The I3RC project was initiated by Robert Cahalan in the mid 1990s, with funding from the Department of Energy Atmospheric Radiation Measurement Program and the NASA Radiation Sciences Program, and with endorsements from International Radiation Commission and GEWEX Radiation Panel. Its goals include:
Assessing MODIS MBL cloud retrieval using Large-Eddy Simulation and 3D RT model
Marine Boundary Layer (MBL) clouds are thought to be at the heart of cloud feedback uncertainties in climate models. How and to what extent man-made aerosols may affect the properties of MBL clouds is poorly understood. Measures to address these issues rely heavily on satellite-based remote sensing of the microphysical and optical properties of these clouds. The image shows recent research activities by branch scientists of assessing how the 3D cloud structure (i.e., cloud top entrainment, cloud particle size vertical variation and drizzle) and 3D radiative effects influence MODIS MBL cloud retrieval. MODIS (or Moderate Resolution Imaging Spectroradiometer) is a key instrument aboard the Terra (EOS AM) and Aqua (EOS PM) satellites. The upper panel shows the cloud optical thickness simulated from a Large-Eddy Simulation (LES) model (Stevens et al. 1998 JAS). The middle panel shows the differences in the upwelling radiances at three wavelengths used for MODIS cloud retrieval at nadir between 3D (simulated using I3RC) and 1D (simulate using DISORT) radiative transfer simulations. The solar zenith and azimuth are 60° and 0° (x+ direction), respectively. In 3.7 um simulation, only the solar reflectance component is considered (i.e., assuming the thermal component is perfectly corrected by the atmospheric correction step in MODIS retrieval). MODIS cloud effective radius retrievals based on simulated radiances are shown in the lower panel. Note that in the shadowing region(for example around 4km), the cloud appears darker in the 3D simulation than the 1D simulation due to the shadowing effect As a result, the effective radius retrievals based on 3D radiance are larger in these regions. This research will help scientists to better understand how cloud structure and 3D radiative effects influence satellite retrieval data.
Zhibo Zhang and Steven Platnick