Introduction to the LIDORT Family of Products

In the last thirty years, there has been increasing recognition of the need for radiative transfer models (RTMs) not only to produce simulated radiation fields but also to generate simultaneous fields of analytic derivatives (Jacobians) with respect to atmospheric and surface variables. Such models are extremely useful in classic inverse-problem retrievals involving some kind of iterative least-squares minimization (with and without regularization). An RTM with this dual ability is often said to possess the linearization capacity. A number of "linearized" RTMs have emerged in the last 20 years, and this includes the LIDORT (LInearized Discrete Ordinate Radiative Transfer) model first developed by Robert Spurr, the Director of RT Solutions, in 1999.

LIDORT is a scalar model (no polarization). However, the treatment of polarization is critical for the successful retrieval of ozone profiles from UV backscatter for example, and the use of passive sensing instruments with polarization capabilities can greatly enhance retrievals of aerosol information in the atmosphere. The vector VLIDORT model addresses the radiative transfer of polarized light, and it too has a full linearization capability. RT Solutions also has other radiative transfer models. These include a scalar code with first-order inelastic rotational Raman scattering by air molecules; this code is called LRRS (LIDORT-RRS), and it too has the linearization capability. More recently, a newer VLIDORT-style code has been developed to handle nadir- and limb-viewing scenarios in a spherically curved atmosphere; this is the VLIDORT-QS (Quasi-Spherical) code, which also has a Jacobian facility. These products are listed below.