What is the difference between active and passive remote sensing?

Active and passive remote sensing represent two fundamentally different approaches to gathering information about the Earth's surface. The distinction hinges on how the sensors collect data.

Active remote sensing involves the use of sensors that emit their own energy, such as radar or LiDAR systems. These sensors send out signals, which then bounce back from the Earth's surface, allowing the sensors to measure how long it takes for the signal to return and in what form. This capability enables active sensors to collect data regardless of the natural light conditions, making them versatile for various applications, including night-time observations.

In contrast, passive remote sensing relies solely on detecting the natural energy that is reflected or emitted by surfaces, primarily sunlight. It utilizes energy from external sources, capturing this information through sensors aimed at recording visible light, infrared, or thermal energy. This method is dependent on daylight conditions and the visibility of natural light, which can limit its effectiveness in certain scenarios.

The correct answer reflects these essential characteristics: active sensing emits its own signals, while passive sensing detects energy that is naturally present. This distinction is crucial for understanding their respective applications in remote sensing and how they complement each other in gathering comprehensive geospatial data.