LIDORT History

The original LIDORT code (Version 1.0) developed in 1999 generated radiance and profile- Jacobian output for top-of-atmosphere (TOA) reflectances in a plane-parallel multi-layer atmosphere. In 2000/2001, the model was generalized to include a pseudo-spherical treatment of solar beam attenuation, output at arbitrary optical thickness and viewing geometry, and the use of Green's function solution methods (Versions 2.1-2.3). A dedicated "sphericity correction" to deal with simulations involving wide-angle off-nadir viewing was introduced in 2002. In 2003, a second linearization facility for bulk-atmospheric quantities (such as total ozone column) was introduced. In 2004 LIDORT Version 2.4 was developed for a detailed treatment of BRDFs and surface property Jacobians. Thermal and surface emission was introduced to LIDORT in 2007, including the Jacobian facility. These developments culminated in Version 3.3 (2008). In recent years, the emphasis has been on upgrading the LIDORT code and improving performance; in 2010, the code was translated to Fortran 90 (Version 3.5). In 2012, a surface-leaving radiance source was introduced, along with the ability to ingest external single scatter (SS) radiance fields, and a facility for generating output at observational geometries only (Version 3.6). In 2014, additional linearization was added for temperature Jacobians in the thermal regime, and the code was made thread-safe for use in OpenMP environments. More recently, Supplements for BRDF and (in particular) surface-leaving radiances were given extensive upgrades, and the single-scatter codes completely revised. LIDORT is currently at Version 3.8 (Fortran 90).


LIDORT Capabilities

LIDORT Version 3.8 is a multiple-scattering multi-layer 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 down-welling output for any number of geometrical configurations and at any atmospheric level. Linearization is available for atmospheric profile Jacobians or atmospheric bulk-property Jacobians such as total column amounts, as well as for surface properties.

LIDORT is a pure scattering RT model; it ingests total optical properties (layer optical depths, single scattering albedos and phase-function Legendre expansion coefficients) and their linearizations, and total surface properties. It does not distinguish individual atmospheric absorbers and scatterers, and (for surface BRDFs) the type of surface.

LIDORT 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). This "enhanced sphericity" treatment is suitable for important satellite applications involving wide off-nadir viewing geometry, and horizontal variations in the line-of-sight direction.

LIDORT has a complete black-body 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.

LIDORT uses the Green's function method for solving the layer radiative transfer equations (RTEs), both for solar and thermal-emission sources.

LIDORT has four supplements: (1) the BRDF supplement is kernel-based (semi-empirical reflectance functions developed for particular types of surfaces) and provides total BRDFs required for LIDORT 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); (3) the SS (single-scatter) supplement holds the external first-order fields if these are to be ingested by LIDORT as an alternative to an internal calculation of these fields; (4) a new supplement for generating phase-function inputs to be used directly in single-scatter calculations.

LIDORT has a number of performance enhancements: (1) the delta-M scaling approxi-mation for sharply-peaked phase functions; (2) "solution-saving" and "boundary-value telescoping" options to avoid unnecessary computation for situations with contiguous cloud or aerosol layers embedded in a Rayleigh atmosphere; (3) the option to ingest "observational geometry" angular input, in order to save time on post-processing; and (4) thread-safe code that can be used in parallel computing environments such as OpenMP.

LIDORT is available in Fortran 90 (Version 3.8) and Fortran 77 (version 3.5).




© RT Solutions, Inc. (2006) :: website created by Christine Imrey
© RT Solutions, Inc. (2013,2017,2019) :: website updated by Matt Christi

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