LANDSAT TM BASED QUANTIFICATION OF CHLOROPHYLL-A DURING ALGAE BLOOMS IN COASTAL WATERS

Simultaneous acquisition of Landsat TM imagery and sea truth data from sample sites in Himmerfjarden bay on the Swedish east coast was conducted on 10 May 1988, and 7 May 1990. The data were used to develop and verify regression models for the estimation of surface chlorophyll-a concentrations. The case 2 waters studied partly hold suspended sediment concentrations known to complicate the mapping of chlorophyll-a. The disturbing spectral influence from suspended sediment was reduced by using a process based on an existing Landsat TM sediment retrieval algorithm and a priori knowledge about water depths, bottom sediments and river outlets. The results suggest that a ratio of TM bands TM1/(log TM3 + 1) should be used in waters influenced by terrigenous influx and the earlier suggested ratio of TM bands 1/2 only in ocean waters. The discrimination power indicated a capability to quantify chlorophyll in connection with algae blooms.