A certain air speed is required (to turn the weather vane, as it were).
While in ground effect, the air flow is different from the airflow in flight (away from the ground), so apparently a certain altitude above ground is required for the indication to be considered reliable.
However, I believe that it should be possible to recognise a sufficiently defective AoA sensor during the take off roll, and possibly in time to abort the take off. However, not sure whether pilots are briefed to do so, as that is a risky manoeuvre in itself, and a missing AoA sensor should not be any problem per se (in the absence of MCAS that is trying to kill you).
A certain air speed is required (to turn the weather vane, as it were).
While in ground effect, the air flow is different from the airflow in flight (away from the ground), so apparently a certain altitude above ground is required for the indication to be considered reliable.
However, I believe that it should be possible to recognise a sufficiently defective AoA sensor during the take off roll, and possibly in time to abort the take off. However, not sure whether pilots are briefed to do so, as that is a risky manoeuvre in itself, and a missing AoA sensor should not be any problem per se (in the absence of MCAS that is trying to kill you).