Terrestrial LIDAR

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dbhguru
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Terrestrial LIDAR

Post by dbhguru » Thu Aug 16, 2018 5:55 pm

Ents,

Tomorrow Dr. William Moomaw, Dr. Susan Masino, Ray Asselin, and I will host a researcher from UMASS Boston who will consider modeling some of the MTSF pines in the Elders Grove. Should be interesting. I'll report the results. It may portend a new mission for NTS.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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dbhguru
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Re: Terrestrial LIDAR

Post by dbhguru » Fri Aug 17, 2018 6:42 am

Ents,

The event I spoke about in the prior post on this thread will occur in a couple of hours. I have a few moments before Ray picks me up and we're off to MTSF.

Yesterday, I spoke at length with Dr. Eric Wiseman and Dr. Phil Radtke at Virginia Tech. The topic was a conference on forests and carbon sequestration that would involve all the stake holders. Involvement with the carbon issue has increased my awareness of how much information is floating around on the Internet accessible by the public that is conflicting. What's a poor farmer, hairdresser, florist, or politician to believe? Obviously, politicians from red states have used the confusion to sew the seeds of doubt about the authenticity of climate change as at least partly due to our profligate energy-squandering behavior. Industrial propaganda masquerading as science continues to hold sway with people. But there are legitimate questions about the role of trees in mitigating climate change that need better answers, more clarification. What do we know today, think we know, or expect to find out courtesy of the many avenues of approach to quantifying carbon in our forests, rates of acquisition, and overall trends?

American Forests is looking to play a bigger role in these debates. And NTS can be a participant in ground-truthing tree measurements. It is our one potential contribution that we can make better than almost all others. Sending graduate students out with tape and clinometers or even hypsometers to "verify" LIDAR measurements is a prescription for failure. However, so far I haven't heard a groundswell of enthusiasm from the membership for an NTS role. Beyond the faithful handful, are there voices out there in the wilderness yet to be heard?

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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Erik Danielsen
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Re: Terrestrial LIDAR

Post by Erik Danielsen » Fri Aug 17, 2018 9:05 am

Bob, I sure hope so- but I will acknowledge that the process of direct volume measurement with the reticle can be some hard work. It takes some practice to get the hang of, especially getting into hardwood crowns. For the newcomer getting started is no doubt the hardest part-

But! It is deeply rewarding, once the data starts flowing, to feel as though you've unlocked an entirely new dimension of big tree understanding, with great potential for new discoveries. Looking for taper (or lack thereof) becomes less of a point of novelty or suggestions of age, as you find that trees of similar dbh and height can have hundreds of cubic feet separating them in volume. New questions arise.

An unheralded little ravine in a local site shocked me the other day with a large array of extremely large hemlocks. The first I modeled comes to at least 520 ft3, in spite of being only about 100' tall. Only in Lilydale do I find other hemlocks over 500 ft3- not in Zoar, not in Allegany (yet), and I would doubt the adirondacks. You could say that 500 ft3 hemlocks are just as rare as some of our elusive wild orchids, or moreso. This is not the largest hemlock on site, either! But if it weren't for volume measurement, Hemlocks from 11-12'cbh and 100-110' tall would certainly not impress myself from a couple years ago as much as the slimmer but taller hemlocks that can be found at so many other sites.

I would encourage any member reading to give it a go.

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dbhguru
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Re: Terrestrial LIDAR

Post by dbhguru » Sat Aug 18, 2018 7:59 am

Erik, et al.,

Yesterday's outing was quite successful. Peter Boucher of UMASS Boston scanned Saheda, Sacajawea, and Ouray, and afterward, we agreed on a joint project to compare ground-truthed measurements from reticle data with computed values from the scan. I'll be frequenting the Elders Grove throughout September through December to get ever better three-dimensional profiles of the three pines.

Peter was mightily impressed with the Elders Grove and grateful for the opportunity to employ this advanced technology in the field. His colleagues have chosen distant sites, so he is aware that a site close to home could have multiple benefits. Doctors Bill Moomaw and Susan Masino were there witnessing the scan. Ray photographed the proceedings, and I provided comic relief.

We also discussed making film on the story of carbon in the trees. Obviously, the film maker would be Ray. Bill and Susan are solidly behind the idea and are sold on Ray's talents. I guess Ray is now going to insist that I buy the ice cream at the end of our outings. FAT CHANCE! His scoops debt from past outings is enormous. Simply enormous. He needs to get cracking and work it down.

Leading up top the meeting, I wasn't sure how well the venture would go, but it exceeded my expectations in that Peter immediately homed in on what he needed to do for a good three-dimensional reconstruction of the three pines and set about the task. He'll return at least once to pick up more points from higher in the canopy that can't be seen until leaf fall. I think he now fully appreciates the challenge of seeing through a 100 to 115-foot canopy of hardwoods and on to the top of a 172-foot broad-crowned white pine. You don't do it from a 100 feet away. Finding a tiny opening to what appears to be the highest points changes constantly as one moves farther back. We all learned that lesson early on. Keep fading back and the lower trunk is lost in ground-based foliage.

I'll report on the project regularly. Still hoping others of you will sign on. There's lots we can do together toward developing our sensitivity to trunk form, limb mass, etc. Erik, you made a hugely important when you mentioned the vast difference in volume that can occur between two trees with the same DBH and height. One begins to appreciate the compromise made by applying allometric equations that are based purely on DBH and height.

Bob

Between Woods Hole's interest and that of UMASS Boston and Harvard Forest, I think we've turned a corner. We are positioned better than ever before in getting topnotch academic-professional institution attention to places like the Elders Grove in terms of their carbon content and rates of sequestration.
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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RayA
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Re: Terrestrial LIDAR

Post by RayA » Sat Aug 18, 2018 10:30 am

Here are three photos of the Leica BLK360 lidar instrument operating during a scan. In the slot that's visible in the head of the unit (photo 1), there's a small mirror that rotates at high speed, scattering millions of laser pulses outward. In photo 2, the mirror in the slot is a blur, since it's rotating. Reflections of the pulses from objects in the unit's view create a "cloud" of data points that are stored in the unit, and in an attached laptop dataset. Each reflected data point represents a point on the surface of the reflecting object.

The laser unit itself rotates in increments atop the tripod, until finally a 360-degree (horizontally) scan is completed (takes about 3 minutes). The laser pulses cover about a 300 degree area vertically (according to the manufacturer's info), and out to a max of about 60m. The collected data points are used to create a black and white 3-D image of the scanned scene that can be played back on the computer, allowing the viewer to rotate the image around to see the 3D scene from virtually any angle.
InkedLidar 1_LI.jpg
Unit operating, mirror rapidly spinning
Unit operating, mirror rapidly spinning
Lidar 3.jpg

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Erik Danielsen
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Re: Terrestrial LIDAR

Post by Erik Danielsen » Sat Aug 18, 2018 11:20 am

Really interesting device. I assume that multiple overlapping scans along a grid can be combined in software to generate a truly 3-D model, as any given scan can only model the side of an object that's facing the device?

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RayA
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Re: Terrestrial LIDAR

Post by RayA » Sat Aug 18, 2018 12:52 pm

Erik,

Yes, they can stitch together a number of scans that give them a great 3D image. They can then move around thru the image as if they were walking thru the scanned area. The sample images I saw on Peter's laptop were black and white, and rather ghostly looking, but you can see bark detail, etc. While we were there, Peter moved the instrument to several spots around the trees to scan from different locations. At some point I may be able to get a sample video clip of the lidar scans, which we'll incorporate into a film. It's pretty cool technology.

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