International Ocean Color Science Meeting , Darmstadt , Germany, May 6-8, 2013

1. Assessment of MODIS-Aqua Ocean Color and Aerosol Products in the US Northeastern Coastal Region using AERONET-Ocean Color Measurements, Hui Feng1, Heidi Sosik2 , and Tim Moore1 1: University of New Hampshire; 2 :Woods Hole Oceanographic Institution I. Introduction Validation for satellite retrieval product quality requires high-quality in-situ measurements and matchup analysis. One aspect of a NASA-Ocean Biology and Biogeochemistry program funded project focuses on the coastal satellite ocean color validation near the Martha’s Vineyard Coastal Observatory (MVCO) in Massachusetts (Figure 1). A key field component monitors the spectral water-leaving radiances and aerosol optical properties using an above-water automatic sun-photometer, the AERONET-Ocean Color (AERONET-OC, i.e., SeaPRISM) deployed at the MVCO tower since 2004. Our earlier studies have shown that MODIS-Aqua ocean color products produced by SeaDAS version 6.X with a new atmospheric correction scheme (Ahmad et al., 2010; Bailey et al., 2010) improves MODIS-Aqua ocean color products. Recently, a major reprocessing for the MODIS-Aqua ocean color data was released to address issues with instrument degradation, particularly from 2010 to the present. This study presents the following three parts: 1) an inter-comparison of MODIS-Aqua ocean color products by reprocessing 2012 (R2012.0) and by reprocessing 2010 (R2010) in terms of AERONET-OC measurements as a reference (Section III); 2) a cross validation of MODIS aerosol retrieval products by Ocean Color (OCN) and Atmosphere (ATM) research team algorithms based on the northeast coastal AERONET measurements ( Figure1, and Section IV); and 3) a validation of MVCO QAA-retrieved absorption components from SeaPRISM radiance measurements vs. directly measured ones ( Section V). II. Location and Platform MVCO COVE • Figure 1. Regional map including 10 coastal AERONET areas (red spots ), 3 of them over ocean, along the US eastern coastal region. At MVCO, the Air-Sea Interaction Tower(ASIT) is located about 3 km offshore at 15.6 m water depth. An AERONET-OC sun-photometer (i.e., SeaPRISM) unit is now mounted on ASIT. IV. Cross validation of MODIS aerosol properties by Ocean Color (OCN) and Atmosphere (ATM) teams • MODIS-Aqua normalized water leaving radiance nLw III.1. R2010 vs. R2012 vs. SeaPRISM at MVCO (c) (a) (b) • Data Sources • - MODIS-ATM on Aqua: Collection 5 • - MODIS-OC on Aqua: SeadAD 6.4 • - AERONET Level-2 data from 10 sites (3 over oceans) (Figure 1) • - 2002-2011 Collocation A circle area with a 25km radius, centering - At AERONET oceanic sites - ocean locations closet to AERONET land sites - Only oceanic pixels used for MODIS-ATM - ±30min time window between AERONET and MODIS pass time (a) (b) (c) (d) (e) (f) Figure 4. Scatter plots of means of the collocated MODIS-OC versus MODIS-ATM aerosol optical thickness (a) a(550), (b) a(870) and (c) the Ångström exponent α(550, 870). The error bars represent the respective standard deviations. The 1-1 lines are shown as the diagonal dash lines, while the solid lines give the linear regression fits with their corresponding equations and correlation coefficient R given in the upper left. N is the number of match-up pairs, and Φ and |Φ| indicate mean percent difference and absolute mean percent difference between MODIS-OC against MODIS-ATM, respectively. Figures 2a/b/c (upper panels). MVCO match up scatter plots of MODIS-nLw R2012 vs. R2010 (red cross), MODIS-nLw R2010 vs. SeaPRISM (blue circle) and MODIS-nLw R2012 vs. SeaPRISM (black cross). Figures 2d/e/f (lower panels). Time series of MODIS-Aqua normalized water leaving radiance for reprocessing R2010 (blue dot), reprocessing R2012 (red circle) and SeaPRISM in situ measurements (black star) at the MVCO site. (a)/(d) for 412nm, (b)/(e) for 443nm and (c)/(f) for 531 nm. III.2. R2010 vs. R2012 vs. SeaPRISM at other sites (a) (b) (c) (a) (b) (c) Figure 5. Scatter plots of means of the collocated MODIS-ATM versus AERONET aerosol optical thickness (a) a(550), (b) a(870) and (c) the Ångström exponent α(550, 870). All other caption texts are the same as whose in Figure 4. (e) (f) (d) (a) (b) (c) Figures 3a/b/c (upper panels). Match up scatter plots of MODIS-nLw R2012 vs. R2010 (red cross), MODIS-nLw R2010 vs. SeaPRISM (blue circle ) and MODIS-nLw R2012 vs. SeaPRISM (black cross). Figures 3d/e/f (lower panels). Time series of MODIS-Aqua normalized water leaving radiance for reprocessing R2010 (blue dot), reprocessing R2012 (red circle) and SeaPRISM in situ measurements (black star). (a)/(d) for 412nm at COVE, (b)/(e) for 531nm at COVE and (c)/(f) for 412 nm at a deep ocean siter. Figure 6. Scatter plots of means of the co-located MODIS-Ocean color versus AERONET aerosol optical thickness (a) a(550), (b) a(870) and (c) the Ångström exponent α(550, 870). All others are the same as Figure 4. • VI. Brief Summary • The AERONET-OC instrument deployed at MVCO has provided a valuable long time series of in-situ measured ocean color and aerosol properties for regional coastal ocean color validation efforts. • The trend from 2011 to 2012 suggests that the MODIS-nLw412 has decreased. Between reprocessing R2012 and R2010 there are slight differences in nLw at 443nm and little differences at longer wavelength (Figures 2-3). • Cross-validation (Figures3-5) of MODIS-OCN and MODIS-ATM aerosol retrievals shows aerosol optical thickness from both MODIS products are highly correlated, but the accuracy in Angstrom exponent retrievals remain quite low. • SeaPRISM-radiance based QAA absorption component retrievals: aT, adg, and aph is validated with in situ measurements and show reasonably good performance (Figure 7) . Regional QAA retuning to in situ data may further improve its performance. • AERONET-OC based QAA vs. insitu absorptions (c) (a) (b) Figure 7. Scatter plot showing the comparison between logrithm‐transformed AEROENT-OC (i.e., SeaPRISM) radiance based QAA retrieved absorption components: (a) aT (total absorption ); (b) adg and (c) aph, 531 (e). Different wavelenths are indicated by different colors Acknowledgements : This work has been sponsored supported by 1) NASA OBB programs (NNX11AF07G ) and 2) NASA (NNX11AL20G). The GSFC DAAC is also acknowledged for providing the MODIS –Aqua ocean color and Atmosphere data. International Ocean Color Science Meeting, Darmstadt, Germany, May 6-8, 2013