What is "transmissometer"

n. An optical instrument used to measure the transmission of light through a material.

A transmissometer is an instrument for measuring the extinction coefficient of the atmosphere, and for the determination of visual range. It operates by sending a narrow, collimated beam of energy (usually a laser) through the propagation medium. A narrow field of view receiver at the designated measurement distance determines how much energy is arriving at the detector, and determines the path transmission and/or extinction coefficient. Atmospheric extinction is wavelength dependent phenomenon, but the most common wavelength in use for transmissometers is 550 nm, which is in the middle of the visible waveband, and allows a good approximation of visual range.

Transmissometers are referred to as telephotometers, transmittance meters, or hazemeters.

The term transmissometer is also used by oceanographers and limnologists to refer to a device for measuring the optical properties of natural water. In this context, a transmissometer measures the transmittance or attenuation of incident radiation from a light source with a select wavelength, often 660 nm, through a defined cell volume.