LiDAR vs. Ground Truthing

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#1)  LiDAR vs. Ground Truthing

Postby Matt Markworth » Tue Jul 05, 2016 10:25 pm

NTS,

Here's a quick comparison of LiDAR-derived heights vs. Trupulse 200 ground truthing for ten open-grown oaks on flat ground. This can be a useful tool when trying to get a rough height estimate of a tree that can be isolated with LiDAR, especially for trees on flat ground.

For these ten oaks, here are some of the contributing factors that affect the accuracy of the LiDAR-derived heights:

Factors that favor accuracy
- Flat ground.
- These oaks are open-grown and fairly old, and are not putting on much height. From year to year some may gain a little, while others lose a little. As a comparision, older LiDAR files wouldn't be very helpful for younger forest-grown trees putting on a lot of height year to year.

Factors that don't favor accuracy
- The LiDAR files I used from the Ohio OGRIP site are about 10 years old.
- Some of these trees have sparse or broken tops, and may not provide a great surface for the LiDAR laser bounce.

For these ten oaks, all of the Trupulse 200 heights were higher than the LiDAR-derived heights, except for one tree. The biggest difference was 5.8' and the smallest difference was .2', with an average difference of 2.6' - that's not too bad.

The shorter LiDAR heights may be attributable to growth over the last 10 years and also attributable to the fact that some of these trees have very sparse tops that didn't fully get captured by LiDAR.

Again, I stress the importance of being on flat ground to attain numbers this close.

               
                       
tp200 vs lidar.JPG
                                       
               


Photo and LiDAR image of the 69.5' bur oak:

               
                       
IMG_6479.jpg
                                       
               


               
                       
lidar bur 2.JPG
                                               
lidar bur 2.JPG (21.28 KiB) Viewed 399 times
               
               


Matt

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#2)  Re: LiDAR vs. Ground Truthing

Postby Don » Wed Jul 06, 2016 3:32 pm

Good work Matt!
In addition to the environmental conditions you've included for LiDar, I'm wondering if the conditions that affect the TruPulse, ie, overcast vs. clear sky, etc.?
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#3)  Re: LiDAR vs. Ground Truthing

Postby Matt Markworth » Thu Jul 07, 2016 7:30 pm

Thanks Don,

I've never ran a thorough test in various weather conditions with the Trupulse 200, although I've noticed the Nikon 440 seems to acquire a target easier than the Trupulse 200 when a slight fog is present.

This particular day for the oak measurements was warm and sunny. In general, I try to avoid shooting directly into very bright sunlight to acquire the target easier.

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