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Ocean Optics Web Book

Light and Radiometry


Page updated: Apr 11, 2017
Principal author: Curtis Mobley

This chapter lays the physical and conceptual foundations of optical oceanography, or more generally of hydrologic optics, the quantitative study of the interactions of light with the earth's oceans, lakes, rivers and other water bodies. The Level 1 material starts with an overview of light and the basics of light detectors. We then show how to specify directions and other geometrical concepts such as solid angle in a manner suited to the mathematics of radiative transfer theory. We finally define various quantities such as radiance and irradiance, which provide the building blocks for discussions of the absorbing and scattering properties of water and for the mathematical structure of radiative transfer theory, which are the topics of later chapters.

After defining the basic terms, there are Level 2 discussions of blackbody radiation, light from the sun, and comments on various details of the Level 1 material.

Much (but not all) of the work done in optical oceanography can be done without consideration of the state of polarization of the light. Polarization is therefore discussed in Level 2.

There is a Level 2 survey of photometry, the study of how radiant energy is perceived by the human eye and brain. Strictly speaking, photometry is extraneous to optical oceanography and radiative transfer theory. Yet it is photometry, not the physical science of radiometry, that enables us to understand the connections between radiant energy and subjective concepts such as brightness and color.

The design and calibration of radiometric instruments are discussed in Level 3, which also contains links to commercial instrument manufacturers.

Most of this Chapter 2 material is reformatted and revised from the 1994 text Light and Water (1994), which you can download in its entirety.

Figure [*] shows the "learning path" for this chapter. The linear path through the sections of Level 1 material shows the order needed to understand the material, assuming no previous knowledge. The Level 2 material can be understood after completing the Level 1 section that connects to a topic in Level 2. Each level 2 or 3 section is self-contained.

Figure: The learning path through Chapter 2.
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