Journal of Oceanography, Vol. 56 (No. 3), pp. 245-260, 2000
Toru Hirawake1*, Hiroo Satoh1, Takashi Ishimaru1, Yukuya Yamaguchi1 and Motoaki Kishino2
1Department of Ocean Science, Tokyo University of Fisheries,
5-7, Konan 4, Minato-ku, Tokyo 108-8477, Japan
2Institute of Physical and Chemical Research (RIKEN), 2-1, Hirosawa,Wako-shi, Saitama 351-0198, Japan
(Received 16 April 1999; in revised form 27 September 1999; accepted 27 September 1999)
Abstract: Both historic and currently operational chlorophyll algorithms of the satellite-borne ocean color sensors, such as SeaWiFS, were evaluated for in situspectral 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 SeaWiFS 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 aconcentration, and the value in the Southern Ocean was significantly lower than that in the low- and mid-latitude waters for each chlorophyll aconcentration. The underestimation of chlorophyll aconcentration 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 aconcentration.