Choosing an Engine¶
SASKTRAN is a framework containing modules to handle all aspects of the radiative transfer problem, including setting up the geometry, defining the atmosphere, and solving the radiative transfer equation. The radiative transfer equation can be solved in multiple ways, and SASKTRAN contains multiple engines, or solvers, to perform this task. Which engine to use depends on the specific task at hand.
SASKTRAN-HR is the primary engine used and is described in Zawada et. al. (2015). SASKTRAN-HR is contained within the primary SASKTRAN package.
Problems requiring fast and accurate radiative transfer in the UV-VIS-NIR spectral region where scattering is dominant.
Fully spherical geometry
Approximate, analytic Jacobian calculation
Support for two- and three-dimensionally varying atmospheres
Accuracy is controlled by a wide variety of settings which may require specific tuning for your problem.
Support for atmospheric emissions is available, but experimental and limited.
SASKTRAN-OCC is an engine designed for fast occultation applications. SASKTRAN-OCC is contained within the primary SASKTRAN package.
Occultation viewing geometry in all spectral regions.
Refraction is treated within a fully spherical atmosphere
Scattering and emission terms are neglected
SASKTRAN-MC performs Monte-Carlo integration to solve the RTE and is described in Zawada et. al. (2015). SASKTRAN-MC is contained within the main SASKTRAN package.
Problems requiring accurate radiative transfer in the UV-VIS-NIR spectral region where scattering is dominant and runtime is of secondary concern.
Fully spherical geometry
Accurate, requiring much less configuration than SASKTRAN-HR
Can be slow depending on the application
Results contain random noise
SASKTRAN-DO is a discrete ordinates solver based upon the Lidort technique. SASKTRAN-DO must be installed separately and can be found at https://arg.usask.ca/docs/sasktran_do/
Nadir viewing applications in the UV-VIS-NIR spectral region.
Perfectly linearized for most inputs
Not suitable for limb viewing applications
Errors that increase as the viewing zenith angle increases.
SASKTRAN-TIR is a thermal radiative transfer model designed for applications in the IR and beyond spectral regions. SASKTRAN-TIR must be installed separately and can be found at https://arg.usask.ca/docs/sasktran_tir/.
Applications in the IR and beyong spectral regime where scattering can be neglected.
Linearized for most atmospheric parameters
Scattering is not included
Zawada, D. J., Dueck, S. R., Rieger, L. A., Bourassa, A. E., Lloyd, N. D., and Degenstein, D. A.: High-resolution and Monte Carlo additions to the SASKTRAN radiative transfer model, Atmos. Meas. Tech., 8, 2609-2623, https://doi.org/10.5194/amt-8-2609-2015, 2015.
Bourassa, A. E., Degenstein, D. A., and Llewellyn, E. J.: SASKTRAN: A Spherical Geometry Radiative Transfer Code for Efficient Estimation of Limb Scattered Sunlight, J Quant Spectrosc Radiat Trans, Volume 109, Issue 1, 52-73, https://doi.org/10.1016/j.jqsrt.2007.07.007, 2008.