How is Runway Visual Range (RVR) typically measured?

Runway Visual Range (RVR) is specifically measured using instruments known as transmissometers. These devices determine the distance a pilot can see down the runway by measuring the amount of light that is transmitted through the atmosphere and received at the other end. They are designed to provide accurate and consistent readings in various weather conditions, including fog, rain, or snow, thus offering essential information for safe aircraft operations.

Transmissometers work by emitting a light beam across the runway and measuring how much of that light is scattered by particles in the air, such as moisture or dust. The data obtained allows for the calculation of the effective visual range, which is critical for making informed decisions regarding takeoffs and landings.

Other methods, such as using portable visibility measuring tools or relying on pilot reports, may provide additional context or supplemental information regarding visibility conditions, but they do not offer the systematic and precise measurements that transmissometers do. Similarly, a simple visibility chart is not capable of providing the specific RVR readings necessary for runway operations. Thus, transmissometers are the key instruments for measuring RVR accurately.