In my experience, the biggest problem with tree height surveys is being able to see the tops of the trees from the ground, and positively identifying which treetop goes with which tree.?ÿ?ÿ This is especially difficult if you can't measure a direct distance, since you have to identify each treetop from at least 2 different points.?ÿ If the trees aren't very tall, sometimes the best method is to locate the tree trunks and then run a 25' rod up into the canopy to directly measure the height.
I've done several hundred obstruction surveys to FAA standards. Both height and elevation were required on every one.
Does it depend on who has commissioned the work?
I've just had a quick look at the FAA guidance document and outside the airport boundary it appears to indicate that "area" objects such as woodland are divided into either 200 or 500 ft. grids and the "height" of the tallest object in each grid is shown. None of the diagrams appear to show ground height for the objects, just the top elevation. The accuracy specifications, from my quick reading, appear to be between 5 and 10 ft. with a resolution of 1 ft.
Given that trees grow, that appears to be sensible since there would be a time delay between survey and publication.
No doubt somebody who does these surveys on a daily basis can tell us all what really happens.
Depending on where this is, might the information already be available in a LIDAR database? Airborne LIDAR supposedly simultaneously discerns ground and canopy elevation, with fine spatial resolution. In some parts of the US, there's free online access to LIDAR data from Federal or state agencies.
How does one find if there is Fed or state info available in your area?
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The Hack
Depending on where this is, might the information already be available in a LIDAR database? Airborne LIDAR supposedly simultaneously discerns ground and canopy elevation, with fine spatial resolution. In some parts of the US, there's free online access to LIDAR data from Federal or state agencies.
How does one find if there is Fed or state info available in your area?
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The Hack
Given that for an obstruction survey you don't need tree "heights", just the canopy elevation then drone photography processed without any filtering should give something close to the upper leaf surface, probably around 1 foot below. Any of the regular software packages should give you this (and nobody is going to climb up and find out you have missed the odd leaf!).
That is what I am thinking right now.?ÿ Although the engineer is considering flying the project more old school.
In my experience, the biggest problem with tree height surveys is being able to see the tops of the trees from the ground, and positively identifying which treetop goes with which tree.?ÿ?ÿ This is especially difficult if you can't measure a direct distance, since you have to identify each treetop from at least 2 different points.?ÿ If the trees aren't very tall, sometimes the best method is to locate the tree trunks and then run a 25' rod up into the canopy to directly measure the height.
That is what I am fearing is going to have to be done.?ÿ Issue is the parcel is so darn thick, the ground traversing is going to take a ton of time, and cutting a bunch of undergrowth.?ÿ After that I am not sure my 25' rod would be tall enough, or I could see the top to make sure I was at teh same height.
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As to earlier (unquoted) posts:
- You were correct, I misspoke, I need canopy elevation, not necessarily tree heights - ie: do not necessarily need ground elevations.
- Existing data is not going to work, they need current data to justify taking a new tree cutting easement.
- Accuracy is 1' horizontal, 3' vertical.?ÿ I usually get it much better than that, but then again who is to say you are looking at the exact top of a tree when you are measuring it either.
- The Biltmore stick isn't going to work as I can't see the tree tops from the ground near them - same issue is not using a total station from the ground near the project.?ÿ
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I think if I can't elevate myself out of the canopy, then flying is the only option as there are trees that are not visible from any ground location that I can utilize.
Cut the trees down. From there is should be easy to tape 'em off.
Seriously, LIDAR is the way to go here. Both states I'm currently practicing in have freely available resources of that sort online.?ÿ I expect that most states do. The only question will be how recent the data is.?ÿ And if it isn't freely available for the area in question, it can be obtained via your friendly neighborhood aerial mapping service.?ÿ As a matter of fact, given the purpose, it would be a good idea to go the latter route.?ÿ
Do I understand you correctly? Two States that you practice in have freely available LiDAR data for the tops of trees and vegetation? Why would they have that?
You need a Bilby tower.?ÿ Unfortunately they are now scarce.
https://en.wikipedia.org/wiki/Bilby_tower
https://www.xyht.com/surveying/bilby-tower-dedication-honoring-jasper-sherman-bilby/
http://www.surveyorshistoricalsociety.com/osgood_wayside_marker.pdf
Billiby tower would be an obstruction. FAA not like.
What about a 45' reach bucket truck, and a scanner, and, a bit of ground control?
Or, 3 ladders, tied together, in a tripod?
N
@hack and @jamesfl ?? It was a couple of years ago that I was looking for LIDAR data for Massachusetts and Connecticut. I just now did a quick search, and I'm pretty sure these are the same sources that I found back then. They look like joint efforts of the states / NOAA / USGS. I have a recollection of seeing data for both tree canopy and bare earth, but right now I'm noticing only bare earth. I became interested in this after reading about University of Connecticut archeology graduate students using these data sets to rediscover stone walls and ruins of old farm building foundations.
Here are some links:
https://docs.digital.mass.gov/dataset/massgis-data-lidar-terrain-data
https://pubs.usgs.gov/fs/2014/3055/
Two States that you practice in have freely available LiDAR data for the tops of trees and vegetation? Why would they have that?
