Difference between albedo and emissivity?

  • #1
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Main Question or Discussion Point

This has been asked already, but it was either answered incorrectly or I'm just not understanding it right.

I was under the impression that albedo is the ratio of radiation reflected off a body compared to the total incident on that body. Hence black bodies have an albedo of 0 and more white/shiny surfaces have higher albedos.

I thought emissivity = 1-albedo, so, the ratio of radiation absorbed (and therefore emitted) compared to the total incident radiation, because radiation is either reflected or absorbed then emitted, right?

So, according to values on the internet, snow has an albedo of 0.9 (Wikipedia) and an emissivity of 0.969+ (EngineeringToolbox). How does that make sense? How can the radiation emitted and absorbed add up to more radiation than there was in the first place?

Thanks
 

Answers and Replies

  • #2
Andy Resnick
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The references are unclear about the specified wavelength range. For example, snow is highly reflective in the visible but highly absorptive in the infrared. In addition, the reflectivity for snow can be highly variable based on grain size. Basically, the two numbers may not be directly comparable:

http://nsidc.org/data/docs/daac/nsidc0066_avhrr_5km/spectra.jpg
 

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