1. ASSESSMENT OF OPTICAL CLOSURE USING THE PLUMES AND BLOOMS IN-SITU OPTICAL DATASET, SANTA BARBARA CHANNEL, CALIFORNIA Tihomir S. Kostadinov, David A. Siegel, Stephane Maritorena & Nathalie Guillocheau Institute for Computational Earth System Science, University of California at Santa Barbara Optical Closure Formulae and Models Tested Abstract: The Plumes and Blooms (PnB) Project has collected an extensive data set of in-situ optical and oceanographic observations for 7 stations along a transect across the Santa Barbara Channel, California. Inherent optical properties (IOPs), such as spectral absorption, a( ), beam attenuation, c( ), and backscattering coefficients, b b ( ), and apparent optical properties (AOPs), such as the vertical attenuation coefficient for downward irradiance, K d ( ), and remote-sensing reflectance, R RS ( ), are collected to build and validate ocean color algorithms for Case II waters. Available optical closure relationships are evaluated including the single scatter approximation and Kirk’s (1984) relationship for K d. For R RS, the Gordon et al. (1988) approximation is used. Additionally, the f/Q value is estimated from our in-situ data and compared to literature values. Data are also evaluated against existing models relating IOPs and AOPs to chlorophyll concentrations. The investigated relationships suggest ways to quality control data before using them to develop semianalytic bio-optical algorithms. Results indicate that the closure formulae for K d perform well suggesting that the in-situ absorption determinations are of adequate quality. However, comparisons for R RS are worse suggesting difficulties in the PnB in- situ backscattering determinations. The measured backscattering coefficient seems to be underestimated for high R RS values, which influences regression statistics significantly. Plumes and Blooms Data Collected This work is supported by NASA’s Earth System Science Fellowship. The Plumes and Blooms Project has been funded by NASA as well. The authors are grateful to the staff on the NOAA R/V Shearwater as well as the engineering and data processing team of the Plumes and Blooms Project. Results Summary  Closure relationships generally hold well for the PnB data set  K d ( ) closures work well; absorption/attenuation meter and radiometer data are reliable.  Tests involving b b are worse: b b ( ) seems to be underestimated in high R RS ( ) cases. More data are needed. Carder et al. (1999) b b ( ) model works very well.  Estimates of f/Q are consistent with the literature.  Indicates that these data will be useful for modeling Case II ocean color. Future Research Direction  Relate IOP/AOP data to independent measures of sediment concentration (lithogenic silica).  Use the QC’ed data to locally tune the GSM01 semi-analytical bio-optical algorithm.  Validate the tuned algorithm.  Tune algorithm for different Case II sites.  Create a unified Case II semi-analytic algorithm. Quasi-Inherency Tests Exploring the f/Q ratio Models tested against PnB data b b ( ) vs R RS ( ) Derived Properties Data Acquisition, Processing & Analysis  Observations  Surface means for 7 PnB stations for 2001 to 2003.  WetLabs AC-9  a( ) & c( ); b( ) = c( ) – a( ). Standard corrections were performed. N = 206.  HobiLabs Hydroscat-6  b b ( ). Sigma correction was performed using AC-9 data. Spectral slope, , from b bp ( ) = b bp ( o )(  o ) -  was calculated for each spectrum. N = 73.  Biospherical Instruments PRR-600  L u (   , E d (   ) & K d (  0m). R RS (,0 - ) = L u (,0-)/E d (,0-). N = 262. Current Research Goals  Understand IOP/AOP relationships for Case II ocean waters.  Evaluate IOP/AOP data quality using closure formulae.  Build a quality assured IOP/AOP data set for the Santa Barbara Channel to use in ocean color modeling. Slope of the backscattering spectrum as a function of chlorophyll High chlorophyll  large particles  low spectral slope  Low chlorophyll  small particles  high spectral slope  The single scatter albedo spectrum,  o ( ) = b( )/c( ), is plotted on the left. Note that it resembles the reflectance spectrum. The backscattering probability, b b ( )/b( ), is plotted on the right. Morel and Maritorena 2001 model output Chlorophyll-normalized non-water absorption spectrum Matches the Bricaud et al. 1998 model for [chl] = 2.57 mg/m 3 (mean obs). Suggests that chlorophyll is the major light absorber. Solid lines show the f/Q values as computed with all available data; Dashed lines show f/Q computed when the few highest R RS values are excluded (they correspond to a coccolithophore bloom, as suggested by HPLC data). Earth System Science Fellowship Chlorophyll vs. AOPs Other Results Slope = f/Q Gordon et al. Quasi-Inherency Test Kirk Quasi-Inherency TestSingle Scatter Quasi-Inherency Test Morel and Maritorena 2001 Gordon et al. 1988 Carder et al. 1999 Wavelength, nm  o ( ) b b ( )/b( ) Chl-a, mg.m -3  of particulate backscatter Bricaud et al. 1998 a p /[Chl] Bricaud et al. 1998 a ph * Slope of linear regression of a( ) – a w ( ) vs. [Chl] Wavelength, nm f/Q, sr -1 f/Q 95% ci The f/Q factor obtained by regressing b b ( )/(a( )+b b ( )) vs PRR R RS (   ) Wavelength, nm Chl-a, mg.m -3 R RS (,0 +,chl-a), sr -1