Artefacts appears on resampled Tiff DTED after performing an slope analysis

[poulet1212]

As input file I use a single band 32 Float geotif file with elevation data. I reproject it using gdalwarp like: gdalwarp -ot Float32 -co "tfw=yes" -dstnodata 0 -s_srs EPSG:21781 -t_srs EPSG:4326 src dest

The result seem to be good as first glance, but problems appear as i perform a slope analysis on tjhe resulting file with either arcmap or QGis. Look the two attached file:

• slope_analysis_without_artefact.PNG is the analysis performed one the original data
• slope analysis with artefacts.PNG​ is the analysis performed on the reprojected data. You can clearly see some artefacts on the image.

The same problem also appears if if resample the data to a bigger cell size.