The backscattering, or backward scattering, coefficient, in units of m^{-1}. It indicates the attenuation caused by scattering at angles from 90° to 180°. b_{b} is commonly estimated from measurements of the VSF around a single fixed angle. See Determining b_{b} with Fixed-Angle Sensors for details.
It is one of several coefficients derived from the Volume Scattering Function, each quantifying the total scattering within a particular range of angles. The most commonly seen is b, the total scattering coefficient. b_{f} is the forward-scattering equivalent of b_{b}, indicating scattering in the range of 0° to 90°.