There is also in progress at some airports a procedure to use transponders not just to respond/ident to radar interrogations on the ground, but are used in a “multilateration” system to provide a surface movement system. (KSDF – Louisville, Ky., for example). This surveillance system uses triangulation from multiple sites to pinpoint aircraft and/or vehicle position for a surface map. The KSDF system also uses transmitted ADS-B data from aircraft and ground vehicles.
I have read, but cannot confirm, that the AMASS system requires use of transponders, but cannot confirm this (CJ Driver – do you know anything of this?).
Great, informative thread.