Exploration of the potential for aerosol absorption retrievals from the expanded spectral range of the proposed PACE Ocean Color Instrument (OCI)

The proposed PACE Ocean Color Instrument (OCI) will provide high spectral resolution (5 nm) imagery from the UV to near-IR (350 - 890 nm) with additional spectral bands in the shortwave-IR (940, 1240, 1380, 1640, 2130 & 2250 nm). OCI would be the first satellite imager to span this broad spectral range of reflective solar bands. The OCI spatial resolution will be moderate, nominally 1 km at nadir, which is a slight step down from MODIS/VIIRS resolutions, but a giant step up when compared to similar UV imagers such as OMI. Thus, OCI is equivalent to merging MODIS and OMI into a single instrument, co-registered and with common calibration and common moderate spatial resolution. We have explored the possibilities of making use of OCI measurements to derive aerosol parameters, in particular examining the possibilities of using the UV channels to produce a measure of aerosol absorption. The method is based on the traditional Dark Target aerosol retrieval, so that we are determining the aerosol optical depth (AOD) and setting the size distribution using a nearly standard MODIS-like retrieval. Then we use the UV spectra to set the absorption properties. We show from sensitivity studies that the retrieval of absorption is not sensitive to most assumptions necessary for the method, and is insensitive to ocean color as long as aerosol loading is sufficiently high. Thresholds for measurements over ocean will require AOD at 550 nm to be greater than 0.3. Different methods that make use of the UV information to provide two pieces of information, absorption and height, are explored.