How does DME interrogation determine slant range distance?

Determining slant range distance through DME (Distance Measuring Equipment) interrogation primarily relies on the calculation of the time delay of the interrogation signal. In this process, an aircraft transmits a signal to the DME ground station, which then responds with a signal of its own. The aircraft's onboard equipment calculates the time it takes for the signal to travel to the station and back.

Since radio waves travel at the speed of light, the time delay is used to calculate the distance to the ground station. Specifically, the slant range is derived from the round-trip time, which provides an accurate measurement of the distance based on that time. This technique ensures that pilots and navigators can pinpoint their position relative to the DME station effectively.

Other methods such as measuring signal strength, triangulating multiple signals, or using GPS coordinates are not directly involved in the same manner as time delay calculations in determining slant range, which makes the measurement of time delay the correct approach in this context.