Improving satellite-retrieved aerosol microphysical properties using GOCART data

[摘要] The Multi-angle Imaging SpectroRadiometer (MISR) aboardthe NASA Earth Observing System's Terra satellite can provide more reliableaerosol optical depth (AOD) and better constraints on particle size(Ångström exponent, or ANG), sphericity, and single-scattering albedo (SSA) than many other satellite instruments. However, many aerosol mixturespass the algorithm acceptance criteria, yielding a poor constraint, when theparticle-type information in the MISR radiances is low, typically at lowAOD. We investigate adding value to the MISR aerosol product under theseconditions by filtering the list of MISR-retrieved mixtures based onagreement between the mixture ANG and absorbing AOD (AAOD) values, andsimulated aerosol properties from the Goddard Chemistry Aerosol Radiationand Transport (GOCART) model. MISR–GOCART ANG difference and AAOD ratiothresholds for applying GOCART constraints were determined based oncoincident AOD, ANG, and AAOD measurements from the AErosol RObotic NETwork (AERONET). The results were validated by comparing the adjusted MISR aerosoloptical properties over the contiguous USA between 2006 and 2009 withadditional AERONET data. The correlation coefficient (r) between theadjusted MISR ANG derived from this study and AERONET improves to 0.45,compared to 0.29 for the MISR Version 22 standard product. The ratio of theadjusted MISR AAOD to AERONET increases to 0.74, compared to 0.5 for theMISR operational retrieval. These improvements occur primarily whenAOD < 0.2 for ANG and AOD < 0.5 for AAOD. Spatial and temporaldifferences among the aerosol optical properties of MISR V22, GOCART, andthe adjusted MISR are traced to (1) GOCART underestimation of AOD and ANG inpolluted regions; (2) aerosol mixtures lacking in the MISR Version 22algorithm climatology; (3) low MISR sensitivity to particle type under someconditions; and (4) parameters and thresholds used in our method.

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