Potential of NASA’s Plankton, Aerosol, Cloud, and Ocean Ecosystem (PACE) Satellite Observations in the Oxygen Bands for Determining Aerosol Layer Height over Ocean

Abstract

Aerosol layer height (ALH) is an important but uncertain parameter for evaluating the impact of aerosols on weather and climate and for accurate atmospheric correction. This study aims to assess the potential for measuring ALH by the Ocean Color Instrument (OCI) on NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem satellite. OCI measures Earth-reflected solar spectrum including reflectance in the oxygen (O2) A and B absorption bands that are invaluable for determining ALH. We assessed the sensitivity and information contained therein in retrieving ALH over the ocean surface by using the radiative transfer simulation of OCI observations in the O2 bands. The capabilities were also demonstrated using hyperspectral data measured by the TROPOspheric Monitoring Instrument (TROPOMI), as spectrally convolved into the OCI bands. Our results indicate that (a) OCI observations in the O2 A band are sensitive to ALH, whereas those around the O2 B band have relatively reduced sensitivity; (b) the most pronounced sensitivity to ALH is found in the 762.5 nm (and 690 nm) around the oxygen A (and B) bands, which are selected for ALH retrievals in this study; and (c) the ALH retrieved from OCI proxy data is in good agreement with the aerosol profile probed by CALIOP lidar. Overall, the ALH retrievals for both smoke and dust events exhibit a root mean square error of 0.49 km and 0.31 km, respectively, for the smoke and dust cases, aligning with the uncertainties of ALH as measured from the concurrent TROPOMI and the Earth Polychromatic Imaging Camera instruments. Therefore, this study suggests from OCI observations that we can generate ALH products with a well-characterized uncertainty. The technique and results presented in this study are suitable to develop a simple but robust ALH algorithm for OCI observations when the data become available.