The combined use of optical remote sensing data and unattended flow‐through fluorometer measurements in the Baltic Sea

Abstract

Global algorithms for chlorophyll‐a (chl‐a) concentration and primary productivity retrieval from satellite observations are often not applicable to areas that are turbid and rich in coloured dissolved organic matter (CDOM), such as the Baltic Sea. Such a turbid (Case 2) water area, with its unique optical properties, often requires a parametrization to local conditions. Water quality algorithms are also sensitive to other naturally occurring phenomena, such as temporal variations in the atmospheric properties. Therefore, adequate reference data are essential for the estimation of water quality algorithm accuracy. In this study, a comparison with Sea‐viewing Wide Field of view Sensor (SeaWiFS) data and high‐frequency flow‐through fluorometer measurements is made. These so‐called ‘ship of opportunity’ data are measured with an automated continuous sampling system onboard several merchant and passenger ships in the Baltic Sea (SOOP, the Alg@line‐system). The study is concentrated on the monitoring of spring blooms in the years 1999 and 2000. By combining Alg@line observations with satellite instrument observations, the strengths of both data sources are obtained. The Alg@line‐fluorometer data ensure a sufficient amount of field samples to parametrize remote sensing chl‐a algorithms. Information with a full spatial coverage on chl‐a fluctuations can be obtained through the use of remote sensing data.