Lowtran in Python

LOWTRAN7 atmospheric absorption extinction model. Updated by Michael Hirsch to be platform independent and easily accessible from Python ≥ 3.6 and Matlab.

The main LOWTRAN program has been made accessible from Python by using direct memory transfers instead of the cumbersome and error-prone process of writing/reading text files. xarray.Dataset high-performance, simple N-D array data is passed out, with appropriate metadata.

Gallery

See below for how to make these examples.

Install

You will need a Fortran compiler. gfortran is one suitable compiler. We use f2py (part of numpy) to seamlessly use Fortran libraries from Python by special compilation of the Fortran library with auto-generated shim code.

1. If a Fortran compiler is not already installed, install Gfortran:

   • Linux: apt install gfortran
   • Mac: brew install gcc
   • Windows use MSYS2 or MinGW to get Gfortran. Windows only: from Powershell:

   echo "[build]`ncompiler=mingw32" | Out-File -Encoding ASCII ~/pydistutils.cfg
   

   Note: Cygwin is essentially obsolete due to Windows Subsystem for Linux. Cygwin is broken for Numpy and Gfortran and general.

2. Install Python Lowtran code

   pip install -e .
   

Examples

In these examples, you can write to HDF5 with the -o option.

We present examples of:

• ground-to-space transmittance: TransmittanceGround2Space.py

  

• sun-to-observer scattered radiance (why the sky is blue): ScatterRadiance.py

  

• sun-to-observer irradiance: SolarIrradiance.py

  

• observer-to-observer solar single-scattering solar radiance (up-going) with custom Pressure, Temperature and partial pressure for 12 species: UserDataHorizontalRadiance.py

• observer-to-observer transmittance with custom Pressure, Temperature and partial pressure for 12 species: UserDataHorizontalTransmittance.py

• observer-to-observer transmittance: HorizontalTransmittance.py

  

Matlab

Matlab users can seamlessly access Python modules, as demonstrated in RunLowtran.m and lowtran_transmission.m.

Here's what's you'll need:

1. Setup Python ↔ Matlab interface.

2. Install Lowtran in Python as at the top of this Readme.

3. From Matlab, verify everything is working by from the lowtran/ directory:

   runtests('tests')
   

Notes

LOWTRAN7 User manual Refer to this to understand what parameters are set to default. Currently I don't have any aerosols enabled for example, though it's possible to add them into the code.

Right now a lot of configuration features aren't implemented, please request those you want.

Reference

• Original 1994 Lowtran7 Code
• LOWFIL program in reference/lowtran7.10.f was not connected as we had previously implemented a filter function directly in Python.
• LOWSCAN spectral sampling (scanning) program in reference/lowtran7.13.f was not connected as we had no need for coarser spectral resolution.

Fortran (optional)

To compile Fortran code standalone (without Python):

ctest -S setup.cmake -V