Question

How many times, the electromagnetic energy passes through the atmosphere from the Sun to the Earth and back to the sensor?

• A. Three
• B. Two
• C. One
• D. Four

Hint:

In passive remote sensing the Sun is the energy source.

Answer 1

The Correct Option is B

Step 1: Set up the scene.
In passive remote sensing the Sun gives the light, the ground surface reflects it, and a sensor on a satellite records it.

Step 2: Trace the first journey.
Sunlight leaves the Sun and travels down through the atmosphere to reach the Earth's surface. That is one pass through the air.

Step 3: Trace the second journey.
The surface reflects part of that light upward. This reflected light travels back up through the atmosphere to reach the sensor. That is a second pass.

Step 4: Count the passes.
Down once, up once. So the energy crosses the atmosphere two times in total.

Step 5: Why this matters.
Both times the air can scatter or absorb some energy, which is why atmospheric correction is needed.

Step 6: Conclusion.
The electromagnetic energy passes through the atmosphere two times.
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