Survey Under Tree Canopies

Hello all,
I am a beginner to the Reach systems, so my apologies if I am asking obvious questions…

What are the best practices when surveying underneath tree canopies?
My end goal is to be able to have accurate (~1m error) tree locations in a forest plot.

I have access to a Emlid RS (RRS-1), and a Emlid RTK GPS Module with a Antenna Factor Series SH High performance GPS antenna…
Currently, I have only been able to get “single” solutions, but I would prefer “float” if at all possible.

Is it possible/be better to set up the Reach RS in an open field ~1.2km away with good sky view, and take the RTK Module into the woods? If so, what setup/settings would I need to get “float” points?

What other information would be pertinent for you all?

Robotic Total Station, have Jolly Green Giant open the canopy up or burn / chop the trees down (what do we need them for anyways?) ; )

GPS / GNSS needs good clear view of sky to work.

Could I leave the Reach RS ~1.2km away in an open field while I take the RTK module into the Forest?
Will the two units remain connected?

Not sure it works that way… the ROVER (your Reach antenna) has to also have clear view of sky to triangulate. SInce you only have one Reach RS the other doesn’t have LoRa radio to communicate so have to use another form of communication connection. i.e. tcp, ntrip but even if so, no clear view of sky.

The base would be fine obviously. You can always try it to see if you get sufficient accuracy.
I think there is a limit to the antenna height… obviously you couldn’t get it as high over the canopy. Drone? But again, I think a limit to antenna height.

maybe others will REAL knowledge will jump in shortly. Might be able to use “other” methods to OFFSET? But maybe crazy mess. TB_RTK has a thread on something like this with a DISTO.

not sure even FLOAT will get ~1m accuracy also.

here is a great source for information:

Hi @spiwakd

Hope, this thread will help you.
TB_RTK did something like this.

For some reason I am thinking maybe Mapit app has support for some laser rangefinder to work in unsafe or trouble areas? I thought I saw that somewhere?
Maybe check that app out either way for your tree survey application?

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Did try with Leica, but it would not recognize the device. Anyway. its easy to just fill the distance from the laser and have Mapit calculate the bearing for you.

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Wow, thank you all for your answers this is a big help. Amazing Community

A few questions…

I saw this post awhile ago. A four meter pole would be nice, however our canopy height is ~30m tall trees. So that is problematic.
I will however try the use GPS only method. Wouldn’t this error be ±5m? Is it possible to get <3m?
What does @mdgps mean by about “SNR/MP-EL plot” and select the >40?

To calculate the distance to the points for the offset, would I need line of sight? That can be difficult sometimes in the forests around here.
MapitGIS does look handy though… I will have to do more research!

Would changing my Hz rate help at all? I have it currently set to 1Hz with GPS+GLONASS+SBAS+QZSS

My apologies if I am making this difficult, I understand that this is not optimal for this system, I just want to get the best data I can. Thank you all for your help so far.

Without seeing the forest i would say bringing any gps into the forest is no good.
How visible is the ground under the canopy from the air?
How many points on the ground? every 5m or so? or just random dots here and there?
Have you thought of mapping the ground from the air?

To be honest, during full leaf out, not really. Except for the occasional opening in the canopy due to a fallen tree.

75 Trees/Points, randomly dispersed throughout the forest plot

Yes. We have LiDAR data for the area, as well as RGB for the area.
That being said, we would also like ground data independent of the LiDAR and the RGB so that we can later compare how effective each method is.

So…My best bet would be to raise Rover as much as possible? With these settings?:
Positioning Mode: Static
GPS AR mode: Fix-and-hold
GLONASS AR mode: Off
14Hz GPS

You might as well just use your cell phone GPS then.

Your best bet for the accuracy you need is total station. RTK GNSS is ideal for clear open sky view, not covered.

I have no idea here, but can a drone with Reach RTK (base in open field) survey by hovering over each tree? Not sure how you would handle elevation though? Seems would still be difficult. Seems you still need to be at ground, measure diameter of trunk and offset measured point to center of trunk? I.e. total station with FieldGenius or similar?

How bout this?

TB_RTK’s idea with Mapit angle bearing and laser distance would be cheapest.

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How about a 60foot telescoping pole?


Reminds me of this thread:


isn’t there a ARP height limit?


Thank you for the suggestions, I will look into getting a pole to hopefully get a little higher into the canopy and see if that helps out at all.
Time to open another thread!

gonna sway in the wind way up there… even if no wind… better get tension on it.

I will add to this that I have used Emlid Reach RS with Topcon Total station. In this case you could set up your total station and combine laser with gps and work your way under canopy.

Since I wrote this article I just quoted, Emlid has become better integrated with Topcon, so it’s not necessary to use another software (Field Genius, etc).
Of course, this isn’t a “cheap” alternative, but at least there are a lot of savings on the GNSS equipment from Emlid.


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