ISO/TC 211 Multi-Lingual Glossary of Terms (MLGT)

Note 1 to entry: Radar cross section is calculated as ${\displaystyle \sigma =\underset{R\to \infty }{lim}4\pi R^2\frac{{\left|E_s\right|}^2}{{\left|E_i\right|}^2}}$ where ${\displaystyle \sigma }$ is the radar cross section; ${\displaystyle E_i}$ is the electric-field strength of the incident wave; ${\displaystyle E_s}$ is the electric-field strength of the scattered wave at the radar with a distance ${\displaystyle R}$ away from the target.

Note 2 to entry:  2 to entry: Radar cross section has the dimensions of area, with the unit of square metres. Usually, it is expressed in the form of a logarithm with the unit of dBsm as follows ${\displaystyle {\sigma }_{\text{dBsm}}=10{\log }_{10}^{}\sigma }$