Passive Remote sensing

So far, we have read various definitions and descriptions of Remote Sensing. But only an appropriate definition would make the very concept of Remote Sensing clear. Remote Sensing is the acquisition of information about an object or phenomenon relating to the object without making any kind of physical contact with the object.

Passive Remote sensing

Passive remote sensing is a class of Remote Sensing that make use of Passive Remote Sensors. The sensors are used to detect natural radiations that are emitted by the object or by its surrounding areas. The most common source of energy that is measured by Passive Remote Sensors is “Reflected Sunlight”.

The sensors that are used for Passive Remote Sensing can only be used when there is some naturally occurring energy available. Thus, for all reflected energy, Passive Remote Sensing can only take place when the sun is illuminating the surface of the earth. No reflected is available from the sun at night.

Passive Remote Sensors obtain measurements from naturally occurring radiations. The sensors have several characteristics and they are often called its advantages :

• Multiple wavelength information

• Comparatively low electrical power requirements

• Small size possible

The Passive Remote Sensing systems are pretty much similar to what the eyes see. They are more or less similar to photographs. Passive Sensing radiates visible light. Some of the very common examples of Passive Remote Sensing are :

• Charge-Coupled Devices

• Infrared

• Film Photography

• Radiometers

The energy that is radiated naturally can be detected day or night, as long as the amount of energy is large enough to be recorded.