kCARTA: A fast pseudo line-by-line radiative transfer algorithmwith analytic Jacobians, fluxes, Non-Local ThermodynamicEquilibrium and scattering for the infrared

Abstract. A fast pseudo-monochromatic radiative transfer package using a Singular Value Decomposition (SVD) compressed atmospheric optical depth database has been developed, primarily for use with hyperspectral sounding instruments. The package has been tested extensively for clear sky radiative transfer cases, using field campaign data and satellite instrument data. The current database uses HITRAN 2016 line parameters and is primed for use in the spectral region spanning 605 cm−1 to 2830 cm−1 (with a point spacing of 0.0025 cm−1), but can easily be extended to other regions. The clear sky radiative transfer model computes the background thermal radiation quickly and accurately using a layer-varying diffusivity angle at each spectral point; it takes less than 20 seconds (on a 2.8 GHz core using 4 threads) to complete a radiance calculation spanning the infrared. The code can also compute Non Local Thermodynamic Equilibrium effects for the 4 μm CO2 region, as well as analytic temperature, gas and surface jacobians. The package also includes flux and heating rate calculations, and an interface to a scattering model.