1

I am working with a glacier and I want to get the Hypsometric curve of the elevation difference between two time periods. I divided the mask of the glacier by the contour lines (each 50 m) and now I want to extract the information of the raster with the elevation difference for each area that is between the contour lines.

My idea was by taking each one of the +100 polygons that are in the mask and exctracting the raster by each on of them, and then getting the statistic, but that seems like a very long step, and I have 24 more glaciers to analyse.

Does any one know a better way to do this using QGIS? Or also with R, but I am not so good in that last one.

I put an image with reference and with a part of the raster that was extracted. enter image description here

Improve this question

1 Answer 1

Reset to default
0

  1. Create a difference layer with the Raster Calculator, to get the difference in glacier heights over time, ie. Raster2 - Raster1. This will create a new raster layer

  2. Use Zonal Statistics on the new layer to compute the mean difference within each polygon.

Let us know if you get stuck.

Improve this answer
3
  • Hello, yes, the first step is the DEM I am using, and I want to know how much was the elevation difference in each elevation. I used the Zonal Statistic and it worked! I must select every object before and make the analyses then. Now is more easy, even though I still have to pass by hand the superior and inferior elevation given by the contour line of each area to make the hypsometric curve, but this is a great advance. Thank you!
    – Felipe Gomez
    Apr 23, 2021 at 4:51
  • If your contour data are in different layers, then merge them to a single layer first. That will save a lot of time. Calculate the difference between rasters, then run zonal statistics using a single merged polygon layer and a single difference raster.
    – wingnut
    Apr 23, 2021 at 5:12
  • Yes, you are right, I just tried that but the contour lines dont have the same geometry than the polygons with the areas. But I tried other thing that worked. I made the same that I did with the raster of the elevation difference (-5 m -10 m -15 m...), but now with the raster with the real elevations (2500 m 2550 m 2600 m). So the zonal statistic gave me the minimum and maximum of each area, from which I can deduce between which elevation it is the area and the media of elevation difference that was calculated before. Thank you so much for the help, and greetings from Chile! :)
    – Felipe Gomez
    Apr 23, 2021 at 5:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.