Active and Passive Sensor Types
Remote sensing is the process of gathering information about objects or areas from a distance, typically using satellites or aircraft. It plays a crucial role in observing Earth and other planetary bodies, enabling scientists to collect data on a global scale. Remote sensing instruments detect and record energy reflected or emitted by the Earth's surface, allowing for data-informed decision making about our planet's systems. One key distinction in remote sensing is between active and passive sensor types. Passive sensors detect natural energy, such as sunlight reflected from the Earth's surface, while active sensors emit their own energy and measure the return signal. Understanding these sensor types is essential for interpreting remote sensing data and applying it to various scientific and practical applications.
Figure (1)
They rely on existing light or radiation already present in the environment. Active sensors, on the other hand, emit their own energy, such as radar or laser pulses, and then measure the energy that bounces back. This lets them work in all weather and at night, since they don’t depend on sunlight.
The key difference is that passive sensors only observe what is already there, while active sensors create their own signal to send out. For example, a camera on a satellite is a passive sensor because it captures sunlight reflecting off Earth. Radar on a satellite is an active sensor because it sends out radio waves and records what returns.
Students should picture passive sensors like a camera taking a photo of a scene lit by the sun. Both types help scientists understand Earth's surface and atmosphere in different ways.
Key Points
- Active sensors emit energy to scan objects and measure the radiation that is reflected or backscattered from the target.
- Passive sensors gather radiation that is emitted or reflected by the object or surrounding areas.
- Radar is a type of active remote sensing which uses electromagnetic energy backscattered from ground targets to extract physical and dielectric behavior.
- Lidar is used for weapon ranging, laser illuminated homing of projectiles, and to detect and measure the concentration of various chemicals in the atmosphere while airborne lidar can be used to measure the heights of objects and features on the ground more accurately than radar technology.
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Sources & licensing(4)
- NASA Earthdata — www.earthdata.nasa.gov/learn/earth-observation-data-basics (U.S. Government work (public domain, 17 U.S.C. 105))
- Wikipedia contributors — en.wikipedia.org/wiki/Remote_sensing (Creative Commons Attribution-ShareAlike 4.0)
- Wikipedia contributors — en.wikipedia.org/wiki/Radar_remote_sensing (Creative Commons Attribution-ShareAlike 4.0)
- Wikipedia contributors — en.wikipedia.org/wiki/Wave_radar (Creative Commons Attribution-ShareAlike 4.0)