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ROSES Proposals

Aerosol Absorption Retrievals from Base-Line OCI Observations: Risk Reduction for Atmospheric Correction of the PACE Mission

PI: Lorraine Remer - University of Maryland Baltimore County
Aerosol absorption is a key aerosol parameter required for quantification of direct aerosol radiative forcing and has been linked to changes in atmospheric circulations and large scale precipitation patterns and to cloud macrophysical properties over large regions. Thus, a satellite aerosol product that quantifies absorbing aerosols will make a significant contribution to climate science. Absorbing aerosols also confuse atmospheric correction over oceans and interfere with determination of ocean water-leaving radiances, even at low aerosol loading. Thus, both the atmospheric and oceanic communities are united by their need to identify and quantify absorbing aerosols over the global oceans. The Pre-Aerosols-Clouds-Ecosystem (PACE) mission will attempt to push oceanographic science a full step forward by defining the Ocean Color Instrument (OCI) with hyperspectral capability from the ultraviolet (UV) to the near-infrared (NIR), and with additional wavelengths in the shortwave infrared (SWIR). We propose here that the basic PACE OCI instrument, with no enhancement, will also make a significant improved contribution to aerosol science. OCI is an exciting instrument for aerosol scientists because it will be the first truly broad spectrum U.S. instrument, effectively combining the aerosol-retrieval capabilities of MODIS and OMI, but on the same instrument, at the same spatial resolution. Sensitivity tests tell us that we should be able to retrieve 3 pieces of aerosol information from this configuration: nominally loading, absorption and either particle size or layer height. These published sensitivity tests are far from complete and they do not cover the wide range of circumstances that are required to identify optimal wavelength configurations and retrieval assumptions necessary to prepare for producing an aerosol product from OCI. Here we propose a series of theoretical studies to determine the uncertainties involved in 1) identifying absorbing aerosol at low aerosol optical depth (AOD) for the purposes of atmospheric correction, and 2) retrieving aerosol information including AOD and absorption at moderate to high AOD. Our focus is on the over ocean retrievals, where the new broad spectrum OCI offers enhanced possibilities, but this will be overlaid on a global (ocean and land) product that would represent adapting existing OMI and MODIS algorithms to OCI radiances. We are offering a perspective towards atmospheric correction that is aerosol-centered, proposed by investigators who are undisputed experts in aerosol retrieval from an OCI type of sensor. This work represents the major theoretical exploration and defining of uncertainties necessary for producing an operational product from satellite data. In addition, the PI (Remer) is volunteering to serve in a leadership capacity on the PACE Science Team.