dc.contributor.author	Levy, Robert C.
dc.contributor.author	Mattoo, Shana
dc.contributor.author	Sawyer, Virginia
dc.contributor.author	Shi, Yingxi
dc.contributor.author	Colarco, Peter R.
dc.contributor.author	Lyapustin, Alexei I.
dc.contributor.author	Wang, Yujie
dc.contributor.author	Remer, Lorraine A.
dc.date.accessioned	2018-09-12T19:13:56Z
dc.date.available	2018-09-12T19:13:56Z
dc.date.issued	2018-07-13
dc.description.abstract	Long-term measurements of global aerosol loading and optical properties are essential for assessing climate-related questions. Using observations of spectral reflectance and radiance, the dark-target (DT) aerosol retrieval algorithm is applied to Moderate Resolution Imaging Spectroradiometer sensors on both Terra (MODIS-T) and Aqua (MODIS-A) satellites, deriving products (known as MOD04 and MYD04, respectively) of global aerosol optical depth (AOD at 0.55µm) over both land and ocean, and an Ångström exponent (AE derived from 0.55 and 0.86µm) over ocean. Here, we analyze the overlapping time series (since mid-2002) of the Collection 6 (C6) aerosol products. Global monthly mean AOD from MOD04 (Terra with morning overpass) is consistently higher than MYD04 (Aqua with afternoon overpass) by ∼13% (∼0.02 over land and ∼0.015 over ocean), and this offset (MOD04 – MYD04) has seasonal as well as long-term variability. Focusing on 2008 and deriving yearly gridded mean AOD and AE, we find that, over ocean, the MOD04 (morning) AOD is higher and the AE is lower. Over land, there is more variability, but only biomass-burning regions tend to have AOD lower for MOD04. Using simulated aerosol fields from the Goddard Earth Observing System (GEOS-5) Earth system model and sampling separately (in time and space) along each MODIS-observed swath during 2008, the magnitudes of morning versus afternoon offsets of AOD and AE are smaller than those in the C6 products. Since the differences are not easily attributed to either aerosol diurnal cycles or sampling issues, we test additional corrections to the input reflectance data. The first, known as C6+, corrects for long-term changes to each sensor's polarization sensitivity and the response versus the scan angle and to cross-calibration from MODIS-T to MODIS-A. A second convolves the detrending and cross-calibration into scaling factors. Each method was applied upstream of the aerosol retrieval using 2008 data. While both methods reduced the overall AOD offset over land from 0.02 to 0.01, neither significantly reduced the AOD offset over ocean. The overall negative AE offset was reduced. A collection (C6.1) of all MODIS Atmosphere products was released, but we expect that the C6.1 aerosol products will maintain similar overall AOD and AE offsets. We conclude that (a) users should not interpret global differences between Terra and Aqua aerosol products as representing a true diurnal signal in the aerosol. (b) Because the MODIS-A product appears to have an overall smaller bias compared to ground-truth data, it may be more suitable for some applications. However (c), since the AOD offset is only ∼0.02 and within the noise level for single retrievals, both MODIS products may be adequate for most applications.	en_US
dc.description.sponsorship	This work was supported by the NASA ROSES program NNH13ZDA001N-TERAQEA: Terra and Aqua – Algorithms – Existing Data Products and NASA’s EOS program managed by Hal Maring. We thank MCST for their efforts in maintaining and improving the radiometric quality of MODIS data, and LAADS/MODAPS for the continued processing of the MODIS products. We are grateful to Yaping Zhou and Falguni Patadia (Morgan State University/GSFC) and Pawan Gupta (USRA/GSFC) for reviewing early drafts of this paper.	en_US
dc.description.uri	https://www.atmos-meas-tech.net/11/4073/2018/amt-11-4073-2018.html	en_US
dc.format.extent	20 pages	en_US
dc.genre	journal article	en_US
dc.identifier	doi:10.13016/M2T727K37
dc.identifier.citation	Robert C. Levy, Shana Mattoo, Virginia Sawyer, Yingxi Shi, Peter R. Colarco, Alexei I. Lyapustin, Yujie Wang, Lorraine A. Remer: Exploring systematic offsets between aerosol products from the two MODIS sensors, Atmospheric Measurement Techniques, Volume 11 issue 7, 4073-4092, https://doi.org/10.5194/amt-11-4073-2018, 2018.	en_US
dc.identifier.uri	https://doi.org/10.5194/amt-11-4073-2018
dc.identifier.uri	http://hdl.handle.net/11603/11283
dc.language.iso	en_US	en_US
dc.publisher	Copernicus Publications	en_US
dc.relation.isAvailableAt	The University of Maryland, Baltimore County (UMBC)
dc.relation.ispartof	UMBC Joint Center for Earth Systems Technology
dc.relation.ispartof	UMBC Faculty Collection
dc.rights	This item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.
dc.rights	Attribution 4.0 International (CC BY 4.0)	*
dc.rights.uri	https://creativecommons.org/licenses/by/4.0/	*
dc.subject	overlapping time series	en_US
dc.subject	Goddard Earth Observing System	en_US
dc.subject	measurement of global aerosol loading and optical properties
dc.subject	observations of spectral reflectance and radiance
dc.subject	dark-target (DT) aerosol retrieval algorithm
dc.subject	Moderate Resolution Imaging Spectroradiometer sensors
dc.subject	global aerosol optical depth
dc.subject	Ångström exponent
dc.subject	analysis of overlapping time series
dc.subject	variability of measurements
dc.subject	global differences between Terra and Aqua aerosol products
dc.title	Exploring systematic offsets between aerosol products from the two MODIS sensors	en_US
dc.type	Text	en_US

Exploring systematic offsets between aerosol products from the two MODIS sensors

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