How is ice a black body/almost a back body?

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Discussion Overview

The discussion centers around the properties of ice and snow as they relate to black body radiation, particularly focusing on how these materials can be considered nearly black bodies despite their visible appearance. The scope includes theoretical aspects of black body behavior and the specific wavelengths of light involved.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions how ice, which appears white and reflects most light, can be considered a black body or nearly so.
  • Another participant notes that snow is nearly perfectly absorptive in the infrared spectrum, suggesting that it behaves like a black body at near infrared wavelengths (1-3 microns).
  • A different participant emphasizes that while a black body theoretically appears black to the eye, it can behave like a black body within specific ranges of radiation, such as infrared, despite having an absorptivity and emissivity of 1 and reflectivity of 0 for all electromagnetic radiation.

Areas of Agreement / Disagreement

Participants express differing views on the characteristics of ice and snow as black bodies, with some agreeing on the infrared behavior while others highlight the apparent contradiction with visible light reflection. The discussion remains unresolved regarding the broader implications of these properties.

Contextual Notes

There are limitations in the discussion regarding the specific wavebands of interest, particularly in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) regions, which are not fully explored.

R Power
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I read somewhere that ice and snow are almost black bodies but the reason wasn't given.
But how can it be? Ice appears white...so it reflects most light incident on it, then how it can be even almost a black body? <:|
 
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Snow is (nearly) perfectly absorptive in the infrared.

http://www.civil.utah.edu/~cv5450/Remote/AVIRIS/optics.html

So at near infrared wavelengths (call it 1-3 microns) snow acts like a blackbody. Not sure about the MWIR (3-5 microns) and LWIR (8-12 microns) wavebands.
 
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thnx
 
You are right! A black body must, in theory, appear black to the eye. If the radiation of interest is limited to a particular range, say infrared, then the surface could be said to behave like a blackbody in this band. But strictly speaking, a blackbody has an absorptivity and emissivity of 1, and a reflectivity of 0 for all electromagnetic radiation.
 

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