The attenuation (loss of light) of a narrow, well collimated beam of light is due to both absorption and scattering. When referenced to pure water, the beam attenuation coefficient describes light losses due to absorption by dissolved materials and particulates and due to scattering by particulates.
In the red part of the spectrum, attenuation due to dissolved materials is negligible, so that attenuation in the red is due primarily to particles. Light that is absorbed cannot be scattered, so that to first order the absorption and scattering processes compensate each other. The beam attenuation coefficient in the red is an excellent proxy for the total volume of particles.
The beam attenuation coefficient at 650 nm depends on the nature of the particles, or their size, shape and internal index of refraction distribution.The beam attenuation coefficient at 532nm has been shown to be strongly negatively correlated with the visibility of a 200mm diameter black target. This is the visibility parameter.
Sensors
C-Star transmissometer:
measures the beam transmission (underwater visibility parameter) at 532 nm
measures total suspended particle mass at 650 nm
ac-s, ac-9 underwater spectrophotometers:
measure the attenuation spectrum
More about...
Intro to IOPs
More on IOPs: absorption • beam attenuation • volume scattering function • fluorescence • turbidity • scattering
Mail to: PO Box 518 • Ship to: 620 Applegate St. • Philomath, OR 97370 • 541-929-5650 • Fax: 541-929-5277 • wetlabs@wetlabs.com
