Mapping lake water clarity with Landsat images in Wisconsin, U.S.A.

Landsat thematic mapper (TM) and enhanced thematic mapper plus (ETM+) images are being used to map lake water clarity region-wide in the Upper Midwest states of Minnesota, Wisconsin, and Michigan using a standardized image processing protocol. In Wisconsin, lake clarity estimates have been produced for 8645 lakes in the 1999-2001 time period. In addition to satellite imagery, the protocol relies on Secchi disk data collected by a network of citizen volunteers for development and validation of models. The most significant term in the regression model relating the satellite imagery to the field data is the ratio of spectral radiance values in the blue and red bands (ratio of Landsat band 1 to Landsat band 3). The resulting database of satellite-derived lake water clarity estimates represents an important new resource for lake managers in the region, and for those studying the linkages between lakes and their surrounding landscapes.