...the transfer of radiant energy in ocean waters and the effects of energy absorption on biological productivity. 

Optical oceanography is ecologically important because...

...water both absorbs and scatters radiant energy, both the intensity and the spectral quality of radiation vary markedly with depth. This means that in all but the shallowest waters, light availability is a limiting factor in primary production. To achieve a high rate of primary production, an aquatic plant community -- the phytoplankton and macrophytes -- must absorb a high rate of light energy by its photosynthetic system and convert the photosynthate to new cell material.

...the wavelength band between 400 nm and 700 nm, which is the wavelength interval where chlorophyll can absorb and utilize photons of near ultraviolet and visible wavelengths; sometimes only the 400 nm to 700 nm wavelength interval is used since at wavelengths shorter than 400 nm the near-ultraviolet photons are rapidly absorbed near the water surface except in very clear waters. The 400-700 nm wavelength interval is the typical range of wavelengths for human vision under bright lights and is at the peak of the energy spectrum from the sun, which is why the word "light" often replaces the word "energy" when describing the energy transfer in water.

The "photosynthetically available radiation", PAR, (photons s^-1 m^-2) in that wavelength interval is the number of photons available for photosynthesis. Bio-optical literature often states PAR in different units, einst s^-1 m^-2 or einst s^-1 m^-2. One einstein is one mole of photons (6.02 x 10²³ photons).

Optical oceanography also is important...

...for some military applications.

...the absorption and scattering properties of the water (which influence the amount of light available for primary production) depend on the phytoplankton and macrophytes in the water. That is, there is a feedback effect. The coupling of the physics of radiative transfer (of primary interest to theoretically inclined oceanographers and physicists) and the biological effects of energy absorption (of primary interest to biological oceanographers) means that ocean optics is truly interdisciplinary. The presence of zooplankton further complicates the analysis if one attempts to account for all the effects on the transfer of radiation in water. For this reason absorption and scattering properties sometimes are separated into separate contributions from pure water, chlorophyll, colored dissolved organic matter (CDOM), etc.

Radiative transfer analysis for water is also complicated by the fact that pure water optical properties, as well as those of the biological constituents, are spectrally-dependent. In addition, the scattering greatly complicates the analysis since photons can change direction in a scattering event, and the culmination of many scattering events tends to broaden even a narrowly-collimated beam of light (e.g., from a laser).

Ocean waters are broadly categorized as...

...Case 1 waters if the absorption and scattering properties can be correlated with chlorophyll concentration, and Case 2 waters (nearly all coastal waters) if such correlations cannot be inferred or do not exist.

...the inherent optical properties (IOPs), which are the absorption and scattering coefficients that depend only on the constituents of the water, as described above, and the apparent optical properties (AOPs) that depend on the surface illumination as well as the IOPs. Since it is the IOPs that affect primary production and it is the AOPs that are measured with radiation instrumentation, one must develop procedures with which to infer the IOPs from the AOPs. Such procedures are related to the solution of "inverse problems" of radiative transfer. Different procedures typically are developed for different optical instruments.

The AOPs of most interest are...

...a) the spectral radiance (W m^-2 sr^-1 nm^-1), i.e., the power that crosses a unit area at a given depth and in a particular direction and wavelength interval, which is measured with a narrow field-of-view detector, and/or

b) the downward and upward spectral planar (or "vector") irradiances (W m^-2 nm^-1), i.e., the power that crosses a unit area at a given depth in a particular wavelength interval, which is measured with a "cosine" (or "flat-plate") detector.

Measurements made out of the water (i.e., "remotely") can be used to infer the ocean color, which gives information about the IOPs near the surface, or measurements made in the water (i.e., "in situ") at different depths can be used to determine IOPs as a function of depth. For some in situ measurements an externally-generated light source is used to create the local light field, in which case the inversion algorithm is for an "active" sensing application, but if only the inherent, naturally-occurring light from solar radiation is measured, then the inversion algorithm is for a "passive" sensing application.

An AOP of interest for primary production is...

