Laser measurement
The original question related to cloud on the ATIS. Those who have said it is measured by laser are barking up the wrong tree. A laser points straight up, so if there is a hole above it, it can report no cloud. As the ATIS is recorded by ATC, it is a visual assessment using experience, geographical points and where available comparing mode C readout with sighting the aircraft. The computerised ATIS systems can download METAR information but this is often edited.
40 years ATC, mostly towers.