Observing System Simulation Experiment for a Multi-Angle Polarimeter

The 2017-2027 Decadal Survey for Earth Science and Applications from Space (ESAS 2017) identifies aerosols as a high priority Earth observation needed over the next decade. A mission study for this so-called designated observable has been developed to identify candidate instrument concepts that can further our knowledge of the role aerosols play in the Earth system. One such notional instrument is a multi-angle polarimeter, such as the Hyper-Angular Rainbow Polarimeter (HARP), but with extended observing capability in the UV and/or SWIR. In this presentation, we will show results of applying the Generalized Retrieval of Aerosol and Surface Properties (GRASP) retrieval algorithm to synthetic observations of a HARP-like instrument. The synthetic observations were created using the Goddard instrument simulator that is based on output from a global mesoscale (approximately 7 km horizontal resolution) simulation with the Goddard Earth Observing System (GEOS) model that includes a comprehensive aerosol modeling package. GEOS provides high-time frequency, global three-dimensional distributions of meteorology, clouds, and speciated aerosols. Sub-sampled GEOS output and associated instrument viewing geometries are inputs to the Goddard instrument simulator, which uses a vector radiative transfer (RT) code to compute top-of-atmosphere multi-spectral, multi-angular polarized reflectance as would be observed by a satellite. The retrievals performed on the synthetic observations are compared to the known model inputs to the RT code (i.e. the "ground truth") in order to assess the capabilities of the existing GRASP algorithm to retrieve aerosol physical and optical properties from observations from a HARP-like polarimeter.