SRFM 1.0.4

The Scattering Reference Forward Model

SRFM

Welcome to SRFM, a package designed to manage satelitte data and perform retrievals.

Components

This is a Python package. Apart from pure python routines, the package contains three external codes - RFM, DISORT and mie_ewp. These codes are in Fortran and are compiled as python modules with numpy-f2py.

DISORT

The package contains the DISORT code as an external module. DISORT is a code that solves the radiative transfer equation (with scattering). The original code, which is in single precision and mostly fixed-form Fortran, has been updated to double precision. Both versions - single and double precision - are present. Slight modifications to DISORT were performed in its printing routines.

RFM

The code contains the Reference Forward Model (RFM) which calculates gas absorption in the atmosphere. Small changes with respect to the original RFM were made, such as 6-digit filenames for better precision and a few scripts for compilation into Python modules and capturing the output.

mie_ewp

The mie_ewp module calculates Mie scattering on particles. The main outputs are the extinction coefficient, single scatter albedo, the scattering phase function and its Legendre polynomial expansion for a given particle size distribution and composition in a given wavenumber/wavelength range.

Installation

Installation through pip should compile the Fortran extenstions with numpy on the user's system. To install, pip install srfm should work. Only source (sdist) is provided. Platform specific wheels are currently not shipped. If installation fails, the second option is to download the sdist and manually recompile the Fortran routines and debug - see below.

Supported platforms and prerequisites

SRFM targets every currently supported CPython release (3.10–3.13) on Linux and Windows. The Fortran components require a Fortran compiler (gfortran works well cross-platform), plus Meson and Ninja. The helper scripts install Meson and Ninja automatically through pip if they are missing, and the build metadata in pyproject.toml lists them as build requirements so pip install also bootstraps them in isolated build environments.

The runtime Python dependencies are declared in the pyproject.toml. Building the Fortran extensions requires numpy (for numpy.f2py), meson, and ninja. You only need to install those manually when working outside of the supplied helpers.

Building and packaging (multi-platform)

The repository root contains both a GNU Makefile (for Linux/macOS) and a Python driver (tools/build_package.py) that offer the same targets so that Windows users do not have to rely on make. Every workflow below automatically installs Meson/Ninja if they are missing.

Linux / macOS quick start

make native          # compile the Fortran extensions
make dist            # rebuild wheel + sdist under dist/
make install         # install from the freshly built artifacts

or

python build_extensions.py      # builds Fortran extensions 

Windows (PowerShell or Command Prompt)

py tools/build_package.py native
py tools/build_package.py dist
py tools/build_package.py install

Both entry points accept optional arguments such as COMPONENTS="mie disort_double" for make or --components mie disort_double for the Python helper when you want to rebuild only a subset of extensions. Compilation logs continue to be stored in src/srfm/build.log. python clean_srfm.py removes every compiled artifact.

To succeed, the compiler needs the ".f2py_f2cmap" file in src/srfm/RFM. Do not delete that!!! That file ensures that correct types are enforced during the compilation. For example, it forces things such as real(kind=r8)/double precision to emit C doubles during the f2py run. If the file is deleted, the C emits single precision values and underallocates arrays, leading to malloc() errors.

Installing from dist/

If installing manually, first generate the sdist or wheel on your machine (as described above) and then install from the local dist/ directory by pip install sdist-or-wheel-filename When you run pip with the local dist/ folder as an extra index, it automatically inspects the platform/Python tags exposed by each wheel and falls back to the source distribution when there is no suitable wheel. Alternatively, run

python -m pip install --no-index --find-links dist SRFM

The tools/install_from_dist.py wrapper runs the same command and performs the Meson/Ninja bootstrap step first. This works unchanged on Linux and Windows.

Verifcation

If the srfm was successfully installed, you should be able to import it in Python (import srfm). If this import fails, then so has your installation. A common error is not having correctly compiled the Fortran extensions, as a result of which they can't be imported. A hopefully helpful error message will be printed.

Usage

To use this code as a traditional radiative transfer model program, the package has with an example. The example can be found at: INSERT LINK

To run this example, you need to:

1. Successfully install srfm (see above).
2. If required (probably yes), obtain the external dependencies as described below.
3. Modify any paths in the driver table (i.e. where to save results, where your external dependencies are on your computer, etc. Note that you need line parameters or cross-sections for all gases listed in the gases section of the RFM inputs.
4. Run the program run_srfm.py
5. Your results will be stored in the folder you specified in the driver table.

Users are recommended to use this example as a template to develop their own.

Alternatively, the package can be easily imported by from srfm import * or import srfm Modules can also be imported individually. In this case, the package works and should therefore be treated as a standalone python package with its modules and functions, which the user may use as required.

External dependencies

All current package dependencies are standard packages. Installation requires gfortran, meson and ninja, the latter two being installed automatically at installation. Usage requires packages listed in pyproject.toml:

numpy, pandas, scipy, netCDF4, matplotlib, cartopy, numba, psutil and 
mergedeep

These should be installed automatically by pip at installation.

Besides those, there are several external dependencies. The prime among those is line transition parameters for the line-by-line radiative transfer calculation. The default option is to use line by line parameters from HITRAN. The transition parameters need to be downloaded separately and converted to a binary format that the code can efficiently use. A code to convert hitran database data to the binary file can be downloaded here. For molecules not in the HITRAN line parameters database, absorption cross sections may be used. These can also be downloaded from the HITRAN website (and do not need to be converted). The location of both the line parameters file and the cross-sections folder are specified in the driver table when running the program as paths (see example). Other sources of line parameters are possible, but in that case, care should be taken to convert them to the appropriate format.

Next, the scattering calculations require complex particle refractive indices. The ARIA database of refractive indices is shipped with the code and is the default option (no need to do anything by the user). Alternative sources are permitted if they keep the same format. Refractive indices to use are again specified in the driver table (see exmaple).

Documentation

The full documentation can be found at: https://srfm.readthedocs.io/en/latest/. This is a Sphinx-generated documentation from function docstrings, i.e. equivalent information may be found in the docstrings within the code.

References

The package paper has been published at: INSERT LINK