Retrieving Aerosol Characteristics From the PACE Mission, Part 1: Ocean Color Instrument

NASA’s Plankton, Aerosol, Clouds, ocean Ecosystem (PACE) satellite mission is scheduled to launch in 2022, with the Ocean Color Instrument (OCI) on board. For the first time reflected sunlight from the Earth across a broad spectrum from the ultraviolet (UV: 350 nm) to the short wave infrared (SWIR: 2260 nm) will be measured from a single instrument at 1 km spatial resolution. While seven discrete bands will represent the SWIR, the spectrum from 350 nm to 890 nm will be continuously covered with a spectral resolutionof 5 nm. OCI will thus combine in a single instrument (and at an enhanced spatial resolution for the UV) the heritage capabilities of the MODerate resolution Imaging Spectroradiometer(MODIS) and the Ozone Monitoring Instrument(OMI), while covering the oxygen A-band. Designed for ocean color and ocean biology retrievals, OCI also enables continuation of heritage satellite aerosolproducts and the development of new aerosolcharacterization from space. In particular the combination of MODIS and OMI characteristics allows deriving aerosolheight, absorption and optical depthalong with a measure of particle size distribution. This is achieved by using the traditional MODIS visible-to-SWIR wavelengths to constrain spectral aerosol optical depthand particle size. Extrapolating this information to the UV channels allows retrieval of aerosolabsorption and layer height. A more direct method to derive aerosollayer height makes use of oxygen A-band absorption methods, despite the relative coarseness of the nominal 5 nm spectral resolutionof OCI. Altogether the PACE mission with OCI will be an unprecedented opportunity for aerosolcharacterization that will continue climate data records from the past decades and propel aerosolscience forward towards new opportunities.