
VLIDORT History In 2004, the vector code VLIDORT for light scattering with polarization was created for Stokes 3 and 4vector output. The pseudospherical approximation was used from the output, with particular integrals established using the classical (Chandrasekhar) exponential substitution method. Profile linearization was completed in 2005. In 2006, VLIDORT was given the bulkproperty linearization, and the reflectionmatrix BRDF surface capability was installed; thermal emission and accurate singlescatter calculations were introduced in 2007 (Version 2.0). The capabilities for VLIDORT were then brought up to the same level as those for the scalar code LIDORT; this effort culminated in Version 2.4 (2009). In recent years, the VLIDORT code has been upgraded to Fortran 90 (2011, Version 2.5), and the surfaceleaving, external SS and observational geometry options introduced (2013, Version 2.6). In 2015, the code was made threadsafe for use in parallelcomputing environments. Recent developments with the LIDORT code have also been installed in VLIDORT. These include the "planetary problem" facility, temperature (Planck function) Jacobians for thermal sources, and the use of the multiplescattering sphericity correction. In addition, VLIDORT has an alternative treatment of the 3vector (linear polarization) radiative transfer equation using the Greek's function method. VLIDORT is currently at Version 2.8.3.
VLIDORT Capabilities Similar to LIDORT 3.8.3, VLIDORT Version 2.8.3 is a multiplescattering multilayer discrete ordinate scattering code with a simultaneous linearization facility for the generation of both radiances and analytic Jacobians (intensity partial derivatives with respect to any atmospheric or surface parameter). The model will generate upwelling and/or downwelling output for any number of geometrical configurations and at any atmospheric level. Linearization is available for atmospheric profile Jacobians or atmospheric bulkproperty Jacobians such as total column amounts, as well as for surface properties. However, unlike LIDORT, VLIDORT can generate output for the entire Stokes vector [I, Q, U, V]. The option to output the Stokes 3vector linearly polarized field (V component absent) also exists. Neglecting polarization altogether in VLIDORT gives identical results to those calculated with LIDORT. As with LIDORT, VLIDORT is a pure scattering RT model; it ingests total optical properties appropriate for doing vector calculations: layer optical depths, single scattering albedos, the 4x4 phase matrix of expansion coefficients appropriate for scatteringmatrix expansions in terms of generalized spherical functions, and total surface properties. It does not distinguish individual atmospheric absorbers and scatterers, and (for surface BRDFs) the type of surface. VLIDORT treats multiple scattering in planeparallel geometry, but for the single scattering (FO) field, solar and lineofsight beams may be computed more accurately for curved spherical media. VLIDORT has a complete blackbody atmospheric and surface thermal emission treatment; a full linearization capability is installed for thermal sources  this includes temperature Jacobians through the use of Planck function derivatives. In VLIDORT, particular integral RTE solutions have always been obtained using classical (Chandrasekhar) substitution methods for dealing with sets of coupled linear differential equations. However, now there is an alternative for VLIDORT  it can also operate using the infinitemedium Green's function method to solve the RTE (for linear polarization only). VLIDORT also has the same four supplements:
VLIDORT also has a number of performance enhancements:
VLIDORT is available in Fortran 90 (Version 2.8.3) and Fortran 77 (version 2.5).



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