Bio-Optical Relationship of Case I Waters: The Difference between the Low- and Mid-Latitude Waters and the Southern Ocean |
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| Authors: | Toru Hirawake Hiroo Satoh Takashi Ishimaru Yukuya Yamaguchi Motoaki Kishino |
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| Institution: | (1) Department of Ocean Science, Tokyo University of Fisheries, 5-7, Konan 4, Minato-ku, Tokyo, 108-8477, Japan;(2) Department of Ocean Science, Tokyo University of Fisheries, 5-7, Konan 4, Minato-ku, Tokyo, 108-8477, Japan;(3) Institute of Physical and Chemical Research (RIKEN), 2-1, Hirosawa, Wako-shi, Saitama, 351-0198, Japan |
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| Abstract: | Both historic and currently operational chlorophyll algorithms of the satellite-borne ocean color sensors, such as SeaWiFS, were evaluated for in situ spectral radiation and chlorophyll data in some Case I waters, including the waters in the Indian Ocean sector of the Southern Ocean. Chlorophyll a concentration of the data set (n = 73) ranged from 0.04 to 1.01 mg m–3. The algorithms had higher accuracy for the low- and mid-latitude waters (RMSE: 0.163–0.253), specifically the most recently developed algorithms of OCTS and Sea WiFS showed 0.163 and 0.170 of Root Mean Square Errors, respectively. However, these algorithms had large errors (0.422–0.621) for the Southern Ocean data set and underestimated the surface chlorophyll by more than a factor of 2.6. The absorption coefficients in the blue spectral region retrieved from remote sensing reflectance varied in a nonlinear manner with chlorophyll a concentration, and the value in the Southern Ocean was significantly lower than that in the low- and mid-latitude waters for each chlorophyll a concentration. The underestimation of chlorophyll a concentration in the Southern Ocean with these algorithms was caused by the lower specific absorption coefficient in the region compared with the low- and mid-latitude waters under the same chlorophyll a concentration. |
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| Keywords: | chlorophyll a ocean color algorithm absorption Southern Ocean Case I water CZCS OCTS SeaWiFS |
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