Difference between albedo and emissivity?

Click For Summary
SUMMARY

The discussion clarifies the difference between albedo and emissivity, defining albedo as the ratio of radiation reflected off a surface to the total incident radiation, with black bodies having an albedo of 0 and reflective surfaces like snow having higher values, such as 0.9. Emissivity is not simply calculated as 1 minus albedo; rather, it represents the ratio of radiation emitted by a body compared to the total incident radiation. The confusion arises from the fact that emissivity values, such as 0.969 for snow, can exceed the albedo due to varying reflectivity and absorptivity across different wavelengths, particularly in the infrared spectrum.

PREREQUISITES
  • Understanding of albedo and emissivity concepts
  • Familiarity with thermal radiation principles
  • Knowledge of spectral reflectance and absorptance
  • Basic grasp of black body radiation theory
NEXT STEPS
  • Research the relationship between albedo and emissivity in different materials
  • Study the spectral properties of snow and its impact on thermal dynamics
  • Explore the concept of black body radiation and its applications
  • Learn about the effects of grain size on the reflectivity of snow
USEFUL FOR

Climate scientists, environmental researchers, and anyone studying thermal properties of materials, particularly in relation to snow and ice dynamics.

NatFex
Messages
26
Reaction score
3
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
 
Science news on Phys.org
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
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 18 ·
Replies
18
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 17 ·
Replies
17
Views
5K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 23 ·
Replies
23
Views
3K
  • · Replies 46 ·
2
Replies
46
Views
4K
  • · Replies 7 ·
Replies
7
Views
3K
Replies
8
Views
5K