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Two Way Transmission Calculations

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Leigh Fletcher edited this page Apr 16, 2019 · 3 revisions

In the thermal-infrared, contribution functions (identical to the Jacobians, or functional derivatives, for temperature) are calculated analytically at every step of a NEMESIS inversion, and output in the nemesis.cov or kk.out files. However, when we wish to calculate the two-way transmission in reflected sunlight, a more convoluted use of individual subroutines is required.

Editing the PATH File:

You’ll need to write your own .pat file and run CIRSdrv_wave. In the .pat file you’ll split up the atmosphere into N layers as usual and then list N reflatm calculations that calculate the two-way transmission (at your choice of incident and reflected angles) to the bottom of whichever layer (defined by layer) you want.

Defining a reflected atmospheric path requires editing the .pat file to include N blocks of the following (one for each layer in your model):

  • reflatm (this is the keyword)
  • angles followed by the incident and reflected angles and the number of the layer from which the reflection occurs (reflection happens at base of layer)
  • (no)cg Sets Curtis Godson flag as required
  • (no)absorb Sets absorption flag as required

Note also that the calculated transmission may depend on how you choose to divide up the atmosphere into layers - typically we'd use LAYTYP=1 to subdivide the layers in equal units of log(p).

Running CIRSdrv_wave:

For the reflecting atmosphere paths, CIRSdrv_wave will calculate the transmission at each level as a function of wavenumber/wavelength. The transmission=0.5 level can then be estimated. Alternatively, the natural logarithm of the transmission provides the optical depth, allowing you to plot the unity optical depth level.

CIRSdrv_wave will require the following inputs:

  • An operational filename (i.e., the root of your .pat file)
  • ISPACE in wavelength or wavenumber.
  • Whether to use ktables of line-by-line.
  • Which planet you're modelling (to estimate solar distance).
  • An option to use fast post-calculation or slow regridding (choose the former, which uses the wavelengths in your ktable).
  • Which scattering model to use: scloudwave11 is the one used in regular NEMESIS runs.
  • A surface temperature (not applicable to giant planets).

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