Aerosol Validation in NASA's PACE mission: Deployment of the SPEX Airborne Polarimeter in the PACE-PAX Field campaign

The Plankton, Aerosol, Cloud, Ocean Ecosystem Postlaunch Airborne eXperiment (PACE-PAX) is a multi-platform, multi-instrument field campaign designed to validate NASA’s PACE mission. Two research aircraft participated in this month-long campaign: the CIRPAS Twin Otter, conducting in situ observations of aerosols and clouds, and NASA’s high-altitude research aircraft ER-2, equipped with remote sensing instruments. Among these instruments is SPEX airborne, an airborne proxy for the Dutch SPEXone instrument onboard PACE. SPEX airborne, like SPEXone, is a multi-angle spectropolarimeter for wavelengths between 400 and 780 nm, designed to characterize aerosols in the Earth’s atmosphere. It has nine viewing angles (nadir, ±14°, ±28°, ±42°, and ±56°) and an across-track swath of about 2.1 km at nadir at nominal ER-2 flight altitudes. SPEX airborne radiance and polarization data are formatted identically to SPEXone data, enabling the use of the same RemoTAP algorithm to retrieve aerosol properties such as aerosol optical depth, size distributions, refractive index, layer height, and composition. During multiple flights, totaling over 80 flight hours, the ER-2 frequently flew under PACE and ESA’s EarthCARE satellite, as well as over the Twin Otter, calibration sites, and aerosol ground stations, facilitating extensive data comparisons. In this presentation, we present preliminary validation of publicly released SPEX airborne level-1 data and collocate these with SPEXone observations. Additionally, we present validation of SPEX airborne aerosol retrievals against AERONET stations and other instruments deployed during PACE-PAX. The RemoTAP aerosol retrievals from SPEX airborne data emphasize the key role of PACE-PAX in confirming aerosol properties derived from SPEXone.