ex-rotaree......as nobody else has said....
ATM: Aerodrome Traffic Monitor. Effectively it's an air radar screen in the visual control room that's used by the Tower ATCO, but only for limited, specified uses.
The Tower ATCO might not have a radar rating, so it cannot be used as a surveillance radar to provide Approach Radar services.
Some of the uses might be:
- Determine landing order, distance from touchdown and spacing of arriving aircraft
- To aid in establishing separation in the event of a missed approach
- Identify, validate and verify SSR.
- Assist in taking initial corrective action if the final approach spacing becomes less than the required minimum.
....etc etc.