A measure of the space rate of attenuation of any transmitted electromagnetic radiation. The attenuation coefficient is defined by
- dI = -aI0dx
- I = I0e-ax
where I is the flux density at the selected point in space; I0 is the flux density at the source; x is the distance from the source; and a is the attenuation coefficient.
- In general, the attenuation coefficient is specified only when the attenuation is known to be due to both absorption and scattering, or when it is impossible to determine which is the cause.