The Electronic Area Scanner appears in the episode Operation Crash-Dive.
Carried aboard Thunderbird 1 to the west coast or Ireland, it was deployed by Scott next to a farmer's thatched-roof barn. Scott set up his Mobile Control Centre unit inside the barn (much to the chagrin of Kathleen, the cow occupying it), and monitored the scanner's progress tracking the position of the downed airliner Fireflash 4.
Scanner in lowered position.
Scanner in extended position.