In my case (I'm working in an area of Indonesian rainforest) even the coregistered data is not looking good, this is due the high temporal baseline of 12 days (in case of my Sentine-1 data). My coherence is too low, by around 0,3 for the vegetated areas.
But after I realizd this issues I was trying a test data about Pico de Fogo in Cape Verde, a vulcano with no vegetation, which was used in the SNAP TOPS Interferometry Tutorial (Veci 2015). I just wanted to know, if the phase to elevation tool is working in an area without issues due to vegetation, the coherence is much better here (displayed the stack as rgb and it is looking mostly yellow, so this should be fine) but the DEM results look just as bad.
I did the following steps:
-Interferogram (incl. coherence)
---Used a subset since here to reduce processing time
-Phase to elevation:
by way of comparison the real srtm for the same subset:
I also tried in the alps where not much vegetation should influences the coherence but the DEM was not better.
Thank you for your kind help!