Dear Colleagues,

you receive this eMail because you are either a user of the radiative
transfer package libRadtran or because we think that you might be
interested in this information. Should you not be interested in
receiving further information, please let us know.

Attached to this eMail is the 17th libRadtran Newsletter. The main
issue of this Newsletter is to announce the new version,

           *** libRadtran 2.0.2 ***

which includes some improvements and bug fixes compared 
to version 2.0.1

Let us first wish you all a Merry Christmas and a happy  and successful
new year! 

Bernhard Mayer, Claudia Emde, Arve Kylling, and Josef Gasteiger

/*----------------------------------------------------------------
 * libRadtran Newsletter No. 17
 *
 * December 24, 2017
 *
 * Claudia Emde   (claudia.emde_at_lmu.de)
 * Bernhard Mayer (bernhard.mayer_at_lmu.de)
 * Arve Kylling   (arve.kylling_at_gmail.com)
 * Josef Gasteiger (josef.gasteiger_at_univie.ac.at)
 *
 * ### More info: http://www.libradtran.org ###
 *----------------------------------------------------------------*/

Dear libRadtran users,

merry Christmas and a good start into the New Year! 

In an attempt to revive an old tradition, a new libRadtran
version is released as a Christmas gift. The change in version
number is not that big, and the changes are neither. Nevertheless,
there is a number of new features and bug fixes.

We have to admit first that we actually forgot to send a newsletter
when we released version 2.0.1. This version wasn't actually too
different from 2.0. The main purpose for giving it a name was to
create a version which was consistent with the new libRadtran
reference publication:

C. Emde, R. Buras-Schnell, A. Kylling, B. Mayer, J. Gasteiger, U. Hamann,
J. Kylling, B. Richter, C. Pause, T. Dowling, and L. Bugliaro.
The libradtran software package for radiative transfer calculations (version 2.0.1).
GMD 9(5):1647-1672, 2016

When using libRadtran in a publication, please reference this publication plus
preferably the original one as well (Mayer and Kylling, 2005), since the new
paper is essentially a "delta" describing changes and new features that were added
between 2005 and 2016.

But now for the news: 

 *** Major changes:
 
 * Absorption lines importance sampling (ALIS) is now available in the public release.

   ALIS allows efficient spectral calculations of (polarized) radiances 
   using the Monte Carlo solver MYSTIC (1D). The trick is to trace
   photons only for one wavelength and to transfer the results to
   the neighboring wavelengths. This is done in a physically and
   mathematically correct manner and has the big advantage that
   the noise of all wavelengths is not independent but correlated.
   That way, e.g. tiny absorption features such as from NO2
   around 400 - 500nm can be simulated accurately and quickly.
   There is just on caveat: The spectral variation of the cloud phase
   function / phase matrix is neglected. You won't be able to
   simulate a colorful rainbow with ALIS.

   The option is switched on with "mc_spectral_is". For details refer to: 

      C. Emde, R. Buras, and B. Mayer. ALIS: An efficient method to
      compute high spectral resolution polarized solar radiances using
      the Monte Carlo approach. J. Quant. Spectrosc. Radiat. Transfer,
      112(10):1622-1631, 2011.

   Also have a look at the following examples:
     UVSPEC_MC_SPECTRAL_REPTRAN.INP (default REPTRAN absorption
     parameterization, spectral albedo file for vegetation)

     UVSPEC_MC_SPECTRAL.INP (very high spectral resolution,
     line-by-line absorption coefficients)

 * The REPTRAN parameterization has been extended to more satellite
    channels including GOES, HIMAWARI, MODIS, MSG4, and Sentinel-2a.
    In order to use these make sure to download the moste recent version of the
    REPTRAN data (December 24, 2017) from the Download area.
 
    The examples UVSPEC_REPTRAN_THERMAL.INP and UVSPEC_REPTRAN_CHANNEL_THERMAL.INP 
    show how to set up an input file to simulate radiances for a
    specific satellite channel. 

 * MYSTIC includes a new option to calculate box airmass factors "mc_boxairmass".
    The example UVSPEC_MC_BOXAIRMASS.INP demonstrates how it is used. 

 * Calculations with disort solver and BRDF are now more efficient,
    because a highly time consuming self-check has been disabled. The
    computational time is reduced by a factor of 5.

 * Please note that the packages "netcdf" and "GSL" are now mandatory
   to build uvspec. In former releases it was possible to build uvspec   
   without these packages but only with major restrictions.


*** Bug fixes: 

 * The option "aerosol_set_tau_at_wvl" did not work correctly. This has been fixed.  

 * Fixed a bug that occurred when "aerosol_angstrom" and
   "aerosol_king_byrne" were used in combination with the absorption parameterization REPTRAN.

 * Fixed formula for aerosol_king_byrne in documentation (reported by Jethro Betcke). 

 * GUI: Fixed bug with 'from matplotlib.axes
   import_process_plot_var_args' due to change in matplotlib location
   of this module.


*** Reminders:

 * For simulations with clouds and/or aerosols we strongly recommend
    to get the additional optical properties data from the Download area,
    which are much more accurate than the defaults, in particular for radiance simulations. 


And now, have fun!