LIDORT-RRS History

The inelastic rotational Raman scattering code LIDORT-RRS was developed initially in 2003-2005 (Versions 1.0 to 1.5). The code has two realizations ("Binning" and "Monochromatic") for dealing with Raman-scattered contributions. LIDORT-RRS was extended in 2006-2007 to include BRDF surfaces, exact single scatter calculations and output at any level in the atmosphere (Version 2.1). The LIDORT-RRS code was translated to Fortran 90 in 2010, and given a full profile/column Jacobian linearization in 2011 (Version 2.3) Surface-leaving and external SS options were introduced in 2012. In line with recent upgrades to LIDORT and VLIDORT, LRRS now has a complete set of supplements for BRDFs, surface-leaving and single-scatter results that are completely compatible with the LIDORT supplements. LRRS has also been given thread-safe capabilities, both externally for calculations in the monochromatic mode, and internally for binning-mode calculations. LRRS is currently at Version 2.5a.

LIDORT-RRS Capabilities

LIDORT-RRS Version 2.5a is a multiple-scattering multi-layer discrete ordinate scattering code which includes elastic and inelastic (rotational-Raman) scattering. The inelastic scattering is first-order (photons are only Raman scattered once). Raman cross-sections are either grouped according to the wavelength resolution of the input solar spectrum (the "binning realization") or treated individually (the "monochromatic realization", slower). The model will generate upwelling and/or down-welling output for any number of geometrical configurations and at any atmospheric layer boundary.

LIDORT-RRS has a simultaneous linearization facility for the generation of both radiances and analytic Jacobians (intensity partial derivatives with respect to any atmospheric or surface parameter). Linearization is available for atmospheric profile Jacobians or atmospheric bulk-property Jacobians such as total column amounts, as well as for surface properties.

LIDORT-RRS is a scattering RT model; it ingests "elastic" total optical properties (layer optical depths, single scattering albedos and phase-function Legendre expansion coefficients) and their linearizations. It also ingests layer temperatures, air-column densities and Rayleigh cross-sections - these are required for the internal computation of Raman-scattering optical properties. [Raman spectroscopy data is included in the model].

LIDORT-RRS treats multiple scattering in plane-parallel geometry, but for the single scattering field, solar and line-of-sight beams may be computed more accurately for curved spherical media (pseudo-spherical approximation).

LIDORT-RRS uses the substitution method to solve for the unperturbed elastic field RTE, and the Green's function method for solving the layer RTEs with additional inelastic source terms.

LIDORT-RRS currently has two supplements:

1. the BRDF supplement is based on surface reflection kernels (semi-empirical reflectance functions developed for particular types of surfaces) and provides the total BRDFs required for LIDORT-RRS to execute; this includes full surface property linearizations;
2. the SL (surface-leaving) supplement provides surface-leaving radiance sources (currently restricted to water-leaving or solar-induced fluorescence).

LIDORT-RRS also has some performance enhancements:

1. the delta-M scaling approximation for sharply-peaked phase functions;
2. the code is "thread-safe", in that is can be used in parallel-computing environments such as OpenMP.

NOTE: There is a vector version of the LRRS code, called VLRRS, which has been developed recently (2021), and is currently undergoing final testing. VLRRS has all the capabilities of the scalar LRRS code mentioned above. VLRRS works with Stokes 3-vectors (linearized polarization) and reproduces exactly the output from LRRS when running in scalar mode without polarization.