Retrieval and validation of aerosol and surface properties from HARP2/PACE using GRASP algorithm

NASA's Plankton, Aerosol, Clouds, and ocean Ecosystem (PACE) mission was successfully launched on February 8, 2024. A key instrument aboard the PACE platform- the Hyper-angular Rainbow Polarimeter-2 (HARP2), a state-of-the-art multi-angular polarimeter, collects data from multiple viewing angles spanning -54.5° to +54.5° across 4 channels ranging from visible to near-infrared wavelengths, with measurements of linear polarization at three directions. Thus, HARP2 has very high sensitivity to aerosol characteristics, including particle size, type, and absorption etc.

In this study, the Generalized Retrieval of Aerosol and Surface Properties (GRASP) algorithm was utilized to retrieve aerosol and surface parameters simultaneously from HARP2 measurements collected over the past half year. Validation of aerosol properties was conducted by comparing HARP2/GRASP products with ground-based AERONET observations, while surface property retrievals were evaluated against MODIS surface products. The results have demonstrated encouraging performance: spectral AOD shows a high correlation with AERONET data with correlation coefficients ~0.9and a mean bias of -0.01. The Ångström Exponent (AE) and single scattering albedo (SSA), also showed reasonable agreement, with AE and SSA achieving correlation coefficients of 0.54 and 0.9. Surface property retrievals exhibited robust correlations with MODIS data, demonstrating the effective decoupling of surface and atmospheric signals from the satellite observations.

This research highlights the potential of HARP2/GRASP products in providing accurate aerosol and surface parameters, leveraging HARP2’s polarimetric capabilities. In the future, we will also explore the synergistic potential of integrating observations from multiple PACE instruments to enhance the information content and improve retrieval coverage and accuracy.