The most significant new feature in MODTRAN® 6 and hence PcModWin is the capability to
do linebyline (LBL) transmission and radiance calculations.
This means MODTRAN® calculations are applicable for laser calculations at all pressures at a
spectral resolution determined by the HITRAN database. This is a significant enhancement
over MODTRAN 5 with the 0.1 to 0.2 cm1 capability.
Hence there is no longer the need to us FASCOD for LBL calculations. Please see test
case 1.5.11 AnLBLTemplate below for instructions on LBL calculations
The other changes from previous versions of MODTRAN are the input file format, and the
programming language used for the source code. Previously, the code was written in
FORTRAN with formatted FORTRAN input/output files. The current version is a combination
of C++ and FORTRAN source code. The input can be in either the older FORTRAN format,
i.e. tape5 etc., or in JSON format.
These changes are transparent to a PcModWin user.
The material here is taken from MODTRAN® 6.0.0 User's Manual (revision 5),
performed under US Government Contract No. FA945312C0262; Data Item A007, July 2016.
A. Berk, J. van den Bosch, F. Hawes, T. Perkins, P.F. Conforti, G.P. Anderson, R.G. Kennett,
and P.K. Acharya.
A summary of new features includes:

Reformulating the band model parameters and radiative transfer formalism to increase
the resolution of MODTRAN spectral calculations to 0.1 cm^{1};
 Increasing the topofatmosphere solar database resolution to 0.1 cm^{1};

Introducing Fontenla topofatmosphere solar irradiance data;
SUNp1med2irradwn_Normt.dat is now the default.

Incorporating code interface changes between MODTRAN and DISORT to
increase its speed and accuracy of multiple scattering calculations;

Upgrading MODTRAN to perform spectral radiance computations for auxiliary molecules
(by including their concentrations and spectral parameters) that are not part of the
traditional MODTRAN database; band models are provided for all HITRAN molecular species;

Incorporating the effect of a thin layer of water, which can either simply wet the
ground or accumulate on it, on radiance computations;

Adding the capabilities to model a boundary layer aerosol whose extinction coefficient
obeys the Angstrom law or to modify the extinction of a model aerosol with an Angstrom law perturbation;

Adding the capability to determine the spherical albedo and reflectance of the
atmosphere and diffuse transmittance from a single MODTRAN run;

Adding the ability to include only the solar contribution to multiple scattering
and ignore the thermal component where it is not significant;

Adding an option to write spectral output in binary, and a utility to convert
the binary output to ASCII;

Upgrading the MODTRANDISORT interface so that only a single parameter
(MXCMU in routine disusr_mod.f90) needs to be modified to change the maximum
number of streams available for DISORT runs.

Adding dithering of the solar angle in cases where the DISORT particular solution
to the solar problem was unstable.
 Adding option to save and reuse DISORT scattering data.
 Adding .wrn files, and modifying comments, warnings, and errors to have a common format.
 Adding separate flux and atmospheric correction data, .acd, binary output files.

Adding option to model line center data via 2 pairs of absorption coefficient and
line spacing band model parameters.

Introducing a much improved algorithm for computing the finite bin Voigt transmittance.

Adding option to use distinct temperature grid data for each auxiliary (Y) species.

Adding atmospheric correction data to the channel spectra output.

Adding path geometry output files named
_pth (which can be used as path geometry input files by renaming the
files without the underscore).
 Adding thermal scatter as a DISORT run spectral output.

Replacing the spherical refractive geometry package with an iterative circular
arc algorithm for improved accuracy.
 Adding H2CH4 and CH4CH4 collision induced absorption features for
modeling extra terrestrial planet atmospheres.
AnLBLTemplate
This file was added to the set of test cases to serve as a template for doing
linebyline (LBL) calculations. We recommend you start with this case and modify
it to meet your specific requirements.
It is for a slant path geometry, using a MidLatitude atmospheric model.
It calculates radiance with scattering over the 0.7 to 1.2 μm spectral interval
(i.e. visible to near IR). It includes multiple scattering using the Isaac 2 stream algorithm.
Because of scattering and spectral interval, this calculation may take several hours to complete.
For most applications, you will do calculations over a much smaller spectral
interval which will significantly reduce the time. However, keep the following
"rules of thumb" in mind:
 Multiple scattering is very important in the visible spectral region;
 Less important in the 1 to 3 μm region;
 And NOT a contributor beyond 3.5 μms.
Consequently, we recommend:
 Visible region, use multiple scattering, DISORT scattering algorithm with 4 or more streams;
 12 μm, use multiple scattering, DISORT scattering algorithm with 2 streams;
 23.5 μm, use multiple scattering, Issaac scattering algorithm with 2;
 Beyond 3.5 μm, NO multiple scattering is needed.
An LBL calculation requires three major changes to a "standard", e.g. MODTRAN® 5 file
as shown in the figures below.
Also, keep in mind that an LBL calculation may generate large files depending on
the options selected. For example, the *_highres.csv file may have over 1,000,000 lines
if you cover a 1000 cm^{1} spectral region.
Three are three parameters that must be set to do an LBL calculations. They are:

Select "Line by Line" for the Calculation Option on the first input screen as shown
in the figure immediately below.
 Input the Number of LBL Spectral Points (NLBL) on the first input screen.
This is also shown in the figure below. NLBL is the integer number of spectral
points in each 0.1 cm^{1} bin at which LBL calculations are performed.
The default is 100 corresponding to 0.001 cm^{1} spacing. 100 is used in
this test case. The figure below with data from the
AnLBLTemplate*_highres.csv file demonstrated the effect of setting NLBL = 100.

Select the LBL2013 Band Model on the second input screen as shown in the next figure.
The band mode file determines the spectral resolution of the MODTRAN® calculation.
For example: 01_2013.bin is for 1 cm^{1} resolution;
05_2013.bin for 5 cm^{1}; and p1_2013.bin for 0.1 cm^{1}.
The next set of figures are plots of the AnLBLTemplate.ltn calculation.
Please NOTE, the plots in the first two figure are at 0.1 cm^{1} spectral resolutions.
These correspond to the data in *.tp6, *.tp7, MODOUT 1, MODOUT2 and *.csv files.
The high resolutions data is given in *_highres.csv.
These files can be found in the PcModWin/bin and PcModWin/usr/output directories.
ANTemplate  0.1 cm^{1} Resolution Plot
ANTemplate  Expanded 0.1 cm^{1} plot of figure above
High resolution data (determined by the NLBL parameter)
Click here to view PcModWin 5.3
enhancements.
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overview.
* The MODTRAN5® trademark is being used with the express permission of the owner,
the United States of America, as represented by the United States Air Force.