Which instrument is used to measure the extinction coefficient of the atmosphere?

• A. Thermometer
• B. Transmissometers
• C. Anemometer
• D. Barometer

Answer: (B)

Extinction coefficient describes how quickly light is attenuated as it travels through the atmosphere because of scattering and absorption. To determine it, you need to measure how much light makes it through a known path, not temperature, wind, or pressure. A transmissometer does exactly that: it sends a steady beam along a fixed path to a detector and measures the drop in light intensity relative to the emitted light. From that, you compute the extinction coefficient k = -(1/L) ln(I/I0), where L is the path length. In aviation operations, this data translates to visibility estimates used for flight safety. The other instruments measure different properties: a thermometer measures temperature, anemometer measures wind speed, and a barometer measures atmospheric pressure, none of which quantify how much light is attenuated.