Everett Woods-154.5' sycamore, Ohio ht. record

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Don
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Re: Everett Woods-154.5' sycamore, Ohio ht. record

Post by Don » Mon Feb 02, 2015 9:24 am

Stefan
LiDar is a wonderful tool, but it's not magically infallible. Essentially it relies on a sampling...you should imagine its "hits" as a grid, say 1 meter apart, and wherever on the tree it hits, is the reading you get.
The real value of LiDar is that of a filter, where whole acres can be filtered out from lack of superlative heights (LiDar doesn't yet by itself recognize species differences).
Don
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Steve Galehouse
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Re: Everett Woods-154.5' sycamore, Ohio ht. record

Post by Steve Galehouse » Mon Feb 02, 2015 7:29 pm

Stefan, NTS-

What's the point of even using Lidar data if it's so wildly inaccurate in determining tree heights? This is the first time you've questioned it's accuracy. You've cited numerous examples over the years on how accurate Lidar data is in comparison to actual rangefinder/ climometer readings with other trees, and now, all of a sudden, you're telling me it can be off by a factor of two meters. I've been a firm believer in LiDar data because of you. If I had known what you're telling me now, I wouldn't even have bothered learning the Fusion system.
I apologize if I've given the impression a LiDAR 'hit' is the actual height of a tree; when I first started using LiDAR and Fusion several years ago I thought of it that way, and would measure a tree until I found a value that approximated the 'hit'. As I became more familiar with Fusion I realized the 'hits' might not occur in the tallest part of the tree, since the returns are based on a 2 meter grid pattern for Ohio. I feel LiDAR/Fusion is very accurate at identifying tall trees on a site, but ground-truthing with laser and clinometer is necessary get an actual height, which might be lesser or greater than the LiDAR 'hit' due to terrain and crown characteristics.

Steve
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sradivoy
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Re: Everett Woods-154.5' sycamore, Ohio ht. record

Post by sradivoy » Tue Feb 10, 2015 12:58 am

Don, Steve

Thanks for the clarification. Hopefully one day soon the LiDar data grid can be whittled down to half a meter or less. I wouldn't be surprised if LiDar is more accurate with certain species over others just on crown characteristic alone. It's probably more accurate for hemlocks with their dense foliage on top versus broad leafs with their open branch work and empty space in between. It would be interesting to know how the LiDar "hits" of the other two 150' sycamores (one in hocking hills and the other California woods) compare to their respective rangefinder/clinometer readings. This would give me a better idea on how to interpret the LiDar data for this particular species in advance to an actual visit.

Stefan
Last edited by sradivoy on Wed Feb 11, 2015 9:48 am, edited 1 time in total.

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sradivoy
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Re: Everett Woods-154.5' sycamore, Ohio ht. record

Post by sradivoy » Tue Feb 10, 2015 9:39 am

The reason why I ask is that I've come across a promising 151 "hit" on a floodplain that appears to be a sycamore (not entirely sure). Based on 2007 data it may have grown some, and if the LiDar "hit" isn't the actual top even more so.

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Don
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Re: Everett Woods-154.5' sycamore, Ohio ht. record

Post by Don » Wed Feb 11, 2015 12:50 am

stefan-
Context is everything...I was introduced to LiDar as a tool for natural resource inventory, especially here in Alaska where much of our 'resources' are remote. LiDar was a good tool, but an expensive undertaking. Multi-phase sampling was an interim solution, running economic medium resolution strips with high resolution strips in between.

Better than 1 meter resolution is obtainable but at considerable cost, particularly in areas the size of Ohio. Usually such resolution comes with multi-agency collaboration and high-value landscapes.

So for many, LiDar is a great way to sample large areas, and serves as an excellent filter for highlighting tall trees. As to tall individuals of shorter species, it's a problem so far, as LiDar is a pretty coarse filter for species. Last I looked a few years back, folks were looking to co-register multi-spectral imagery with LiDar to improve species ID. Pretty space-agey stuff.
-Don
Don Bertolette - President/Moderator, WNTS BBS
Restoration Forester (Retired)
Science Center
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Jess Riddle
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Re: Everett Woods-154.5' sycamore, Ohio ht. record

Post by Jess Riddle » Sat Feb 21, 2015 11:01 pm

Another issue is that LiDAR measures canopy height while we measure tree height. If LiDAR returns a number other than the tree height for a tree on a significant slope, that discrepancy, strictly speaking, is not an error. LiDAR is useful to us, because tree height and canopy height are highly correlated.

Jess

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