I have two maps in geotiff format for exactly the same area with exactly the same geoinformation. The first one is a real land map, the second one is a satellite picture with clouds (rgba where alpha is somehow the degree/thickness of clouds).

How can I combine these two maps so that the clouds are visible on the land map dependend from their transparency channel?

I tried gdal_merge but it does not use the alpha channel from the second map, i.e. there is no transparency but clouds fully overlap the other map. If I just open both maps together in QGIS, it shows exactly what I want.

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