The use of a radiometer to quantitatively describe the power from a specific light field. The description can be made in terms of several properties including magnitude, geometrical distribution (or direction), spectral distribution, state of polarization, and time variability. Before the advent of satellite oceanography, the primary use of radiometry was to sample the radiant power in the vicinity of an organism to obtain quantitative information about how it reacts to light. Now the use of radiometers in instruments aboard satellites to measure various properties of incident, reflected and emitted radiation is nearly ubiquitous, with new types of radiometers seemingly developed for each new mission.