UAV Aerial LIDAR Elevation Correction

I am still in the early phases of research for this project (LIDAR mapping), but are there any applications that can take data retrieved from a laser range finder and cross check it with a separate altimeter/IMU/GPS (Maybe barometric?) to determine the actual elevation, therefore factoring out altitude accuracy error of Ardupilot? I'm not completely sure whether I'll build the UAV to do this kind of LIDAR mapping, but I am considering the option of it. Thanks in advance.

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  • Scott,

    what you are suggesting is exactly what I meant. The RTK system would give an absolute level above a fixed datum then you simply deduct the height measured with the UAV from the height measured by the RTK system.

     

    You will not need any particularly special software to do the calculation. If you log the data as two different datasets then you can combine them later in a spreadsheet but they both need to be time-stamped and if using different clocks you need to synchronise them. The technique is very common in bathymetric surveys to allow for tidal variation and wave action on the vessel.

     

    Cheers,

    Mike

  • Thanks Mike and Chris for your responses. Chris, that Bushnell altimeter setup (and Bosch) would be useful although I'm not sure I'll be able to extract a sea-level elevation from that when I compute the actual terrain elevation to produce a map. However, I will keep it in mind when I am looking for a laser rangefinder to get terrain-to-UAV distance to subtract from sea level to get land elevation. Mike - that RTK sounds like the perfect system! If I could gather the data from the laser rangefinder (via RS232?) I could take the rangefinder altitude and subtract it out of the above sea-level altitude (From the RTK setup) to get the terrain elevation (if that makes any sense). Just curious, is there a computer program to combine these 2 data sets and subtract the elevations, or would I have to get that written? Right now this is all just hypothetical, but I see where this could turn into a decent business model. I think if my airframe (that I don't own right now) behaves as I have calculated on the computer (NexStar with some mods), weight of the equipment shouldn't be much of an issue but the lighter the better.

     

    - Scott Constantine

  • Scott,

    it all depends on your mapping specifications. Barometers will need correction for diurnal variation - even over a short flight - and even after the correction you are probably talking +/-1m at best plus your LIDAR error. The only real way to do this is with an RTK GPS system on board. If you have plenty of time there is an open source RTK system and there are some services I have seen online that do post processing 'RTK' from a single receiver on the aircraft but I think these services are geographically limited. Otherwise you are probably stuck with a faily hefty lump of electronics to fit in the airframe - and lift!

     

    Cheers,

    Mike

  • This may not directly address you're post...but I've been considering getting a Bosch DLrR130 laser range finder to make an altimeter enhancement.

    I'm currently waiting on a Bushnell x-band sports radar [in the mail] that i want to use for making an range finder / altimeter.
    I've been thinking about the possibilities of having Radar ranging + Laser ranging + Ultra Sonic + Barometric + GPS to fashion a very robust altitude measuring system that would work over any kind of surface. Sand, Snow, Ice, Water, Trees-Bush, Grass , rock, sand, bare soil, ect. wet or dry light or dark.
    The weight of the the Bushnell gun is 19 Oz, Probably without the two "C" cells.
    If the weight can be reduced substantially it may be practical, and I'll modify it to measure distance.
    .. otherwise, I'll just use it to clock my planes and I'll keep looking for inexpensive metalized plastic waveguides.
    There is also the Mattel Hotwheels toy radar gun. It's very cheap and much lighter, but the design is clever and it may work too. I'm just not sure how stable the oscillator is, though.
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