Here in WA, public agencies commonly contract for large-scale LIDAR collections as part of a consortium, and the full clean & classified point cloud is a key deliverable. The data is made freely available. The advantages to the agencies include having a mechanism for cost sharing, common quality standards for the data collected, and making the data available (and easily discovered) for reuse, including by members of the public.?ÿ
As an example, the dataset I'm working with most recently was a collaboration between the USGS and our state DNR, encompassing 3.6 million acres. The minimum density requirements are strict, as are requirements for ground control.?ÿThe metadata for some of the LIDAR collections in ~2000 or so have some really snarky comments about how bad the control was - a key point of the consortium seems to be avoiding this problem in the future through tight requirements.?ÿ
Full point cloud data is unbelievably versatile; top of vegetation, all vegetation at all elevations, hydrology, data on historical landslides and seismology, the ability to find old trails and road prisms in heavily timbered areas - or whatever else you want to use it for.?ÿ
Does MI have any data online? Their LIDAR program page is vague, alludes to "an exciting opportunity" in collaboration with the Sanborn Map co.?ÿ
- WA LIDAR Portal
- About the Puget Sound LIDAR Consortium?ÿ
- A great?ÿlist of state-by-state data
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Thanks Bill C
@Bill93?ÿ
A bilby tower is exactly what I need.?ÿ Doesn't have to be quite as stable, and isn't there for more than an hour.?ÿ I am just looking to make one out of construction scaffold instead of custom built.?ÿ And, I know I will not have a separate towner for the instrument - so I am wondering if it will be stable enough for an instrument setup - I think it would be.
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I've been in a bucket truck before, not stable enough for a survey instrument, but a decent idea.?ÿ And scaffold would be much more stable than makeshift 20-30' ladder setup.?ÿ I don't have the budget for a scanner setup.
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Mich lidar data is not easy to come by.?ÿ Maybe I am looking in the wrong spaces but I have searched all over the web.?ÿ I have not tried my state contact yet, but you notice there is no contact info on that project page.?ÿ I am still thinking it would be a miracle to have my rural area done over this last summer.
In any case, it would have had to be done this summer for accuracy, and client needs the dataset within a couple of months, so can't wait until next summer.
Set a few measuring poles painted like range poles plum within your group of trees. Then use your drone and verify your altitude and inventory the trees using the poles you set up to proof the tree's height.?ÿ A handful of poles wouldn't be expensive to make/measure or terribly time consuming to erect.
My .02 cents.
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Google up "Fodar".?ÿ Poor man's Lidar. Yours might be an excellent application and might open up other possibilities using your drone.
As I have only intermittently monitored this topic, I am confused. My first thought was that this was an ANA survey whose accuracies were copied in my previous post. I see refer to the stricter requirement of the FAA AC linked here:?ÿ https://www.faa.gov/documentLibrary/media/Advisory_Circular/150-5300-18B-chg1-consolidated.pdf#page152
I see numerous recommendations regarding regarding how to determine tree heights and positions. The acceptability of suggested methods is contingent on the required accuracy. Direct measurement of a tree still requires that the tree be located in some manner with respect to airport survey control.?ÿ
Browsing through the Remote Sensing Division??s material on the NGS reveals some very demanding specifications for the use of LIDAR in determining obstructions to navigable airspace. See:?ÿ https://www.ngs.noaa.gov/RSD/AirportSOW.pdf ?ÿ Has this SOW document been superseded or replaced?
As for the FAA AC, in reference to the original post I copy below a section detailing how one deals with a large grouping of trees. While this pertains to the charting, it implies to me that the bounds of the obstructing area be determined and that the most critical obstructions be determined.?ÿ
I claim no special knowledge. I am curious about what liability is incurred when performing these surveys? If I incorrectly determine the height and/or location of an obstruction and an aircraft strikes it and fatalities result, who gets sued?
I claim no special knowledge. I am curious about what liability is incurred when performing these surveys? If I incorrectly determine the height and/or location of an obstruction and an aircraft strikes it and fatalities result, who gets sued?
If the aircraft is so low that it hits the trees then it was going to hit something anyway. Nobody intentionally flies to miss obstructions by 3 ft.
Tie a 100' tape to your belt loop, and climb those trees. Once the tree gets too small to climb, then measure with a disto, to the TOP leaf...
then, tell the guy on the ground the plus, while he reads the tape.
Write it on a cardboard sign, at the base of the tree. This will be the description for the tree, while you tie it with total station, and data collector.
🙂 (Grin)
Distos are for wimps! Real men climb up there and use their 25' level rod to measure the tops.?ÿ
Theres nothing like being on 50 feet of "Un"-Safeway scaffold though, wobbling in the wind.?ÿ
My idea is unscientific. Measure the diameter and find a similar tree in the same bunch where you can observe it the normal way and call it the same. Good enough for a tree in the woods? Who, how and why would someone want to prove you wrong??ÿ
If the aircraft is so low that it hits the trees then it was going to hit something anyway. Nobody intentionally flies to miss obstructions by 3 ft.
Evidently you have never been in a helicopter piloted by a Vietnam vet...
