Understanding Society User Support

I'm trying to reconcile income data from US with comparable data from the Family Resources Survey / HBAI 2009/10.

There are two household income variables in US hh_resp: a_fihhmngrs_dv and a_fihhmnnet_dv. These are described as 'gross' and 'net' household income in the past month - but not what the second is 'net' of (taxes? housing costs?).

I can't find is any further explanation, or description of how they are derived from the detailed income data - grateful for any help.