Chlorophyll A


The chlorophyll concentration in the water is one of the factors that affect the colours of the oceans. Measurements of the reflected sunlight in different spectral bands can therefore be used to estimate the amount of chlorophyll-a, which is an indicator of the amount of algal biomass in the water.

The images to the right shows an example of an algae bloom occurring in Danish waters during March 2011. It shows increasing levels of algae concentration in the inner Danish waters reaching potential harmful concentration levels to e.g. aquaculture installations. This spring bloom was of unseen magnitude; with the maps produced by GRAS it was possible to follow both the spatial and temporal development of the bloom, identify areas with potential harmful algae concentrations and analyse the overall magnitude of the event.

Since 2001 GRAS has been involved in operational Chlorophyll-a mapping and a number of operational systems have been designed. GRAS is currently capable of delivering daily Chlorophyll-a maps from both SeaWiFS, MODIS Aqua and MERIS. From MODIS Aqua worldwide daily coverage is possible with only a few hours delay from acquisition to processed product.

The data are processed to comply with the end-users’ need in terms of geographic coverage and data format. Access to data is either through ftp upload directly to the end-users’ ftp-server or by end-user download from the ftp server at GRAS following an email notification sent every time new data is made available.

Chlorophyll-a maps can be used for a wide range of applications e.g. indicator of water quality, warning systems for harmful algae blooms, assimilation and validation of oceanographic models and temporal analysis of algae distribution patterns as indicators of changes to the aquatic environment e.g. due to eutrophication.