Considering polarization in MODIS-based cloud property retrievals by using a vector radiative transfer code

- Impact of polarization on satellite-based retrieval of water/ice cloud properties is studied.
- Inclusion of polarization can change water/ice optical thickness and effective diameter values by up to ±15%.
- Influence of polarization on cloud property retrievals depends on sun-satellite viewing geometries.

In this study, a full-vector, adding-doubling radiative transfer model is used to investigate the influence of the polarization state on cloud property retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. Two sets of lookup tables (LUTs) are developed for the retrieval purposes, both of which provide water cloud and ice cloud reflectivity functions at two wavelengths in various sun-satellite viewing geometries. However, only one of the LUTs considers polarization. The MODIS reflectivity observations at 0.65 μm (band 1) and 2.13 μm (band 7) are used to infer the cloud optical thickness and particle effective diameter, respectively. Results indicate that the retrievals for both water cloud and ice cloud show considerable sensitivity to polarization. The retrieved water and ice cloud effective diameter and optical thickness differences can vary by as much as ±15% due to polarization state considerations. In particular, the polarization state has more influence on completely smooth ice particles than on severely roughened ice particles.