Empirical chlorophyll algorithm and preliminary SeaWiFS validation for the California Current

Abstract

A new empirical chlorophyll algorithm is proposed for SeaWiFS (Seaviewing Wide Field-of-view Sensor) and other ocean colour sensors. The CAL-P6 algorithm uses a sixth-order polynomial of the ratio of normalized water leaving radiances (L WN) at 490nm and 555nm and is based on 348 measurements of L WN and chlorophyll- a in the California Current. Validation of the SeaWiFS-derived chlorophyll values with 27 concurrent in situ measurements showed high correlation (r2=0.93 in the log-log space) but significant overestimation by SeaWiFS at high chlorophyll- a concentration. The problem was traced to significant underestimation of the SeaWiFS-derived L W N (490) at high chlorophyll- a concentration (3-5mgm -3 ). Further refinement of the atmospheric correction is needed for SeaWiFS to attain its goal of 35% accuracy for chlorophyll retrieval in the coastal zone.