pyCRTM - python interface to CRTM.

Bryan M. Karpowicz, Ph.D. - USRA/GESTAR/NASA 610.1 Global Modeling and Assimilation Office

This is a basic python interface to CRTM v2.3.0. I think it will generally serve my purposes and probably the purposes of other researchers needing a quick python accessible RT model.

The user interface is designed to be very similar to the python RTTOV interface. So, the user sets profiles, passes them to an object for a desired sensor, runs either the forward model/K-matrix, and pulls the brightness temperature/Jacobian/transmission/emissivity out of the object.

The user interface shouldn't change all that much, and hopefully won't get too broken if/when features are added.

This README has 4 parts:

1. Installation -- installing this library
2. Test/Examples -- describing test in testCases subdirectory
3. Python path etc -- how to use this library in a project.
4. Using the interface -- HOWTO/run through on how to use this interface

• Bryan Karpowicz -- August 16, 2019

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1. Installation:

Done via the setup_pycrtm.py script

Usage:

setup_pycrtm.py [-h] --install INSTALL --rtpath RTPATH --jproc JPROC [--arch ARCH] [--inplace]

setup_pycrtm.py: error: the following arguments are required: --install, --rtpath, --jproc 

Required:

• --install - Path where you want to install CRTM and coefficient files
• --rtpath - Directory where the CRTM tarball from EMC ftp site will be cached/downloaded if not present.
• --jproc - The number of threads to pass compiler

Optional:

• --arch select compiler/environment gfortran (gcc) and ifort (intel) have been tested.
• --inplace this will skip the building of CRTM, but instead just compile pycrtm interface and link to CRTM library specified in RTPATH.

In addition to installing CRTM this script will patch the source fix some in in/out structures that cause gfortran to fail (gfortran.patch), and will re-organize some null pointers to make the k-matrix thread safe for OpenMP (kmatrix.patch).

Example to install CRTM in this directory under a subdirectory lib/:

./setup_pycrtm.py  --install $PWD/lib/ --rtpath $PWD/lib/ --jproc 1

Once completed:

• $PWD/pycrtm.cpython-37m-PLATFORM.so <-- (will always reside here) f2py interface compiled by setup
• $PWD/crtm.cfg <-- Path where the CRTM coefficients are stored

Following the example the CRTM will be installed here:

• $PWD/lib/crtm/config.log <-- usual config associated with CRTM
• $PWD/lib/crtm/include <-- path to all compiled fortran modules
• $PWD/lib/crtm/lib/libcrtm.a <-- usual crtm static library
• $PWD/lib/crtm/crtm_coef <-- path to crtm_coefficients

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2. Tests/Examples:

A few test cases have been developed using input/output grabbed from the CRTM test program. Two basic scripts which will perform cases 1-4 (stored in $PWD/testCases/data/case[n].h5) from the CRTM test program on 4 OpenMP threads:

• $PWD/testCases/test_atms.py
• $PWD/testCases/test_cris.py These should just say Yay, and not produce any plots if successful.

The following scripts will do the same thing, only this time load up the same 4 profiles multiple times to further test threading with 10 threads (turn your laptop into a space heater more or less).

• $PWD/testCases/test_atms_threads.py
• $PWD/testCases/test_cris_threads.py These should just say Yay, and not produce any plots if successful.

The following scripts will run CRTM without aerosols or clouds:

• $PWD/testCases/test_atms_no_clouds.py
• $PWD/testCases/test_cris_no_clouds.py Right now w/ CRTM v2.3.0 there are differences between cases with zero cloud fraction, and with clouds turned off, so these test will fail, and generate plots.

3. Python path etc - needs work, but works for me at the moment:

Right now things aren't setup to install into a user's Python path. What I typically plan on doing is set this as a git submodule, and bring it into a project and import the module using something like:

from pycrtm.pyCRTM import profilesCreate, pyCRTM

Or, do something like is done in the testCases scripts and insert the path, then import.

pycrtmDir = [this directory]
sys.path.insert(0,pycrtmDir)
from pyCRTM import pyCRTM, profilesCreate

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4. Using the interface (designed to be pretty much like the RTTOV equivalent python library):

Create a profiles data structure using profilesCreate(nprofiles, nlayers) which will generate an object with user specified number of profiles, and number of layers in the profiles provided.

profiles = profilesCreate(4, 92) # will generate an empty object with 4 profiles each with 92 layers. 

Once initialized, the user will need to provide values for the desired profiles (see example scripts). Next, the user initializes a crtm instance, set desired parameters, and passes profiles to the CRTM:

crtmOb = pyCRTM()
crtmOb.coefficientPath = pathInfo['CRTM']['coeffs_dir']
crtmOb.sensor_id = sensor_id
crtmOb.nThreads = 4
crtmOb.profiles = profiles

Next, the instrument is loaded/number of channels in the output structure are initialized:

crtmOb.loadInst()

Next, the user can run either the forward model (runDirect), or the K-matrix (runK)

crtmOb.runDirect()
crtmOb.runK()

Finally, the user can pull out desired parameters such as brightness temperatures, Jacobians, or Transmission along path (TauLevels - the derivative will be the weighting function):

# brightness temperature (nprofiles, nchan):
brightnessTemperature = crtmOb.Bt 

#Transmission (to compute weighting functions) ( nprofiles, nchan, nlayers)
Tau = crtmOb.TauLevels 

#Temperature, Water Vapo[u]r, and Ozone Jacobians ( npforfiles, nchan, nlayers)
O3_Jacobian = crtmOb.O3K
Water_Vapor_Jacobian = crtmOb.QK
Temperature_Jacobian = crtm.TK

#Emissivity (nprofiles, nchan)
Emissivity = crtmOb.surfEmisRefl

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