Estimating chlorophyll concentration in Lake Malawi from MODIS satellite imagery

This paper describes results of research to develop algorithms for estimating chlorophyll-a concentrations in Lake Malawi from MODIS satellite imagery. A procedure relating chlorophyll concentration in Lake Malawi to the atmospherically corrected reflectance ratio of MODIS/AQUA (Ocean Color) bands 9 and 12 (i.e., R443/R551) was established using the SeaWIFS Data Analysis System (SeaDAS) software, and shows a moderate relationship between in situ chlorophyll-a concentration and values obtained from satellite imagery. The results have potential application in monitoring the trophic state of Lake Malawi. Attempts to use Level 1B MODIS/Terra data proved futile because of lack of atmospheric correction in processing the reflectance data. This shows that atmospheric effects have serious impacts on radiant energy, and hence the need for atmospheric correction. This may be described as the correction made to remotely sensed radiance to account for effects related to the intervening atmosphere between the earth’s surface and the satellite sensor, the result being an estimate of spectral reflectance as it would have been measured at ground level.