The Critical Difference

This sketch pictures the Weather Observation Tower at Kunsan Air Force Base, Korea as it appeared in 1971. Concrete bunkers, which occasionally sheltered fighter planes (F4 Phantoms, at the time), are seen in the background. At the base of the tower sits a Quonset hut which served as the Weather Equipment Maintenance Shop. The barrels mounted on stands outside remind me of an important cold weather responsibility: arrive early, open the oil valve and light the stove.

While the shop was warming up, we could stand around in our parkas or we could go up the tower and begin our preventive maintenance routines. It seems that I usually opted for the latter. Getting warm was always an incentive for going to work.

One piece of equipment we operated and maintained was a visibility set (called a Transmissometer). Actually, the Transmissometer’s measurements were quite limited. It only measured runway visibility or, more exactly, runway visual range. While this was of importance to pilots it wasn’t to forecasters. Nevertheless, the responsibility of providing this information to Air Traffic Control fell to the Weather Service.

The Transmissometer consisted of three major components. (Please bear with the details.) A transmitter and receiver, separated by approximately 150’, were positioned on platforms nearby and roughly parallel to the runway. The transmitter utilized a high intensity lamp that projected a light beam to a receiver. A photocell in the receiver turned the light into electrical energy and, after amplification, sent the current to the indicator in the tower. A current gauge (an amp meter) served to indicate visibility. Weather Observers referenced a chart which converted gage readings into distances. An upgrade to this system incorporated a Runway Visual Range Computer to do the conversion automatically, giving the Observer visibility measurements directly.

The downfall to all of this was the light beam. To insure that the lamp emitted a uniform amount of light, the transmitter utilized a constant voltage power supply. Unfortunately, lamp output was affected one other thing over which we had no control: physical deterioration of the filament. This made it necessary to confirm or correct the indicator’s reading on a daily basis. To do so, the Observer sighted landmarks of known distances and adjusted the indicator accordingly.

When the computer was first introduced, one Observer suggested that the ultimate goal was to make his job obsolete. Ironically, the computer’s accuracy depended on the Observers’ adjustments and so affirmed his importance.

Do people always make the critical difference? From what I have seen, they do. And, I suspect, they always will.

April 29, 2021

Michael Riley

More “Observations” to come . . .