613 Seminar: Robert C. Levy


Using the Collection 6 (C6) version of the “dark-target” (DT) retrieval algorithm, NASA’s Moderate resolution Imaging Spectroradiometer (MODIS) sensors, on Terra and Aqua, each have provided over twelve years’ of validated information about aerosol optical depth (AOD) over land and ocean.  Related to MODIS, the current foci of our groups’ work includes:

1)         Quantifying discrepancies between Terra and Aqua-derived time series.
2)         Reducing the high bias over urban areas.
3)         Adding estimates of uncertainty to the product.

The DT algorithm includes strict cloud masking, so that we do not retrieve aerosol close to clouds.  Using enhanced-MODIS Airborne Simulator (eMAS) data that were collected from aircraft during the SEAC4RS experiment of 2013, we are applying the DT algorithm to the high-resolution observations.  Initial retrievals, while not yet validated, show interesting behavior of AOD next to clouds.

Additionally, as the MODIS sensors near their retirement, we are looking towards the planned series of Visible Infrared Imaging Radiometer Suite (VIIRS) sensors to continue the EOS-era aerosol data record.  It is essential that we understand the differences in the aerosol products from these instruments to create a viable long-term environmental data record.  We have developed and applied a DT retrieval algorithm for VIIRS (on Suomi-NPP) observations, and compared the results to C6 MODIS and operational VIIRS products.  For the period of March-April-May (MAM) 2013, the DT algorithm reduced the overall discrepancy between VIIRS and MODIS-derived AOD over land, but unexpectedly caused a large offset over ocean.