Retrievals of marine liquid water cloud microphysical properties from OCO-2 observations

Abstract:

The Orbiting Carbon Observatory-2 has been collecting high spectral resolution radiance measurements in the NASA A-Train orbit since 2014. The primary application of these spectral measurements is retrieval of the total column carbon dioxide mole fraction, but the measurements contain additional information on cloud properties. The three OCO-2 spectral bands (0.77, 1.6, and 2.1 μm wavelength) are comparable to the MODIS bands used for retrievals of cloud droplet effective size and optical thickness (bands 2, 6, and 7 at 0.8, 1.6 and 2.1 μm, respectively). The high spectral resolution of the OCO-2 measurements allows additional investigation into sensitivity of the retrievals to model assumptions such as cloud homogeneity or droplet size distribution shape. We report results of a Look Up Table (LUT) based retrieval applied to the OCO-2 data to estimate particle effective radius and optical thickness of marine liquid water clouds. These results are compared to co-located retrievals from MODIS-Aqua. Analysis of spectral residuals and sensitivity studies using the OCO-2 forward model are used to investigate the impacts of different model assumptions.