Spectrum generation from single SAR imagery

I have created the RGB from the Sentinel-1 imagery. I am trying to generate the spectrum from the RGB composite of the imagery.

Is it possible to generate the spectrum from intensity/backscatter vs (VV, VH, (VH-VV))?

Kindly help me to resolve the issue.

You can assign a wavelength to a band if it is different from zero the band will be shown in the spectrum view.
Right-click on the band and select ‘Properties’. There you can set the wavelength.

Thank you so much.