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leaf emissivity
11-18-2012, 11:49 PM
Post: #1
leaf emissivity
Hi, does anyone know how to get the leaf emissivity? I read Fuchs 1966 paper about using a cone with aluminium foil inside. if put the cone on the leaf, it will give an leaf emissivity of 1.0, then remove the cone, it will give total energy emitted by leaf and also the reflected energy by the background. So, If I want to get the background temperature using aluminum foil plate, shall I use the shining side or the dark side of the aluminum foil? I see that people suggest to use the shining side, but why? I tried in my field with wrinkled aluminum foil and place it under the sun, in some spots it showed very high temperature through the camera. Does the hot spot show the specular reflection? How can I distinguish diffused and specular reflection? Can I use the dark side of the aluminum foil to get diffused reflection and shining side to get specular reflection? Am I right in this point?
Thanks very much.
Rose
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11-20-2012, 12:30 PM (This post was last modified: 11-20-2012 12:31 PM by Gary Orlove.)
Post: #2
ITC RE: leaf emissivity

  1. Put a dab of Liquid Paper on the leaf as an emissivity reference at 0.95.
  2. Reflected apparent temperature can be determined with shiny or dull side of foil, makes no difference to an IR camera.
  3. I would make the measurement on a cloudy day or clear night to avoid solar reflection effects.
  4. Remember that to make an emissivity measurement, the object (leaf) MUST BE at a temperature that is different than the reflected apparent temperature, the larger the difference, the more accurate the measurement.
See http://irinformir.blogspot.com/2012/02/thermographic-measurement-techniques.html
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11-23-2012, 02:54 PM
Post: #3
RE: leaf emissivity
(11-18-2012 11:49 PM)rosedeng Wrote:  Hi, does anyone know how to get the leaf emissivity? I read Fuchs 1966 paper about using a cone with aluminium foil inside. if put the cone on the leaf, it will give an leaf emissivity of 1.0, then remove the cone, it will give total energy emitted by leaf and also the reflected energy by the background. So, If I want to get the background temperature using aluminum foil plate, shall I use the shining side or the dark side of the aluminum foil? I see that people suggest to use the shining side, but why? I tried in my field with wrinkled aluminum foil and place it under the sun, in some spots it showed very high temperature through the camera. Does the hot spot show the specular reflection? How can I distinguish diffused and specular reflection? Can I use the dark side of the aluminum foil to get diffused reflection and shining side to get specular reflection? Am I right in this point?
Thanks very much.
Rose



I would suggest measuring the reflectivity, and then calculating the emissivity by 1-R.

Also as an alternative to heating the leaf, place it in a cold environment so as it is a a different temp to the Trefl.
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12-07-2012, 08:17 AM
Post: #4
RE: leaf emissivity
Hi GaryThanks very much for your reply. I've tried the foil method you mentioned in the link, but find the temperature range of the foil is very large and hard to determine what temperature to use as background temperature. please see images i took in a night. here is the link
http://dl.dropbox.com/u/108800495/foil%20temperature.png
ThanksRosenotes on the images were taken under a bit windy night, but images were taken when it's stable. the images were crumbled aluminum foil on a paper plate. the high temperature line is transparent tapes (to fasten the foil to plate). The upper corner of lower right image are smooth foil that are not crumbled for comparison.It can be seen that the temperature range of foil is very large.[/font]
(11-20-2012 12:30 PM)Gary Orlove Wrote:  
  1. Put a dab of Liquid Paper on the leaf as an emissivity reference at 0.95.
  2. Reflected apparent temperature can be determined with shiny or dull side of foil, makes no difference to an IR camera.
  3. I would make the measurement on a cloudy day or clear night to avoid solar reflection effects.
  4. Remember that to make an emissivity measurement, the object (leaf) MUST BE at a temperature that is different than the reflected apparent temperature, the larger the difference, the more accurate the measurement.
See http://irinformir.blogspot.com/2012/02/thermographic-measurement-techniques.html
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12-07-2012, 10:34 AM
Post: #5
RE: leaf emissivity
You are correct, the temperature variation on the foil can be large because in the real world, few materials are super specular reflectors, in nature, diffuse reflectors are more the norm. That's why we crumple the foil, to better simulate a diffuse reflector. Use the average temperature in the region of interest as your reflected apparent temperature.
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12-09-2012, 08:42 PM
Post: #6
RE: leaf emissivity
Thanks very much for the prompt reply. It makes me more confident to use the data.CheersRose

(12-07-2012 10:34 AM)Gary Orlove Wrote:  You are correct, the temperature variation on the foil can be large because in the real world, few materials are super specular reflectors, in nature, diffuse reflectors are more the norm. That's why we crumple the foil, to better simulate a diffuse reflector. Use the average temperature in the region of interest as your reflected apparent temperature.
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03-19-2013, 11:57 AM
Post: #7
RE: leaf emissivity
Hi i'm kind of studying the same topic here but my subject is palm oil, i'm interested to study the using the emissivity value proving presence of oil or present of water (moisture) in palm oil. Any one can suggest the best way to do it.
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