Book contents
- Frontmatter
- Contents
- Preface to the first edition
- Preface to the second edition
- Part I The underwater light field
- 1 Concepts of hydrologic optics
- 2 Incident solar radiation
- 3 Absorption of light within the aquatic medium
- 4 Scattering of light within the aquatic medium
- 5 Characterizing the underwater light field
- 6 The nature of the underwater light field
- 7 Remote sensing of the aquatic environment
- Part II Photosynthesis in the aquatic environment
- References and author index
- Index to symbols
- Index to organisms
- Index to water bodies
- Subject index
5 - Characterizing the underwater light field
Published online by Cambridge University Press: 25 January 2010
- Frontmatter
- Contents
- Preface to the first edition
- Preface to the second edition
- Part I The underwater light field
- 1 Concepts of hydrologic optics
- 2 Incident solar radiation
- 3 Absorption of light within the aquatic medium
- 4 Scattering of light within the aquatic medium
- 5 Characterizing the underwater light field
- 6 The nature of the underwater light field
- 7 Remote sensing of the aquatic environment
- Part II Photosynthesis in the aquatic environment
- References and author index
- Index to symbols
- Index to organisms
- Index to water bodies
- Subject index
Summary
Having described the nature of the incident radiation flux presented to the aquatic biosphere and the influences to which the light is subject within the water, we shall now consider the kind of light field that results. We shall begin, in this chapter, by examining the ways in which the properties of this light field are studied. The physical definitions of these properties are given in Chapter 1.
Irradiance
Irradiance meters
The most frequently and easily measured property of the underwater light field is irradiance. Knowledge of this parameter is valuable, not only because it provides information about how much light is available for photosynthesis, but also because irradiance plays a central role in the theory of radiation transfer in water. An irradiance meter, since it is meant to measure the radiant flux per unit area, must respond equally to all photons that impinge upon its collector, regardless of the angle at which they do so. With any given meter this can be tested by observing the way in which its response to a parallel light stream varies with its angle to that light stream.
As the angle of the radiant flux to the collector changes, the area of the collector projected in the direction of that radiant flux changes, and the proportion of the flux intercepted by the collector changes correspondingly (Fig. 5.1). Thus, the response of an irradiance meter to parallel radiant flux (wider than the collector) should be proportional to the cosine of the angle (θ) between the normal to the collector surface and the direction of the flux. An irradiance collector which meets this criterion is known as a cosine collector.
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- Information
- Light and Photosynthesis in Aquatic Ecosystems , pp. 112 - 128Publisher: Cambridge University PressPrint publication year: 1994
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