...the spectral scalar irradiance (W m^-2 nm^-1), which has the same units as a spectral irradiance, but unfortunately is much more difficult to measure because "2 pi" radiation detectors are needed. So the inference of the scalar irradiance from other radiation measurements is another important radiative transfer problem in the discipline of optical oceanography.

...because in a forward problem one typically specifies the IOPs everywhere as a function of depth, along with the surface illumination and the bottom "albedo" boundary conditions, and seeks to determine the radiant energy transported through the water. On the other hand, in an inverse problem one typically knows the amount of radiant energy (from measurements of the AOPs) and seeks to determine, for example, the IOPs. Other inverse problems of interest are the determination of the amount of fluorescence or bioluminescence in the water. The procedure or method by which an inverse problem is solved is sometimes referred to as an "algorithm".

References for optical oceanography are...

Monographs:

J. T. O. Kirk, 1994: Light and Photosynthesis in Aquatic Ecosystems, 2nd ed. (Cambridge) (This is certainly the best book for people more interested in the biological aspects of radiative transfer.)

C. D. Mobley, 1994: Light and Water, Radiative Transfer in Natural Waters (Academic) (This is a book that gives the details of how radiative transfer calculations can be done, as well as a physicist's approach to biological oceanography.)

R. W. Spinrad, K. L. Carder, and M. J. Perry, 1994: Ocean Optics (Oxford) (This is a compendium of some review articles, some of which are very well written.)

R. E. Walker, 1994: Marine Light Field Statistics (Wiley) (This has an introduction to atmospheric and oceanic optics and an extensive coverage of sea-surface and refracted light statistics.)

R. P. Bukata, J. H. Jerome, K. Ya. Kondratyev, and D. V. Pozdnyakov, 1995: Optical Properties and Remote Sensing of Inland and Coastal Waters (CRC Press) (As the title implies, this gives details about inherent optical properties.)

G. E. Thomas and K. Stamnes, 1999: Radiative Transfer in the Atmosphere and Ocean (Cambridge) (This gives an excellent introduction to the computational aspects for both atmospheric and oceanic applications.)

K. Ya. Kondratyev and N. N. Filatov, 1999: Limnology and Remote Sensing A Contemporary Approach (Springer-Praxis) (The coverage on optical remote sensing is applicable to any body of water.) 

A. A. Kokhanovsky, 2001: Optics of Light Scattering Media Problems and Solutions, 2nd ed. (Springer-Praxis) (This includes a comprehensive introduction to the electromagnetic theory of single scattering and to radiative transfer.)

K. S. Shifrin, 1988: Physical Optics of Ocean Water (American Institute of Physics) (This is the translation from Russian of a 1983 text.)

H. R. Gordon and A. Y. Morel, 1983: Remote Assessment of Ocean Color for Interpretation of Satellite Visible Imagery, A Review (Springer-Verlag) (This is an older text devoted primarily to remote sensing and includes a discussion of the differences between Case 1 and Case 2 waters.)

Other Major References:

Ocean Optics VIII, IX, X, XI, XII, XIII, Society of Photo-Instrumentation Engineers conference proceedings:

VIII, SPIE Vol. 637, is from the 1986 Orlando meeting,
IX, SPIE Vol. 925, is from the 1988 Orlando meeting,
X, SPIE Vol. 1302, is from the 1990 Orlando meeting,
XI, SPIE Vol. 1750, is from the 1992 San Diego meeting,
XII, SPIE Vol. 2258, is from the 1994 Bergen (Norway) meeting,
XIII, SPIE Vol. 2963, is from the 1996 Halifax (Nova Scotia) meeting.

Contact the U. S. Office of Naval Research for CDs of the Ocean Optics meetings every two years beginning in 1998.

Limnology and Oceanography, Vol. 34, No. 8: the December 1989 special issue on Hydrologic Optics

Journal of Geophysical Research, Vol. 100, No. C7: the July 15, 1995 special issue on Advances in Ocean Optics: Issues of Closure