I am using the gdal_merge python script to merge rasters that have slightly different, though similar, input resolutions. The documentation advertises that it can handle different resolutions, and in most cases, this works out reasonably well. However, I have had a few cases where the final merged raster looks significantly degraded, despite a relatively small resolution change (~10%). I first looked through the gdal_merge documentation to see if there were any options to set the interpolation method used to resample rasters whose resolutions change, but did not see anything. I then realized I do not even know what resampling method gdal_merge is using. How does gdal_merge handle resampling?
Also, if anyone has any thoughts on how to improve the results from using gdal_merge on rasters with different resolutions, I would be happy to hear those. I figured that would be a more challenging question though without providing many more details.