A transmitometer is an instrument used to measure the transmission of electromagnetic signals, particularly in relation to weather conditions such as fog or smoke. It works by sending and receiving signals to determine visibility and the presence of particles in the air that could disrupt the signal.
for measuring visibility on runways v use tranmissometer
Most airports now rely on automated weather systems that include a "forward scatter sensor." This instrument produces pulsed flashes of blue light, some of which is scattered at an angle toward a nearby detector. Visibility is estimated from the intensity of scattered light, which increases when there are more fog droplets, smoke or haze particles, raindrops or snowflakes in the beam.A second device is a transmissometer, which allows a more direct approach as it measures the capacity of a portion of the atmosphere to transmit radiation.