Extract pixel radiance value from a raster

[PasqualeLanera]

Hello.

I have to make the water coloumn correction of some pleiades imagery with the Lyzenga method (1981).

So I have to select 6-7 omogeneus areas of sandy bottom (about 10 m2) and extract the radiance pixel value for the the three bands of these areas and calculate variance  and covariance.  WHich tool of ArcGIS10.3 could I use ?

Thanks