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Re: [ATM] undercorrecting?
Re: [ATM] undercorrecting?Hi Stan,
You are right that there is quite a range in emissivity values.
I chose the Al-Cr-SiO one measured for the "GSFC Dark Mirror Coating". This (from the GSFC website) apparently is a high reflectivity layer used to define aperture on detectors. I expect that the SiO overcoat will influence the value...
Also, I can imagine that freshly deposited Al has a higher reflectance than a somewhat older coating.
Arjan
As in your link above, you use values related to "Polished Al", perhaps missing the Aluminum value in the Vapor Deposited Coatings segment of your citation. Very few mirror makers polish aluminum and use it as a reflector; rather, the bulk of our brethren use vapor deposited aluminum over glassy substrates. The value in the above link, gives a 0.02 emmisivity. I note that coating vendors routinely measure reflectances at or above 0.99 at 10 micron wavelengths for their aluminum films.
http://grus.berkeley.edu/~jrg/COATING/node3.html
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