Cloud and Aerosol Imager Retrievals during ORACLES 2016: Evaluation of Cloud Microphysics and Above-Cloud Aerosol Optical Property Retrievals

The 2016 deployment of the NASA ObseRvations of CLouds above Aerosols and their intEractionS (ORACLES) field campaign included wide swath, high spatial resolution imagery from the Enhanced MODIS Airborne Simulator (eMAS) flown onboard the ER-2 high altitude research aircraft. eMAS, with a 37km wide swath and 50m spatial resolution from a 20km flight altitude, measures reflected solar and emitted terrestrial radiation at 38 narrowband channels covering the 0.47 – 14µm spectral range. The eMAS cloud retrieval science that supported ORACLES includes cloud products sharing heritage with the space-borne MODIS operational cloud product MOD06. Here we present first results of an evaluation of eMAS retrievals of the southeast Atlantic marine boundary layer stratocumulus cloud microphysics (i.e., cloud effective droplet radius, CER) in the ORACLES region using co-located in situ droplet size observations from the Phase Doppler Interferometer (PDI) flown on the P-3 and polarimetric remote sensing retrievals from the Research Scanning Polarimeter (RSP) also on the ER-2. In addition to eMAS CER retrievals using the shortwave infrared channels analogous to MODIS (1.6, 2.1, 3.7µm), retrievals from alternate channels within the broader 1.6 and 2.1µm spectral regions will be considered as well (including a VIIRS-like 2.23µm channel). Evaluation results will be informed by droplet size distribution widths (effective variance) observed by PDI and inferred from RSP; size distribution effective variance is a key cloud forward model assumption for passive imager microphysical retrievals. Finally, we will also briefly present first results of the MOD06ACAERO algorithm applied to eMAS; this at present research-level algorithm provides simultaneous retrievals of above-cloud absorbing aerosol and the unbiased underlying cloud optical thickness and effective particle size from reflectances at multiple spectral channels in the visible, near-infrared, and shortwave infrared spectra.