transmissometers

A transmissometer is an instrument that measures how much light is transmitted through a medium along a fixed optical path. It typically consists of a stable light source and a receiver aligned on a defined distance, with a detector that records the transmitted light intensity. By comparing the received signal to a reference, the device computes transmittance and, from a known path length, the beam attenuation characteristics of the medium. Transmissometers are used in fields ranging from oceanography to atmospheric science and civil aviation.

In oceanography, transmissometers quantify water clarity by measuring the amount of light that passes between a transmitter and receiver separated by a standard path length, commonly several meters. The ratio of received to emitted light is converted to transmittance and to the beam attenuation coefficient, linking measurements to turbidity and optical properties of the water. Infrared or visible wavelengths are typical, and data are used to monitor coastal water quality, sediment plumes, and daily variability in visibility for research and operations.

In atmospheric and civil aviation contexts, transmissometers monitor meteorological visibility along fixed paths, such as runways. A collimated beam is directed toward a receiver, and the measured signal is translated into visibility values (in meters) or into an extinction coefficient. These installations support weather reporting, airport operations, and safety decisions, providing continuous, automated visibility assessments.

Key design considerations include wavelength choice, alignment stability, calibration against standards, and environmental protection such as cleaning and temperature control. Strengths include continuous, non-contact measurements; limitations involve sensitivity to fouling, scattering, and misalignment, which can bias readings if not properly maintained.