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Glossary of Solar Radiation Resource Terms |
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Other relevant glossaries
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Barometer -
an instrument that measures atmospheric pressure.
Barometric Pressure -
the pressure (force per area) created by the weight of the atmosphere, measured by
a barometer. At higher elevations, the atmospheric pressure is lower because there
is less air.
Beam Radiation -
synonym for direct normal irradiance,
the amount of solar radiation
from the direction of the sun.
Click Shining On (Figure 3) to see solar components
Bias Limit -
An indication of the average deviation of the predicted, or true values,
from the measured values. Typically expressed as twice the mean bias error
(MBE):
where:
yi is the ith predicted, or true value
xi is the ith measured value
N is the number of observations.
Bidirectional Reflectance -
A term for the amount of reflected radiation compared to the amount of
incident radiation, or
albedo,
of a surface. The surface is not perfectly
specular. That is, the reflected intensity is not at the same angle with
respect to the surface normal as the incoming rays, nor are the two
intensities necessarily equal (in crude terms, when light bounces off the Earth,
some of it is absorbed and the rest of it bounces "funny", not as it would off a mirror).
Biomass -
plants, crops, and trees; converted by solar fuel technologies into
fuels and byproducts. See the Biomass Resource
Information Clearinghouse.
Bird Clear Sky Model -
named after Dr. Richard Bird, a scientist at
SERI (
NREL), this physical model uses properties of the
atmosphere such as albedo,
turbidity, and
precipitable water to determine the amount
of solar radiation striking the earth's
surface from a cloudless sky.
Blackbody -
the theoretical "perfect" absorber of light at all wavelengths. As blackbodies heat up,
they emit a characteristic double-exponential light frequency (energy) curve,
which is imperfectly seen in nature. For example, Figure 2 from
Shining On
below shows the imperfect blackbody curve of the sun and the chunks that are ripped from it
by the earth's atmosphere.
Bolometer -
the most sensitive thermometer known to science. Invented
in 1880 by astronomer Samuel P. Langley, the bolometer is used to measure
light from the faintest stars and the sun's heat rays. It consists of a
fine wire connected to an electric circuit. When radiation falls on the
wire, it becomes very slightly warmer. This increases the electrical
resistance of the wire. The difference in conductivity is proportional to
the incident irradiance.
BORCAL -
(Broadband Outdoor Radiometer CALibration)
A method of calibrating
pyrheliometers and
pyranometers based on the summation technique at the
Solar Radiation Research Laboratory (SRRL).
Up to three days of clear-sky
solar irradiance measurements taken at 30-second intervals from sunrise to
sunset are used to compute the individual radiometer responsivities.
For pyrheliometer calibrations, the reference direct normal irradiance is
measured with an electrically self-calibrating absolute cavity radiometer
traceable to the
World Radiometric Reference (WRR). The individual
pyrheliometer responsivity is computed as the mean ratio of the signal from
the pyrheliometer (microvolts DC) to the reference irradiance (Watts per
square meter) for each of the 30-second data samples.
Pyranometer responsivities are computed from the ratio of the signal from
each pyranometer (microvolts DC) to the reference
global horizontal irradiance determined by the
direct normal irradiance (measured with an
absolute cavity radiometer) and the simultaneous
diffuse horizontal irradiance
(measured by a reference pyranometer placed under a solar-tracking
shading disk):
Global Horizontal = Direct Normal x cos(Z) + Diffuse Horizontal
where
Z = Solar Zenith Angle at the time of measurement.
The reference pyranometer is calibrated prior to use in a BORCAL event by
means of the Shade Calibration Technique.
Bright Sunshine -
when the sun casts an obvious shadow or when a
Campbell-Stokes sunshine recorder
is recording. The lower limit for bright sunshine (based on a Campbell-Stokes recorder)
is between 70 W/m2 (very dry air) and 280 W/m2 (very humid air).
Broadband Solar Irradiance -
theoretically the solar radiation arriving at
the earth from all frequencies or wavelengths, in practice limited to the spectral range
of radiometers, typically from 300 nm to 3000 nm
wavelength. Meteorologists refer to this band as
short-wave radiation.
BSRN -
the worldwide Baseline Surface Radiation Network,
or the program that manages it.
Btu -
British Thermal Unit, the amount of energy required to raise one pound of water one
degree Farenheit at 60°F, equivalent to 1055
joules or 252.1
calories.
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