Explanation on band conversion from radiance to reflectance final value

Question

I've watched few video on conversion of radiance to reflectance for landsat band, most of them recommended to use formula below to to make sure the final reflectance value lies in between 0 to 1. My question is, is this method also categorized as method to NORMALIZE landsat image bands. Secondly, what value does the unknown represent?
Formula that I am referring to:
(B1 le 0)*0+(B1 ge 10000)*1+(B1 gt 0 and B1 lt 10000)*float (b1)/10000

your response/thoughts are very valuable to me.

Mikkel Lydholm Rasmussen · Answer

The formula that you are referring to does not convert from radiance to reflectance. As it currently is written, it simply fixes values above 1 and below 0. This type of formula is usually applied after a slightly incorrect atmospheric correction (such as flaash) has been applied, in an effort to remove unrealistic values.
The conversion of Landsat imagery from radiance to reflectance is usually done with the following x step approach:

Conversion from Digital Numbers to Radiance
Atmospheric Correction (using one of the many approaches for that)
(Optional) Fixing values below 0 or above 1 - this is what your formula does, assuming that the values have been scaled by 10000, which is normally only done to save a bit of disk space.

With the above in mind, if a proper atmospheric correction has been applied, then your imagery should be normalized. However, proper atmospheric correction does require some effort, as standard settings are likely not going to perform well.

Explanation on band conversion from radiance to reflectance final value

One Answer

Add your own answers!

Ask a Question