Hello Johngan.
Actually, I find no detailed information about normalized angle in SNAP for Sentinel-1. But in SarScape, you can specify that angle to any positive value degree, and if value was negative, middle of angle is regarded as default reference (which quite make sense).
Here is SarScaple’s official help documentation:https://www.harrisgeospatial.com/docs/pdf/sarscape_5.1_help.pdf. In P769, you would find what I said above.
