What is the term used for remote sensing that actively emits a signal or energy and measures the return?

• A. Passive Remote Sensing
• B. Synchronous Remote Sensing
• C. Active Remote Sensing
• D. Reflective Remote Sensing

Answer: (C)

Active remote sensing refers to a method where an instrument emits its own signal or energy, such as radar or lidar, and then measures the energy that is reflected back from the target. This process allows for the collection of detailed information about the target's characteristics, such as distance, shape, and material properties.

In contrast, passive remote sensing relies on natural energy, typically sunlight, which is reflected or emitted by the Earth's surface. This means it does not generate its own signal but instead captures the already present energy.

Synchronous remote sensing is not typically a standard term used in the context of remote sensing techniques and does not specifically describe any of the methods associated with signal emission or measurement.

Reflective remote sensing does not accurately capture the essence of what active remote sensing entails, as it implies a focus only on returning signals without the aspect of active emission.

Overall, active remote sensing is crucial for applications requiring precise measurements under various conditions and is essential in various fields such as environmental monitoring, agriculture, and urban planning.