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Snow - How to achieve a accurate DSM?

 Issue - Volume measurements of stockpiles are off by 5-10% (volume lower when measuring after a snowfall (about 2 inches) Images captured with drone. 

First project -  No snow. Capturing the images from 50m. Double grid mission and 80% overlap. Volume measurement result only 1,8% from previous traditional measurement method which were done with RTK-GPS.

Second project - About 2 inches of snow on the stockpile. Capturing the images from 100m. Single grid mission and 85% overlap. Volume measurement shows almost 10% less volume compared to the first project. 

Comments: I flew higher the second time since that the recommendation when the area is homogeneous. 

BTW, when I upload the same series of pictures to DroneDeploy the DSM looks better and the volume measurement is only 1-2% apart from previous measurement.

Questions:

  • Would the accuracy improve if the images are captured from a lower altitude?
  • Would double grid provide a higher detail of the DSM?
  • Are there some “tweaks” during processing in Pix4Dmapper which could improve accuracy?

DSM in first project. High level of detail. 

 

DSM from second project. Less detail. 

 

Thing is that now the measurement is within 1% from previous measurement. What I did was to add two manuell tie points. Re-optimized. Could it be that simple? DSM still looks a bit strange. 

Hi Anders -

General rule is that “Snow = No Go”.  

You’ll want to externally verify results either way, but I definitely would not rely on the set with snow in it. Not a good situation for photogrammetry. 

What camera would you use for volumetrics in snow? Photo? RGB? Thermal? Laser?

I don’t believe LiDAR works well in the snow either, but I don’t have any experience with that.