Radiation Fluxes
in Natural
Environments 11
Before beginning a detailed discussion of radiant energy budgets of plants,
animals, canopies, and soils, we need to determine what information
will be required and how to obtain that information. An environmental
biophysicist may approach the study of radiant energy exchmgg in two
different ways. For thefirst, detailed observations of radiant flux densities
--to and from an organism are needed to compute a detailed energy budget.
--.
These detailed observations must be obtained by direct measurement at
the time the energy budget is being determined. The-second type of study
simulates the behavior of parts of_ann<:osystem. Knowing the exact value
-of a radiant flux density may not be as important as having the correct
relationship among variables. Models of the fluxes, extended from the
basics covered in Ch. 10, are used for studies of the second type. The
models can be counted on to give reasonable estimates (f 10%) of average
flux densities, but they are usually not adequate as substitutes for careful
field measurements of radiant fluxes for detailed energy budget studies.
This chapter presents models for estimating solar and thermal rad@t
-
fluxes in the natural environment.
- - _ _
Streams of solar radiatioi received by an organism are
1. beam, or.direct.radiation, directly from the sun,
2. diffuse radiation, scattered by sky and clouds, and
3. reflected -. radiation from terrestrial objects.
Separating solar radiation into at least this many components is necessary because the amounts and directional characteristics are different
for each. Beam radiation is highly directional and irradiance at a surface
is determined using Lambert's cosine law (Eq. (10.3)). Diffuse sky and @ z Fdrrr$
reflected ground radiation are scattered from all directions. The diffuse
&adiance at a surface is computed by integrating the radiance o G -
roundings using the procedure given in Ch. 10. To find the ... components
of-the solar radiation buAet the following need to be known: the flux
C
, densikof solar radiation perpendicular to the solar beamYhthe anp15: the
beam makes with the absorbing surface, and the flux densities of sky
diffuse and ground reflected radiation.
in Natural
Environments 11
Before beginning a detailed discussion of radiant energy budgets of plants,
animals, canopies, and soils, we need to determine what information
will be required and how to obtain that information. An environmental
biophysicist may approach the study of radiant energy exchmgg in two
different ways. For thefirst, detailed observations of radiant flux densities
--to and from an organism are needed to compute a detailed energy budget.
--.
These detailed observations must be obtained by direct measurement at
the time the energy budget is being determined. The-second type of study
simulates the behavior of parts of_ann<:osystem. Knowing the exact value
-of a radiant flux density may not be as important as having the correct
relationship among variables. Models of the fluxes, extended from the
basics covered in Ch. 10, are used for studies of the second type. The
models can be counted on to give reasonable estimates (f 10%) of average
flux densities, but they are usually not adequate as substitutes for careful
field measurements of radiant fluxes for detailed energy budget studies.
This chapter presents models for estimating solar and thermal rad@t
-
fluxes in the natural environment.
- - _ _
Streams of solar radiatioi received by an organism are
1. beam, or.direct.radiation, directly from the sun,
2. diffuse radiation, scattered by sky and clouds, and
3. reflected -. radiation from terrestrial objects.
Separating solar radiation into at least this many components is necessary because the amounts and directional characteristics are different
for each. Beam radiation is highly directional and irradiance at a surface
is determined using Lambert's cosine law (Eq. (10.3)). Diffuse sky and @ z Fdrrr$
reflected ground radiation are scattered from all directions. The diffuse
&adiance at a surface is computed by integrating the radiance o G -
roundings using the procedure given in Ch. 10. To find the ... components
of-the solar radiation buAet the following need to be known: the flux
C
, densikof solar radiation perpendicular to the solar beamYhthe anp15: the
beam makes with the absorbing surface, and the flux densities of sky
diffuse and ground reflected radiation.