Beam attenuation coefficient c: is described as attenuation of parallel formed light along a path r by processes of scattering and absorbtion of radiant energy in environment. Operational definition

c(l)=-1/r ln{L_r(l)/L₀(l)}

where L_r, L₀ are subsequently radiance after travelling path r and source radiance; (l) denotes dependence on light wavelength.

• parameter symbol: c
• units of measure: m^-1
• range: 0.4 - 5.0 m^-1