Optical Oceanographic Sensors

Optical Oceanographic Sensors measure the optical properties of water such as absorption, attenuation, scattering, fluorescence and volume scattering function. The instruments used to measure these parameters include:

Transmissometers are devices for measuring transmission or beam attenuation. They work by shining a narrow, collimated beam of light through the water. A receiver with a narrow field of view measures how much light arrives at the other end of a set distance. Light that is lost to absorption or is scattered will not be detected.

Nephelometers , or turbidity sensors, measure light scattering to determine the overall concentration of particles suspended in water.

Fluorometers provide an indication of the concentration of a given material by measuring the amount of fluorescence attributed to the material. For example, a fluorometer provides an excitation beam at a wavelength that is known to cause fluorescent emission from chlorophyll and measures light at a wavelength that matches the chlorophyll emission. As a result, the amount of chlorophyll-containing biomass can be estimated.

Spectrofluorometers are fluorometers that use multiple excitation wavelengths and multiple emission wavelengths to isolate and determine relative concentrations of different materials in the water.

Spectrophotomers measure the scattering of light. The volume scattering function (VSF) describes the directional dependence of this scattering. The VSF is an “inherent optical property” of water that is used by optical oceanographers to predict light propagation, image degradation, remote-sensed ocean color, biological environment, etc. in water. (long page from alpha-section)