Comparing two data sets.

NEV
NEV Global Mapper UserTrusted User
in Elevation Data

I want to create a DEM of a now submerged and buried Pleistocene surface. I have two data sets: 1. A Global Mapper DEM high resolution of the seafloor from MBES i.e. present bathymetry. 2. A contour data set from a Sub Bottom Profiler (SBP) reflector (0.5 m intervals from 0 to 6 m) showing the depth below the present seafloor of a defined "erosion" surface. i.e. the base of the overlying sediment. The contours therefore show the thickness (isopach) of the residual Pleistocene material and are effectively a mirror image of the underlying surface.

To reconstruct that palaeo-surface in actual space, I need to subtract the SBP thickness from the depth surface (bathymetry). I can do it for individual profiles (generated by GM Path Profile and processed in Adobe Illustrator) and attached below - but I want to be able to do so for the entire area of many square km that would require hundreds of such transects. The example shows greatly exaggerated profiles across the subject area: 1. seafloor (depth); 2. isopach (thickness of unit). Vertical and horizontal scales and exaggeration factor are the same in both profiles.

Bathy&Isopach_profiles.jpg

Best Answers

  • bmg_mike
    bmg_mike Global Mapper Guru Moderator, Trusted User
    Answer ✓

    You should be able to use the Terrain Analysis -> Combine/Compare Terrain Layers menu option to subtract one grid layer from another to create the result that you are after.

    Thanks,

    Mike

    Global Mapper Guru

  • NEV
    NEV Global Mapper User Trusted User
    Answer ✓

    Mike ...the evergreen...as David McKittrick writes in his history of GM, "the stuff of legend! Thank you. Your first (and invariably correct) answer to me goes back to GM V07. Your solution has jut worked by the way.

    Very best wishes.

    Nev

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