SeaWiFS ocean colour chlorophyll algorithms for the southern Baltic Sea

Abstract

Simultaneous measurements of the remote sensing reflectance and chlorophyll-a concentration at nearly 700 stations in the Baltic Sea were collected in the years 1993-2001. The collected dataset was used for in situ validation of the standard Sea-viewing Wide Field of view Sensor (SeaWiFS) algorithms. The results confirm a large discrepancy between the observed chlorophyll-a concentrations and the concentrations calculated from the current SeaWiFS operational algorithm equations. New forms are proposed as chlorophyll algorithms for the SeaWiFS sensors or sensors with similar spectral bands. These forms include new coefficients and lower order of equations. As a two-band algorithm, a simple polynominal log-log equation is proposed: log(Chla)=-0.141-2.865R, where R is a band ratio equal to that of SeaWiFS OC2 algorithm. The four-band algorithm takes the form: log(Chla)=-0.028-3.9015R, where R is a band ratio equal to that of SeaWiFS OC4 algorithm. These new forms allow improving accuracy for chlorophyll retrieval in the Baltic. Further, a considerable improvement in the accuracy of the chlorophyll concentration estimated from remote sensing algorithms required the use of a new set of the spectral bands in the equations. An algorithm with such a new set of two spectral bands has the form: log(Chla)=0.738-4.681R, where R=log[Rrs(550)/ Rrs(590)]. The accuracy of this algorithm is much better than the previously mentioned algorithms and the authors propose application of the new spectral bands in future satellite sensors. © 2005 Taylor & Francis Ltd.