtually no use, but has its place. Michael Taylor and I developed it independently. I expect surveyors have long had their version of it. The parallax method requires very accurate input measurements. Like #4 above, it uses an external baseline.

8. Three triangles method: This is a potentially extremely accurate, computer program driven method developed by Michael Taylor. It requires very accurate inputs and uses three connected external baselines, but can be applied to trees at great distances. This method is not for the feint-hearted.

9. LIDAR: This is a high tech method that requires software and expertise. See Ed Frank's Wikipedia explanation.

10. Surveying Transit: This is more about the equipment used than the method since it employs high precision instruments to apply one or more of the above techniques.

11. Climbing with tape drop: As you would guess, climb a tree and dropping a tape is still considered the ultimate method of measuring tree height. However, given the improved accuracy and clutter penetrating ability of instruments like LTI's TruPulse 200X, climbing may not be any more accurate, but climbing will likely remain the acid test.

I should point out that measuring tree height is most commonly done in forestry, primarily for economic purposes. Big tree hunters who submit their nominations to either a state coordinator or the national coordinator are probably the second largest group measuring tree heights. Canopy researchers are becoming a significant group of tree height measurers, and I expect that climate and environmental scientists are beginning to join the ranks for very different purposes. Without question, NTS and associates are the most important sources involved in developing better height-measuirng methods to be applied to individual trees, as opposed to stand averages.

You will see posts on equipment testing from Karl Heinz, Matt Markworth, myself, Will Blozan, Jess Riddle, Michael Taylor, etc. We may be testing fairly expensive equipment, which could be discouraging, were you to think that you must purchase at the high end in order to do a good job. But you can get very good results for an out-of-pocket cost of as little as $250.00. Keep the Nikon Prostaff 440 in mind. I think you can still get used ones on Ebay.

Hope this helps.

Bob

Re: Answer for tclikesbigtrees on measuring tree height

Posted: Fri Feb 07, 2014 12:16 am
by tclikesbigtrees
Thank you for that information. This is the first time that I saw this. I normally only look at topics under each of the states. Today I decided to look at this.

Re: Answer for tclikesbigtrees on measuring tree height

Posted: Fri Feb 07, 2014 7:50 am
by Joe
tclikesbigtrees wrote:Thank you for that information. This is the first time that I saw this. I normally only look at topics under each of the states. Today I decided to look at this.
TC, suggestion- from within the list of all topics, on the right, click on "mark all read"

then each time you want to see new topics- click on this link: http://www.ents-bbs.org/search.php?sear ... nreadposts

that's the method I figured out, though I'm sure there are other methods to keep up with discussions--- when I see the list of new topics, I then click on only those which catch my attention-- I have that link saved to my desktop

Joe