Active and Passive Sensors - Easy and Fast Explanation

What is an active sensor? What is a passive sensor?

A passive remote sensing sensor is one in which measures energy that is naturally available to it.

An example would be this camera that's filming me right now.
The red, green and blue spectral bands are naturally coming into the camera.

An active sensor, on the other hand, provides its own energy source for illumination.

For example, a radar satellite sends a signal down to the Earth's surface and waits for it to bounce back up to receive the signal back.
And the deformations in those signals allows it to generate an image. That is an active sensor.

Key Points
Key Point 1: Passive Remote Sensor: measures energy that is naturally available to it.
Key Point 2: Active Remote Sensor: provides its own energy source for illumination.

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