See also: http://www.libradtran.org/doku.php?id=basic_usage and http://www.libradtran.org/doku.php?id=faq
To run an input file and write the output into a file do:
uvspec < input_file.inp > output_file.out
If irradiances are calculated, the standard output includes the following columns:
If you are only interested in irradiances you may use the option
output_user lambda edir edn eup
which gives you only the 4 columns that you need.
Radiances are calculated if the umu and phi are specified, e.g.
umu -1 -0.886 -0.5 # viewing zenith angle phi 0 45 90 135 180 # viewing azimuth angle
The output format then looks as follows:
lambda edir edn eup uavgdir uavgdn uavgup phi(0) ... phi(m) umu(0) u0u(umu(0)) uu(umu(0),phi(0)) ... uu(umu(0),phi(m)) umu(1) u0u(umu(1)) uu(umu(1),phi(0)) ... uu(umu(1),phi(m)) ... ... ... ... ... umu(n) u0u(umu(n)) uu(umu(n),phi(0)) ... uu(umu(n),phi(m))
Here u0u is the azimuthal averaged radiance (0th Fourier mode of radiance field) and uu are the radiances (I(mu, phi)).
In order to read the radiances in phython the easiest is to cut off the two first lines, which can be done on the shell as follows
uvspec < input_file.inp | gawk 'NR>2' > output_file.out
The output file is piped into gawk, which writes only lines with line number (NR) greater than 2.