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20000210: Brightness vs reflectance in NOAA/AVHRR visual bands

------- Forwarded Message

>From: "Panagiotis Elias" <address@hidden>
>Organization: EOS Greece
>Keywords: 200002101232.FAA08532 McIDAS NOAA AVHRR reflectance brightness

> Hi all,
> Do you know how the brightness value related to reflectance  in NOAA/AVHRR
> visual bands (1&2)?
> Thank you!
> Panagiotis D. Elias
> National Observatory of Athens
> Institute for Space Applications and Remote sensing

     Yes.  If R is the reflectance in percent, then DN = 25.5*sqrt(R)

     So that if R=100 percent, the digital brightness will be 255.
The square root representation allows more contrast at low levels so
it is easier to see ground features.  Of course it means less resolution
at the cloud tops.


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