Which sensor is not typically used to detect distance?

• A. Ultrasound
• B. Radar
• C. Thermal
• D. Laser

Answer: (C)

Measuring distance relies on how fast signals travel and how we interpret their return, or on geometric relationships between the sensor, object, and scene. A thermal sensor focuses on detecting infrared radiation to infer temperature, not the physical position or range of objects. Temperature readings don’t provide a reliable measure of how far away something is, so thermal devices aren’t used as distance sensors.

In contrast, ultrasound, radar, and laser sensors are all designed to gauge distance. Ultrasound sends sound waves and measures how long they take to bounce back, translating that time into distance. Radar emits radio waves and uses the same time-of-flight or phase methods for range, often with good performance in adverse conditions. Laser systems (LIDAR) send light pulses and measure their round-trip time (or use triangulation), delivering precise distance measurements with high resolution. Because of this direct capability to determine range, the thermal option is the best choice for not being used to detect distance.