Transmissometers are used to measure what?

• A. They measure wind speed along the runway
• B. They measure the runway lighting intensity
• C. They measure the extinction coefficient of the atmosphere
• D. They measure the air temperature near the surface

Answer: (C)

Transmissometers quantify how much the atmosphere attenuates a beam of light along a fixed path. They compare the light that leaves the transmitter with what the receiver picks up, and from that attenuation determine the extinction coefficient of the air. That extinction coefficient is the measure used to gauge visibility, which is why transmissometers are tied to runway visual range readings and weather visibility reports.

Wind speed is measured with anemometers, not transmissometers. Runway lighting intensity is checked with photometers or lux meters, not by assessing light extinction along a path. Air temperature near the surface is measured with thermometers. So the extinction coefficient of the atmosphere is the correct concept here.