I am looking for ideas to assemble a local positioning system for use in forests with decimeter position accuracy. Data rate should be 1 Hz or faster over a range of 500 metres.
We would like to position geophysical magnetometer measurements for archaeological prospection in a forest (where traditional positioning methods are very ineffective).
Which approach would you recommend?
Ultrasound based methods would presumably suffer in accuracy from multipathing/reflections from trees.
Would traveltime measurements of Wi-Fi or kHz signals be feasible?
Based on Wikipedia that might be the best course of action. On Wikipedia, if you read the “practical considerations” they use a UHF signal to obtain a relative positioning to a base station which has a RTK GPS receiver. If you just need the relative location you could probably figure out the UHF positioning system. Which I think is what the OP was leaning towards in the second part of the post.
RTK-GPS (we have 12 Javad receivers) would not provide sufficient position accuracy near or under trees due to multipathing. We get problems in open fields when we come close (20m) to the edge of a forest. Timing (pps) with cheap garmin gps receivers is an option though (e.g. to provide exact time stamps at bases and the rover).
If I understand correctly. You have a RTK-GPS system already (the Javad) and you’ve seen problems near the trees because they reflect the signal and screw with the calculations and therefore positioning.
So to overcome the distortion a high frequency signal suffers from the trees you need a low frequency device to “punch through” the trees. But the catch-22 there is that lower frequencies reduce the accuracy of phase time based positioning.
From a completely theoretical standpoint, could you use a low frequency wave as a sort of carrier signal to filter out the correct high frequency signal to use for positioning? Maybe that level of work and probably research is beyond what you had in mind. My grasp on positioning technologies is tenuous on a good day. So perhaps I’m out in left field, or “under the trees”, as it were.
I’m not sure I made myself clear GPS is of course only at the one frequency, but it’s not uncommon to use another type of RF positioning in surveying applications to establish a relative position based on the known and highly accurate RTK-GPS receiver. That secondary RF positioning system is a very flexible in terms of the usable frequency…well within the open spectrum. That’s what I was getting at when I was talking about using a lower frequency signal, not for the GPS but for the secondary RF positioning.
trueRF:
I’m not sure I made myself clear GPS is of course only at the one frequency, but it’s not uncommon to use another type of RF positioning in surveying applications to establish a relative position based on the known and highly accurate RTK-GPS receiver. That secondary RF positioning system is a very flexible in terms of the usable frequency…well within the open spectrum. That’s what I was getting at when I was talking about using a lower frequency signal, not for the GPS but for the secondary RF positioning.
I'm familiar with time difference of arrival (TDOA) and trilateration systems for positioning. And lasers. But not as accurate as RTK. And the TDOA systems I've worked with/seen are at 900MHz or 2.4GHz and need low multipath and near line of sight. Lasers as well.