Sure, no one will really see this. But maybe the few people who visit here once a month will find it interesting. I've been playing with this stuff lately and I think it's pretty cool. Lidar measures reflected light to collect data, creating three-dimensional models from those reflections. There are many applications for this technology, but what I'm particularly interested in is forest canopy mapping, especially for height. I am involved with a group that searches for and measures trees and forests at their various potential maxima; for mass, height, range, etc. Lidar is a very effective tool for finding tall trees, and depending on the resolution, can map individual canopies. Lidar has been used successfully to find new supertall redwoods in California and Eucalyptus in Tasmania.
We've been using it lately to look at some forests in the eastern U.S.
The first thing you need is data; unfortunately much of the country is either unmapped or the data is available for money. I'm lucky that nearly the entire state of North Carolina was flown a few years ago and the data is freely available online.
The next thing you need is software to process it. It can be run through ArcGIS and some other programs, but luckily the US Forest Service has created a free program suite of Fusion and the Lidar Data Viewer (LDV) to view the data, along with an online tutorial.
It takes a little time to learn how to create usable files using the command-line interface, but after some reading and with a little help I was able to produce some usable output.
To test it out, the first area I downloaded data for was the area around my home.
The selected area in the image is my property where I've already measured a number of the trees, so I could verify the data. The LDV pulls up an image, in this instance colored for height and shaded with the range of heights. There are sometimes negative returns from scattered or reflected light.
You'll note the cluster of taller trees. This is because the area around was logged recently, except for my property. These are rather large and fairly tall trees for their age (app. 146 feet at 80 years), but not approaching the maximum for the species.
Here's the ground image with the canopy removed:
You might notice the logging roads above my property. It's even possible to see a few of the large boulders on the ground image.
Since I got it somewhat figured out, I've turned my attention to a nearby park; a few other people are doing the same. It's interesting that most of the tallest forests on productive sites in the Southern Appalachians are second-growth; after being clearcut the regrowth is dense, causing more elongation in competition for light, and the mostly even canopy has little texture for wind to enter so the trees protect each other. Since we've started looking, we've identified a number of other sites with potentially tall trees. A couple of people ground-truthed one spot and verified it to have the tallest known deciduous tree in the eastern U.S. (out west there are six species that are known get over 300 feet tall— In the east over 170 is really tall and only 4 species have topped it). Interestingly, this site was old-growth; while old-growth trees can get very large, many years of storms and weathering usually create complex and somewhat shorter canopies. Topography of the mountains in this area seem to have protected these trees exceptionally well.
Another large tree nearby had been previously measured and identified as a very tall, large old tree. Here's how it shows up in lidar:
Here's a matching aerial view
Perusing the lidar data shows other trees in the area, like this one:
You may be able to see the scale on the left indicating a height of nearly 175 feet. Here's the matching aerial view:
We'll be exploring this area in a few months. But there are many places we'll be going there that we would have skipped before. I'm excited to see what we find. |
