Discuss Principles of active RS system and its advantages over Passive system.
Answers
Active sensors have its own source of light or illumination. In particular, it actively sends a wave and measures that backscatter reflected back to it.
But passive sensors measure reflected sunlight emitted from the sun. When the sun shines, passive sensors measure this energy. But more on this later.
Cameras are passive AND active sensors
When you take picture with the camera flash turned on, what’s exactly happening here?
The camera sends its own source of light to the target and reflects back to the camera lens. This is the light that your camera captures.
Active Remote Sensing Camera Example
Active Remote Sensing Camera Example
You can think of active remote sensing like a handheld camera with the flash turned on. But active remote sensing can be space-borne satellites orbiting the Earth or airborne on an aerial unit.
Cameras are active sensors when the photographer uses flash. It illuminates its target and measures the reflecting energy back to the camera.
Cameras are passive sensors when the photographer does not use the flash. Because the camera is not sending the source of light, it uses naturally emitted light from the sun.
passive remote sensing camera example
Passive remote sensing camera example
As you’re about to find out, there are hundreds of applications for passive and active remote sensing. But first, let’s dig a bit deeper in both types of remote sensing.
Examples of passive and active remote sensing
Now that we have a clear understanding of passive and active remote sensing, let’s see it in action for satellite sensors. In the schematic below, you can see how the sun emits light. For the light that passes through the atmospheric window, it reflects off Earth to a satellite sensor orbiting Earth.