Retrieval of aerosol properties from HARP observations

Abstract:

Aerosols play an important role in the Earth’s radiation budget and possess a hazard to human health. MAPs (Multi-Angle Polarimeters) have the potential to retrieve aerosol properties with higher accuracy than traditional imaging radiometers. HARP (Hyper-Angular Rainbow Polarimeter) is a standalone CubeSat launched from the ISS in February 2020 and has the hyper-angular imaging capability of 60 viewing angles at 670 nm, 10 viewing angles at 870 nm and 9 viewing angles at other wavelengths 440 nm, 550 nm across the full 114° (94°) along-track (cross-track) field-of-view. HARP can measure I, Q, U elements of the Stokes vector at all four wavelengths. On-orbit vicarious radiometric and polarimetric calibration are done using the collocated observations from the NASA and NOAA satellite remote sensing instruments MODIS, VIIRS, and ABI. The aerosol properties are retrieved using the inversion of HARP measurements with the GRASP (Generalized Retrieval of Aerosols and Surface Properties) algorithm. GRASP is an open source versatile algorithm to retrieve aerosols and surface properties using various ground-based and satellite remote sensing observations. Here we report the preliminary on-orbit vicarious calibration technique used and the retrieved aerosol properties like AOD (Aerosol Optical Depth), AE (Angstrom Exponent), SSA (Single Scattering Albedo), fine and coarse mode AOD, and information on the size and shape of the particles. These results will give insight on what MAPs can offer to future Earth observing missions like NASA PACE (Phytoplankton, Aerosol, Cloud and ocean Ecosystem) and ACCP (Aerosol and Cloud, Convection and Precipitation).