Effective noise temperature of Earth as seen from space What is the approximate average noise temperature of the Earth when observed from space in the microwave region (clear-sky, broad view)?

Introduction / Context:
Effective noise temperature describes the equivalent blackbody temperature that would produce the observed radiometric emission. For Earth as viewed from space, this value is close to its effective radiating temperature used in climate models.

Given Data / Assumptions:

• Earth’s effective radiating temperature ≈ 255 K.
• Microwave observations integrate land, ocean, and cloud cover.

Concept / Approach:
Radiative balance and radiometry establish that the Earth emits like a ~255 K blackbody on average. Satellite system noise calculations often use a similar figure for Earth-viewed background temperature.

Step-by-Step Solution:
Recall T_effective ≈ 255 K from planetary energy balance.Choose the closest option: 254 K.

Verification / Alternative check:
Remote sensing references routinely cite 250–260 K as the typical range for effective Earth radiative temperature.

Why Other Options Are Wrong:
303 K corresponds to warm surface temperatures; 100 K and 500 K are far from Earth’s mean radiative properties.

Common Pitfalls:
Confusing surface temperature with effective radiative temperature; they are not identical.

Final Answer:
254 K