Hi Jerson,

There are a couple ways of doing this.

You can use Focus > Analysis > Overlay > Statistical. The primary input layer is the polygon layer; the secondary layer is the raster channel. You would need to compute the Std Dev and Mean separately, then use Field > Compute in the Attribute Manager to compute the coefficient of variation (Std Dev / Mean).

You could also use VIMAGE to compute the Std Dev and Mean.

 Another formula for CV (as a percentage):

Coefficient of Variation = (Standard Deviation / Mean) * 100

 Hope this helps!