Electromagnetic Spectrum and Atmospheric Windows MCQ with answer and solution

Concept

Remote sensing sensors are classified as active or passive based on their source of energy.

Step-by-step solution

1. Understand that remote sensing means getting information about an object from a distance using sensors. 2. A 'Passive Sensor' does not have its own light or energy source. It waits for natural energy to reflect off the Earth's surface. 3. The most common natural source of energy for passive sensors during the day is the sun. 4. The sensor detects the solar radiation (sunlight) that bounces back from objects like trees, buildings, or water. 5. Active sensors, on the other hand, use their own energy (like a flash or radar pulse). Answer: (A) sun as the source of energy

Explanation

Passive sensors detect natural radiation that is emitted or reflected by the object. The sun is the primary source of this external energy for most passive remote sensing systems. These sensors cannot work at night unless they detect thermal heat emitted by the Earth.

Why the other options are wrong

B: The moon's light is too weak for standard passive remote sensing compared to the sun. C: A flash light is an artificial source; if a sensor uses it, it becomes an active sensor. D: This is the definition of an 'Active Sensor', not a passive one.

Shortcut

Passive = Uses natural energy (Sun). Active = Uses its own energy (Radar/Laser).

Common mistake

Students often confuse passive sensors with active ones, thinking the sensor always provides the light.