HITRAN on the Web

Guest   |  

Launch simulation

The page is intended for setting the parameters of the simulated spectrum and for launching the simulation process with the specified parameters.
Let's consider in details the form presented on this page (Fig. 1).

Fig. 1. The form of spectrum simulation  launching

Molecule. Drop-down list of molecule selection. For the selected molecules to the right of the list are shown the default values of Lorentz half-widths (Lenv and Lself) and the temperature dependence exponent (Nt) of the Lorentz half-width. Standard values are used to construct the contours of those lines for which the values of these parameters are not available.

Simulation type. Drop-down list of simulation types: the list of spectral lines or one of the spectral functions described in Generalities/Spectral functions.

Select isotoplogues. The table shows available isotopic modifications of selected molecule and essentisal properties of them. The left column of the table contains the checkboxes for selection of isotopologue. The checkbox in the table header selects or deselect all isotopologues. At least one isotopologue should be selected.

Spectral lines selection parameters. The range of wavenumbers where the spectrum is simulated and the cut-off on intensity (spectral lines with intensities lower than indicated here, are not taken into account).Note that the wavenumber range should be no wider than the Union of the ranges of the selected isotopologues, and the line intensities are weighted according to the natural terrestrial isotopic abundances and changed according ambient temperature.

The parameters of the environment. Temperature T and pressure P. The default temperature is set equal to 296 K, and default pressure is set to 1 atm. The temperature should get into the narrowest range of acceptable temperatures for the selected isotopologues.

The following sets of parameters have sense and displayed on the page only if as a Simulation type one of the spectral functions is selected.

Contour parameters. The parameters required for creation of the spectral line profile (see Generalities/Line profiles). The drop-down list Line shape allows you to select one of  available profile types. The Wing parameter specifies the length of the simulated wing of spectral line, expressed by the number of half-widths (how the half-width is calculated for different profile types, is described in the same section of Generalities). The parameter Calculation step specifies the step by wavenumber in cm-1, which is used for calculation of the spectral functions values. This step is calculated automatically, based on the fact that the half-width has 20 points, but you can also specify it manually. Since the half-width of the lines depends in general case from WNmax, T, P and the type of line profile, when you change any of these settings the step value is changed. It is recommended before starting the simulation to round it to values with a reasonable number of digits after the decimal point.

The Device parameters allow to take into account the influence of the device on a simulated spectrum. If as apparatus function (AF) selected "no influence of the device", then the simulated spectrum is a  high resolution spectrum. With any other choice the resulting spectrum will be low resolution spectrum. In the simulation of the low resolution spectrum must be set to the correct value of the appratus resolution AR in cm-1 and the length of the wing of apparatus function in AR. For rectangular and triangular apparatus function the value of the last parameter is ignored. More detailed information about simulation of low resolution spectra is in paragraph Convolution of spectra of the Generalities.

For simulation the Transmittance, Absorption and Radiance should be set the value of the Optical path L in m.

Registered users have access to an additional set of parameters Simulation optoins, where they can choose where to save the simulation results: in a temporary storage or in an user's archive. If the user's archive is selected , it is possible to run simulations in batch mode. More detailtd these features are described on the first page of this section.

The simulation process starts by pressing the button Start simulation.

At the first visit of the page in the user's session all simulation parameters take the default values. When you visit the page after the simulation is complete, the settings of the last simulation are saved on the page. To return to the default settings, use the Reset parameters button.