====== Discrete ordinate method: Impact of intensity correction on cloudy radiance field at TOA ======

Calculate the radiance field for a cloudy atmosphere at the top of the atmosphere using the DISORT solver. Perform the calculation first for a pure Rayleigh atmosphere (only molecular absorption and scattering) and then include a cloud layer. What changes when you include the cloud? Use version 1 of disort with and without delta scaling (//rte_solver disort// including exactly the solution method derived in the lecture) and version 2 (//rte_solver disort2//) which includes a second order intensity correction method. Explain the results in general and the differences between the two solvers. 

Use the libRadtran input file and the plotting script from [[teaching:radiative_transfer:disort_nstr1|exercise 6]] to start.

A cloud layer is included by adding the following lines to the input file
<file bash disort1.inp>
wc_file 1d                 wc.dat
wc_properties              mie interpolate

</file>
More options to specify clouds are available in libRadtran, please check options starting with wc_ (water cloud) and ic_ (ice cloud) in the [[http://www.libradtran.org/doc/libradtran.pdf|libRadtran user manual]].

In order to use the cloud phase functions using Mie theory you have to copy some data into your libRadtran data directory
   cp /home/data/daten/public/rt-data/optprop_data/wc_new/wc.???.mie.cdf /local/libRadtran-1.5-beta/data/wc
If you do not have the permissions please let me know.   
 
The file wc.dat includes two columns to specify the liquid water content and the effective droplet size:
<file bash wc.dat>
# z [km]   LWC [g/m^3]  Reff[micrometer]
   3         0           0
   2       0.01         10
</file>
This file for example specifies a cloud layer between 2 and 3 km with a liquid water content of 0.01 and an effective droplet radius of 10 μm.

**Tips:**
 
In order to generate a line with umus from 0.01 to 1, you may use gawk: 
   gawk '{for (i = 1; i<=100; i++)  printf("%g ", 0.01*i)} ' dummy
where dummy is a file including one arbitrary line. 

In the plotting script (radfield_polar.py), the plot command should look as follows:
   contourf(phi*pi/180, arccos(umu)*180/pi, rad, N, cmap=cm.jet)
(theta should be in the range from 0° to 90°).   
 

====== Solution by Bettina, Nina and Fabian ======

=== Parameters in Config File ===
<file bash>
sza 30                   # solar zenith angle
source solar             kurudz_1.0nm.dat
atmosphere_file          us-standard
albedo 0.0               # Surface albedo
nstr                     16
wavelength               500
zout                     toa # defines viewing location at toa

#following param defines the angles, that we get results for e.g. the azumithally:
phi 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 ... 360
# and to look down from TOA we have only positive values:
umu 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 ... 1

# Note if we'd look up to the sky in case we are at the ground, we take 
# umu -1 -0.99 -0.98 -0.97 -0.96 -0.95 -0.94 ... -0.01


#In the following we introduce a water vapor file that configures a cloud layer between 2-3 km.
#this is done by the following paramters in libRadtran File:
wc_file 1D                 wc.dat
wc_properties              mie interpolate
</file>




{{:teaching:radiative_transfer:plot.disort1.toa.delta-off.cloud-on.png|}}
{{:teaching:radiative_transfer:plot.disort1.toa.delta-on.cloud-on.png|}}
{{:teaching:radiative_transfer:plot.disort2.toa.cloud-on.png|}}