Which statement best describes passive ranging?

• A. Passive ranging uses track gates to determine distance based on target size
• B. Passive ranging uses the LRF to measure distance
• C. Passive ranging relies on GPS data
• D. Passive ranging uses radar to estimate distance

Answer: (A)

Passive ranging estimates distance to a target by using cues from the target itself, without emitting signals. In a passive seeker, the system keeps the target within track gates, a window that follows the target as it moves. By measuring how large the target appears in the sensor image and knowing the target’s real size, the distance can be calculated. The basic idea is simple: if the target looks bigger, it’s closer; if it looks smaller, it’s farther away. This relies on angular size and known dimensions, so the range comes from geometry rather than an emitted ranging signal. This approach is distinct from methods that actively send out a signal, like laser rangefinding or radar, or from using external data such as GPS.