A14C-04
Developing a joint MODIS and VIIRS aerosol data record using the dark-target retrieval algorithm
Monday, 14 December 2015: 16:45
3006 (Moscone West)
Robert C Levy, NASA/Goddard Space Flight Ctr, Greenbelt, MD, United States, Leigh A Munchak, NASA Goddard Space Flight Center, Greenbelt, MD, United States, Shana Mattoo, Science Systems and Applications, Inc., Lanham, MD, United States, Falguni Patadia, Goddard Earth Sciences Technology and Research, Greenbelt, MD, United States, Lorraine A Remer, University of Maryland Baltimore County, Baltimore, MD, United States and Robert Holz, UW SSEC, Madison, WI, United States
Abstract:
For more than a decade, NASA’s Moderate resolution Imaging Spectroradiometer (MODIS) sensors have provided quantitative information about aerosol optical depth (AOD) over land and ocean and Angstrom Exponent (AE) over ocean. Yet, this period is still too short to create an aerosol climate data record (CDR) and rigorously detect aerosol trends. The Visible Infrared Imaging Radiometer Suite (VIIRS) was launched on the Suomi-NPP satellite in late 2011, with additional copies planned for future satellites. Can the MODIS aerosol data record be continued with VIIRS to create a consistent CDR? By using consistent radiative transfer assumptions, and applying consistent thresholds for cloud masking and other pixel filtering, we have developed an initial version of the MODIS “dark-target” (DT) retrieval algorithm to be used on VIIRS. We have run this DT retrieval on global VIIRS data between March 2012 and May 2014, and compared the products with the routine Collection 6 products from MODIS aboard Aqua, as well as to the operational aerosol products from VIIRS provided by NOAA. Focusing on the March-April-May (MAM) 2013 period, we compared a number of statistics, including global averages and maps of AOD, histograms, sampling frequencies, and collocations with ground-based AERONET. Over land, use of the DT algorithm clearly reduced the discrepancy between VIIRS and MODIS -derived AOD. However, although global offsets are near zero, some regional biases remain, especially in cloud fields and over brighter surface targets. Over ocean, use of the DT algorithm on VIIRS increased the offset between VIIRS and MODIS –retrieved AOD (to ~0.025), but reduced the difference between AE. We characterized the retrieval fraction to show that DT algorithms on each sensor will make similar decisions about “whether to retrieve” on a given pixel. As examples of obstacles for a joint MODISàVIIRS aerosol CDR, we discuss issues of calibration, instrument spatial resolution, and cloud maskng based on shifted wavelength bands.
