Using Landsat imagery, we have been assessing lake water clarity in Minnesota, USA for over 25 years. For early assessments, we used empirical methods and in situ Secchi calibration data. Recent advances in satellite technology (improved spatial, spectral, radiometric, and temporal resolution) and atmospheric correction, along with cloud and supercomputing capabilities, have enabled the development of automated regional-scale measurements of water quality. These new capabilities provide opportunities to improve lake and fisheries management by measuring more variables (chlorophyll, colored dissolved organic matter (CDOM), and total suspended matter, the main determinants of water clarity, more frequently.
The progression from traditional image processing methods to near real-time monitoring is described in the next three sections: