Yet a third spectral unit,
commonly used in spectroscopy, is wavenumber, the number of waves per cm: σ = ν/100c cm-1. Converting (1) to these
units gives
.
(13)
Again, the peak is where the derivative with respect to
wavenumber vanishes:
so
. (14)
The peak value is
. (15)
The spectral photon radiance is found by dividing Lσ
by the energy of a photon, 100hcσ:
. (16)
We next find the wavenumber at the peak of the spectral
photon radiance:
and . (17)
The peak spectral photon
radiance is
. (18)
Fig. 3 shows plots of Lσ and LσP for various temperatures. Note again the important difference between the spectral
radiance and spectral photon radiance.
Fig. 3 - Spectral
radiance, Lσ, (top) and the spectral
photon radiance, LσP, (bottom) as a function
of wavenumber, σ,
for various temperatures. The
small black dots indicate the wavenumber and value of the peak, at 10 K
temperature intervals. Note that
Lσ
and LσP have different wavenumber dependences. Although the peak wavenumber is
proportional to T for both
quantities, Lσ
peaks at a higher wavenumber than LσP. Furthermore, the peak
value of Lσ
increases as T 3,
whereas the peak value of LσP increases as T 2.
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Radiance: radiant flux radiated per unit area, per unit solid angle, per wavenumber
light with wavenumber between σ and σ + dσ
Radiance: radiant flux radiated per unit area, per unit solid angle, per wavenumber
light with wavenumber between σ and σ + dσ
Isotopes are forms of an element whose nuclei have the same atomic number, the
number of protons in the nucleus,but different atomic masses because they contain different numbers of neutrons.
Wavenumber cm-1: the number of wavelengths of light per centimeter
LINEPAK: The GATS spectral radiance and transmission software library. Performs detailed and accurate line-by-line modeling of molecular
absorption. Efficient and flexible, LINEPAK is at the heart of analysis systems for many major atmospheric remote sensing missions, including HALOE, SABER, LIMS, SOFIE, CRISTA, and CLAES.
Tangent Path: Model the transmission or radiance of a ray that
passes completely through the Earth's atmosphere but does not intersect the Earth. The path is specified by the tangent height, the
height at the point of closest approach to the surface. The pressure, temperature and vmrs of absorbing gases at each
altitude are chosen from a database of atmospheric states.
Slant path: Model the transmission or radiance of a ray
between two arbitrary points in the Earth's atmosphere. The points are specified by their heights and the zenith angle from one to the
other.
VMR: volume mixing ratio. The fractional number of molecules of a species in a volume.
Individual vmrs and their sum must be between 0 and 1.
If the vmrs sum to less than 1, the rest of the gas in the cell is assumed transparent.(Lineshapes for molecules with vmr less than 1 are air-broadened.)
Clicking this will display the data as text in a new browser window. Right-clicking will download the data file to your computer (recommended). These files can be extremely large depending on the spectrum simulated.
Clicking this will open a new browser window suitable for printing.
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Spectroscopy and remote sensing tools for researchers, teachers, and students
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Get priority use of advanced, state-of-the-art radiative transfer algorithms--the same ones used by NASA for many remote sensing missions. Subscribers gain access to large wavebands, multiple gases and cells, choice of units, radiance spectra, logo-free high-resolution graphics, data files, full tech support, and much more.
Temperature Offset: The model atmosphere (US_Standard, Tropical, etc.) determines the temperature, pressure and gas concentrations at each height in the atmosphere. To adjust the temperature from the model value, enter a temperature offset (from -50 to 50 K). The Atmosphere Browser tool displays the temperature profiles for the model atmospheres.
Atmosphere: An atmosphere contains profiles of temperature and gas concentrations at all altitudes. There are six system-supplied atmospheres for Earth and one for Mars. Custom atmospheres can be uploaded from the Atmosphere Browser.
Scale Factor for Gas Concentrations:
The model atmosphere (US_Standard, Tropical, etc.) determines the gas concentrations at each altitude. To adjust a gas concentration, choose a scale factor, from 0 to 1000. For example, to simulate an atmosphere with 20% more water vapor than the model, enter a scale factor of 1.2 for H2O. Note: while the model atmospheres are physically realistic, using large scale factors can produce unphysical situations where the gas abundance exceeds 100%. If this occurs, an error message will be displayed.
The atmosphere model (US_Standard, Tropical, etc.) determines the temperature, pressure and gas concentrations at each height in the atmosphere. To adjust a gas concentration, choose a scale factor other than 1 (from 0 to 1000). For example, to simulate a path with 20% more water vapor, use a scale factor of 1.2 for H2O. The Atmosphere Browser tool displays the temperature, pressure and gas mixing ratios for the model atmospheres..
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