i used a pair of S1A IW VV GRD products for offset tracking. but after the dem assisted co-registration , the stack file shows nothing, both the master and slave amplitude band shows blank. why is this happening, i followed the offset tracking tutorial of sentinel 1 toolbox.
you can try to increase the number of GCPs and window sizes.
i was using aster dem but after i switched to srtm dem the problem solved, no idea why though