VLIDORT User's Guide

and a complete differentiation of the BRDF formulation was developed to generate Jacobianswith respect to surface variables such as the wind speed.Support for maintaining LIDORT Versions 1 and 2 came from a series of contracts over theperiod 1999-2004 which provided the sources of funding for R. Spurr while at SAO. Inrecognition of the need for a consistent set of supported RT codes for use at NASA-GSFC, acontract was set up between SSAI Inc. and RT Solutions Inc. for the developmental release ofLIDORT Versions 3.0 and beyond; all subsequent User Guides were written under this aegis.From Version 3.0 onwards, all previous LIDORT codes are integrated. The last of the olderversions to be incorporated was Version 2.5; this had the specialist ability for fast generation oftotal column (as opposed to profile) Jacobians, and this capability was integrated into LIDORT3.3 in May 2007. New features for Versions 1.0 to 3.3 are (1) a Green’s function treatment of theRTE with atmospheric thermal emission; (2); a new outgoing sphericity correction that replacesthe old treatment of single scatter along the line-of-sight path; (3) the inclusion of a bulk property(total column) weighting function treatment. A number of other improvements were added,including a stand-alone facility for returning the single scatter radiance and Jacobians, anadditional scaling procedure for the single scatter RTE, and an internal adjustment to utilizegeometrical variables at any height in the atmosphere.1.2.2. VLIDORT Development, Versions 1.0 to 2.4In December 2003, a proposal was made to FMI for R. Spurr to develop the vector modelVLIDORT as part of the O3SAF Visiting Scientist (VS) program in 2004. The first version ofVLIDORT was completed in July 2004, given shakedown tests and validated against theCoulson/Dave/Sekera Rayleigh results [Coulson et al., 1960] and Siewert’s [Siewert, 2000b]benchmark results. The first application started in August 2004 with polarization sensitivitystudies on the UV product algorithm at FMI, and the Version 1.0 User’s guide appeared inSeptember 2004.In January 2005, a proposal was made and accepted for the continuation of VLIDORT studies aspart of the Ozone SAF Visiting Scientist Work in 2005. A number of VLIDORT improvements(refractive geometry, single scatter corrections, and performance enhancements) were made inspring 2005, and this was followed by an end-to-end linearization of the code, so that the newversion of VLIDORT now possessed a complete weighting-function capability. This December2005 version marked the completion of the initial VLIDORT development [Spurr, 2006] Afurther validation against the benchmark results of [Garcia and Siewert, 1989] was performed atthis time.Support for VLIDORT maintenance and development from 2006 has come from an RTSolutions’ contract with SSAI and NASA GSFC. The first new development for LIDORT andVLIDORT was the introduction of a new and more accurate single scatter scheme to allow forspherical geometry along the view path as well as the solar paths. The model has been usedextensively at NASA GSFC in OMI-related studies, and in spring 2007, it was carefullyvalidated against the older TOMRAD code at GSFC.For VLIDORT version 2.4R, the linearization facility was extended to include column or bulkproperty Jacobians, a facility that was introduced into the scalar LIDORT code in 2003. Inaddition to the new bulk Jacobian facility, version 2.4R also contains some new BRDFspecifications for polarized reflectance from land surfaces. Thermal emission was introducedinto this version of the code.10