What does the transmissometer look like?

• A. A single long tube with sensors
• B. A small radar dish
• C. Four telescopes arranged in a circle
• D. Looks like 4 telescopes looking at each other

Answer: (D)

Transmissometers are used to measure how far you can see along a runway by sending a light beam along a defined path to a receiver. Visually, the important clue is that you’re dealing with optics that face each other across a straight light path—essentially two sets of transmitter/receiver optics. Describing the device as looking like four telescopes looking at each other captures that arrangement: you can picture four small optical heads arranged so two are sending the beam and two are receiving it, all aimed across the path toward the opposite side. The other descriptions don’t fit this setup: a single long tube with sensors isn’t the typical stark optical heads facing across a path; a small radar dish points to radar equipment, not an optical transmissometer; four telescopes in a circle don’t portray the opposite-facing beam alignment needed to measure transmitted light.