Lowtran in Python

LOWTRAN7 atmospheric absorption extinction model. Updated to be platform independent and easily accessible from Python and Matlab.

The main LOWTRAN program is 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

Lowtran requires a Fortran compiler and CMake. 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 any one of Windows Subsystem for Linux, MSYS2, MinGW to get Gfortran or use Intel oneAPI.

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 Python 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.

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:

   runtests('lowtran')

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.