Evaluation of ADEOS-II GLI ocean color atmospheric correction using SIMBADA handheld radiometer data |
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| Authors: | Hajime Fukushima Mitsuhiro Toratani Hiroshi Murakami Pierre-Yves Deschamps Robert Frouin Akihiko Tanaka |
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| Institution: | (1) School of High-Technology for Human Welfare, Tokai University, Numazu 410-0395, Japan;(2) Japan Aerospace Exploration Agency, Tsukuba 305-8505, Japan;(3) Laboratoire d’Optique Atmosphérique, Université des Sciences et Technologies de Lille, Villeneuve d’Asq. Cedex, France;(4) Scripps Institution of Oceanography, UCSD, La Jolla, CA, 92037, U.S.A.;(5) Institute for East China Sea Research, Nagasaki University, Nagasaki 852-8521, Japan |
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| Abstract: | The performance of the “version 2” Global Imager (GLI) standard atmospheric correction algorithm, which includes empirical absorptive aerosol correction and sun glint correction, was evaluated using data collected with handheld above-water SIMBADA radiometers during 23 cruises of opportunity (research vessels, merchant ships), mostly in the North Atlantic and European seas. A number of 100 match-up data sets of GLI-derived and SIMBADA-measured normalized water-leaving radiance (nL W ) and aerosol optical thickness (AOT) were sorted out, using objective selection criteria, and analyzed. The Root-Mean-Square (RMS) difference between GLI and SIMBADA nL W was about 0.32 µW/cm2/nm/sr for the 412 nm band, showing improvement by 30% in RMS difference with respect to the conventional “version 1” GLI atmospheric correction algorithm, and the mean difference (or bias) was reduced significantly. For AOT, the RMS difference was 0.1 between GLI estimates and SIMBADA measurements and the bias was small (a few 0.01), but the Ångström exponent was systematically underestimated, by 0.4 on average, suggesting a potential GLI calibration offset in the near infrared. The nL W differences were not correlated to AOT, although performance was best in very clear conditions (AOT less than 0.05 in the 865 nm band). Despite the relatively large scatter between estimated and measured nL W , the derived chlorophyll-a concentration estimates, applying the same ratio algorithm (GLI OC4V4) to GLI and SIMBADA, were consistent and highly correlated in the range of 0.05–2 µg/l. The large variability in chlorophyll-a concentration estimate for clear clean water areas (e.g. with the concentration range lower than about 0.05 µg/l) turns out to be due to the nature of the “band ratio” based in-water algorithm. |
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| Keywords: | Satellite remote sensing phytoplankton SIMBADA water-leaving radiance |
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