IPRT polarized radiative transfer model intercomparison project – Phase A

Abstract

a b s t r a c tThe polarization state of electromagnetic radiation scattered by atmospheric particles such as aerosols, cloud droplets, or ice crystals contains much more information about the optical and microphysical properties than the total intensity alone. For this reason an increasing number of polarimetric observations are performed from space, from the ground and from aircraft. Polarized radiative transfer models are required to interpret and analyse these measurements and to develop retrieval algorithms exploiting polarimetric observations. In the last years a large number of new codes have been developed, mostly for specific applications. Benchmark results are available for specific cases, but not for more sophisticated scenarios including polarized surface reflection and multi-layer atmospheres. The International Polarized Radiative Transfer (IPRT) working group of the International Radiation Commission (IRC) has initiated a model intercomparison project in order to fill this gap. This paper presents the results of the first phase A of the IPRT project which includes ten test cases, from simple setups with only one layer and Rayleigh scattering to rather sophisticated setups with a cloud embedded in a standard atmosphere above an ocean surface. All scenarios in the first phase A of the intercomparison project are for a one-dimensional plane-parallel model geometry. The commonly established benchmark results are available at the IPRT website

Errors induced by the neglect of polarization in radiance calculations for three-dimensional cloudy atmospheres

“…MYSTIC has participated in various model intercomparison studies [33,34,35,36] and always agreed perfectly to commonly established benchmark results.…”

IPRT polarized radiative transfer model intercomparison project – Three-dimensional test cases (phase B)

“…Some systematic deviations are found for the only deterministic code SHDOM: for case 2, where the sensor looks exactly into zenith direction, we see rather large deviations for Stokes component Q. The IPRT 1D intercomparison (Emde et al, 2015) showed a problem SHDOM has for Stokes components Q and U near θ=0 • and θ=180 • for highly peaked phase functions, and this issue has not yet been resolved. Figure 4 shows the results for down-looking geometries (test cases 5-9), where the observer is placed at the top of the cloud layer at position x looking downwards.…”

The libRadtran software package for radiative transfer calculations (version 2.0.1)

“…Polarized radiative transfer using MYSTIC has been validated in extensive model intercomparison projects (Kokhanovsky et al, 2010a;Emde et al, 2015). Figure 10 shows an example for simulations at wavelengths of 443, 670, and 865 nm; these are measured by the POLDER (Polarization and Directionality of the Earth's Reflectances) instrument onboard PARASOL (Deschamps et al, 1994) The first row shows the results for a clear atmosphere, i.e.…”