IS ALOS POLSOR DEM need a pre-proccesing or correction?
Have you seen this tutorial on ALOS PALSAR orthorectification?
In case you are referring to the AW3D30: To a digital elevation it in SNAP (in the terrain correction step, for example), you have to reproject it in WGS84. But in general, they don’t need any geometric correction, because they are already in ground geometry.