Progress of Community Radiative Transfer Model (CRTM) Development

The CRTM is a fast model to calculate satellite observed radiance and its sensitivity to atmospheric and surface state variables in UV, VIS, IR and MW spectral regions. It is widely used as an observation operator for radiance data assimilation, satellite-based retrieval system, remote sensing algorithm development and for cal/val applications in the community. In CRTM, atmospheric gas absorption is calculated in sensor-channel base using regressing methods fitting to line-by-line calculations. Scattering radiative transfer (RT) is calculated with Advanced Doubling‐Adding (ADA) algorithm. It also includes a comprehensive set of models for surface emissivity and reflectivity over land, ocean, ice and snow surfaces. Correction algorithms are implemented for the Non-Local Thermodynamic Equilibrium (NLTE) effects and Zeeman-splitting effect. The tangent-linear and adjoint/K-matrix are implemented with an algorithm differentiation method.

In this presentation developments and activities in progress will be reported. New developments in CRTM include extension of ADA to full Stokes polarization calculation; support for new sensors from JPSS-2 (now NOAA-21), GOES-18, 19, MetOp-SG, MTG, GeoXO, and those on the future SmallSats. New observations from active sensors and UV instruments are also added. To support all-sky data assimilation, in development is a new cloud database that upgrades the ice phase hydrometeor scattering calculation and supports polarization RT and active sensor simulations. The CRTM transmittance coefficient generation package is largely updated with streamlined and automated workflow.

The CRTM is a fast model to calculate satellite observed radiance and its sensitivity to atmospheric and surface state variables in UV, VIS, IR and MW spectral regions. It is widely used as an observation operator for radiance data assimilation, satellite-based retrieval system, remote sensing algorithm development and for cal/val applications in the community. In CRTM, atmospheric gas absorption is calculated in sensor-channel base using regressing methods fitting to line-by-line calculations. Scattering radiative transfer (RT) is calculated with Advanced Doubling‐Adding (ADA) algorithm. It also includes a comprehensive set of models for surface emissivity and reflectivity over land, ocean, ice and snow surfaces. Correction algorithms are implemented for the Non-Local Thermodynamic Equilibrium (NLTE) effects and Zeeman-splitting effect. The tangent-linear and adjoint/K-matrix are implemented with an algorithm differentiation method.

In this presentation developments and activities in progress will be reported. New developments in CRTM include extension of ADA to full Stokes polarization calculation; support for new sensors from JPSS-2 (now NOAA-21), GOES-18, 19, MetOp-SG, MTG, GeoXO, and those on the future SmallSats. New observations from active sensors and UV instruments are also added. To support all-sky data assimilation, in development is a new cloud database that upgrades the ice phase hydrometeor scattering calculation and supports polarization RT and active sensor simulations. The CRTM transmittance coefficient generation package is largely updated with streamlined and automated workflow.