Pixel DB values

Good day,

I have a question concerning the pixel values. In the workflow I convert linear to db, are these range of values normal for these images (first VH, second VV) or should make some other conversion? And is there a quick way to tell the difference between a VH image and VV image?

Thank you

  1. The values don’t appear to be normal - did you calibrate first?
  2. No quick way to tell in isolation. If you have both you should be able to figure out which one is which.

Hi mengdahl

Below the workflow used. I am using xml/gpt to generate the images.

How are the values in SNAP? Which format did you use for import/export?

I have posted another topic with this exact same question, I can´t open these geotiffs in snap. Could it have something to do with this?
The db pixel values are supposed to have negative values? I was checking in Qgis and they seem to be negative, couldn´t find any positive.

In SNAP you should work with the satellite products and not directly with the geotiff data layers inside them. Export to the format you need afterwards.

I just check with the histogram in Qgis and it seems to look fine, I think.
Could this mean it´s only a matter of adjusting the range of values? In Snap should be a lot easier to see this but can´t open, as mentioned before.

Open the output products of your processing-chain in SNAP and see if the values are correct there. Then export to GeoTIFF. You cannot assume the geotiff-files inside the products are fine to use as is.

I´ll try that and check the values. Thanks.

Good morning,

I ran the xml file in snap only this time changed for DIMAP format and it shows some different results.
In QGIS the range of values is much different.

Same images opened in QGIS:

They are the exact same image. Then when I convert to geotiff and open it in QGIS again a different set of values. (below, image with first file being the same file opened in QGIS, and the second a geotiff created from the same image).


Randomly I checked some pixels and they all have the same value, it seems the process is correct. Didn´t see any strange values. Could this mean that the pixel values are correct, the images were correctly generated? Or do I have to make some other verification?


they are identical, SNAP and QGIS differently estimate the min / max value.

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Hi ABraun,

Thanks for your reply.