Other Fits
Line Intensity Fitting
Line intensities can also be fit, which makes sense in three
contexts:
- Where absolute intensities have been measured and a fit can
therefore determine the transition moment.
- Relative intensities have been measured of two or more bands,
and the relative transition moments are required.
- A series of relative intensity measurements have been made,
and the population distribution are required.
The essential procedure is the same as for
line position fitting, except that the line intensities replace
the positions in the observations file. When fitting, the Fit type combo box should be
set to "Intensity" or "Fractional Intensity"
rather than "Line", and you will want to make sure that
only parameters affecting the intensity are floated. (In principle
this will be all parameters, but you will normally want to float
the transition moments and temperature only.)
Unless measured intensities are particularly precise, I recommend
using "Fractional
Iintensity". This forces the estimated error for each
intensity to be equal to the intensity itself, and is equivalent
to errors that are a constant fraction of the measured intensity.
This is often a better match for errors in typical intensity
measurements than a standard fit, as intensities are often subject
to large errors, and the most meaningful fit is often to the
trend. The average error given by these fits should be
interpreted as an average fraction of the intensities, so an error
of 0.1 should be interpreted as individual transitions fitting on
average to 10% of their intensity.
To fit populations set the required levels up
as described in
Non-Boltzmann Populations;
this then provides a parameter for each level of interest in the
manifold that can be floated as for other parameters. Again you
will normally want to float these population parameters only.
Energy Level fits
This is essentially a special case of a line
position fit. To force the observed value in a given line in the
input file to be treated as an energy level, rather than a
transition frequency, replace
J, S and
# for the unwanted state with
"-" and leave the manifold field blank. It is also possible to
force this for a complete file from the
Log
Window. If HITRAN or JPL line catalog files are used as
input, then these have energy level information in them and
selecting
EUpper or
ELower in the log window
will cause the state energy to be worked out (using the line
position and lowers state energy for
EUpper). For other
file formats the values given in the file must be the energy
level.
Procedures