I am a newbie here. I made a video of the descent and landing of flight F91678 RDU-SYR 2022-06-30 Thursday (Frontier). From the video, I can tell the moment the wheels hit the runway. I am trying to sync the video to the time of a day. The log gives Thu 10:31:42 AM when the altitude is 100 feet. Is the 100 feet the altitude above sea level or above the runway? Perhaps 10:31:42 AM is the best estimate I have for when the wheels hit the runway. Thanks. I don’t know much about aviation.
If you have a receiver and the aircraft is of a model to use it, believe there is a nose wheel 'on ground ’ switch that toggles a 0 to 1 and sends message type 5 instead
But digging it out from all the other signals may not be easy
That’s not quite correct.
There is speed limits also used and above a certain speed the transponder will continue sending “in the air” despite being on the ground.
So getting the precise point of touchdown is usually best done looking at the track and determining where deceleration starts and descending stops.
Barometric altitude (which is essentially “above sea level +/- difference due to current local air pressure”). note that it has a resolution of at best 25ft.