Empirical chlorophyll algorithm and preliminary SeaWiFS validation for the California Current

Abstract. Anewempirical chlorophyll algorithm is proposed for SeaWiFS (Sea-viewingWide 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 situmeasurements showed high correla-tion (r2=0.93 in the log ± log space) but signi ® cant overestimation by SeaWiFS at high chlorophyll-a concentration. The problem was traced to signi ® cant under-estimation of the SeaWiFS-derived L WN (490) at high chlorophyll-a concentration (3 ± 5mgmÕ 3). Further re ® nement of the atmospheric correction is needed for SeaWiFS to attain its goal of 35 % accuracy for chlorophyll retrieval in the coastal zone. 1