Part I Fundamentals

FUNDAMENTALS Part I of our book lays the physical and conceptual foundations of hydrologic optics, the quantitative study of the interactions of light with the earth's oceans, estuaries, lakes, rivers and other water bodies. Radiative transfer theory is the physical and mathematical framework for hydrologic optics. Chapter 1 begins with a few comments upon the nature of light itself and upon the sun, earth's primary source of light. We then briefly describe a few of the instruments used to quantitatively measure the flow of electromagnetic energy. Various concepts used in classifying electromagnetic energy are defined and discussed in some detail. These concepts – power, radiance, irradiance, and intensity – lie within the purview of geometrical radiometry and provide a complete set of building blocks for the mathematical structure of radiative transfer theory. Chapter 2 surveys the subject of photometry, the study of how radiant energy is perceived by the human eye and brain. Strictly speaking, this material is extraneous to the study of radiative transfer. 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. In Chapters 1 and 2 we learn how to measure and describe light; in Chapter 3 we learn how to specify the optical properties of the medium through which the light propagates. Inherent and apparent optical properties are defined, and we review the current literature on values and bio-optical models for the absorption, scattering, and attenuation properties of natural waters.