Question

Which of the followings is an active sensor?

• A. Multispectral scanner
• B. Hypersepctral scanner
• C. Thermal scanner
• D. Laser scanner

Hint:

Active sensors like LiDAR and RADAR are "all-weather" and "all-time" sensors, unlike passive sensors which mostly require sunlight.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
In remote sensing, sensors are classified into two categories:
1. Passive Sensors: They detect natural radiation (usually sunlight) reflected or emitted from the Earth's surface.
2. Active Sensors: They provide their own source of energy (EM radiation) and detect the portion of that energy that is reflected or backscattered from the target.

Step 2: Detailed Explanation:
Multispectral (Statement 1) and Hyperspectral (Statement 2) scanners are passive. They rely on the sun's illumination to detect energy across various bands.
Thermal (Statement 3) scanners are also passive as they detect heat (longwave radiation) naturally emitted by objects.
A Laser scanner (Statement 4), commonly known as LiDAR (Light Detection and Ranging), is an active sensor.
It emits laser pulses (usually in the infrared range) towards the target and measures the time it takes for the pulse to return.
Because it provides its own illumination, it can be used day or night and can penetrate forest canopies to map the terrain underneath.
Other examples of active sensors include RADAR and Sonar.

Step 3: Final Answer:
The Laser scanner is an active sensor because it emits its own electromagnetic pulses.