What is a ceilometer used to measure in meteorological observations at airports?

• A. Cloud base height
• B. Wind speed and direction
• C. Precipitation rate
• D. Aircraft temperature

Answer: (A)

Ceilometer measures cloud base height—the distance from the ground up to the bottom of the lowest cloud layer. It works by projecting a light beam upward and detecting the light that is reflected back from the cloud base, allowing the instrument to calculate the height where clouds begin. In airport meteorology, knowing the ceiling is essential for aviation safety and is a standard part of METAR observations, reported in feet above ground level. The other options don’t fit this device: wind speed and direction come from anemometers and wind vanes; precipitation rate from rain gauges or radar; and aircraft temperature from thermometers on aircraft or surface sensors.