Are pixel intensities proportional to radar cross section in sar images?

This paper discussed the problems associated with denoting RCS as the radiometric measurement quantity in SAR images. The root cause was identified to be the principal frequency dependence of the target backscatter. It was proposed to replace RCS by equivalent RCS as the radiometric measurement quantity in SAR images because a SAR system does not measure RCS and therefore another terminology should be used to describe the measurement quantity.