In a transmissometer, a beam of visible light is transmitted from its transmitter to receiver head.

There also are sensors that, to a certain degree combine a transmissometer with a forward scatter sensor.

A transmissometer is an instrument for measuring the extinction coefficient of the atmosphere, and for the determination of visual range.

The term transmissometer is also used by oceanographers and limnologists to refer to a device for measuring the optical properties of natural water.

As a complex system, VPR can also carry several oceanographic sensors in the same time such as, CTD, transmissometer, fluorometer and flowmeter.

Latest generation transmissometer technology makes use of a co-located forward scatter visibility sensor on the transmitter unit to allow for higher accuracies over an Extended Meteorological Optical Range or EMOR.

According to the US Federal Aviation Administration: "There are approximately 279 RVR systems in the NAS, of which 242 are forward scatter NG RVR Systems and 34 are older Transmissometer Systems."