Remote sensing:  A tool to clean up Iowa's lakes?
	Digital model of terrain, Lake Casey watershed

   Measuring the water quality of a lake is a long, labor-intensive and costly process.  What if satellite imagery could provide a reliable and cost-effective alternative?  In Iowa, which is one of the worst states in the nation when it comes to water quality, this could be an important tool for remediation.
    That is what Michael Emch, assistant professor of geography at the University of Northern Iowa, and his student researchers are trying to find out.  With a $10,000 seed grant from the Iowa Space Grant Consortium, Emch and his students are using Landsat data from 1986-2000 to develop ways to assess the water quality of Iowa's lakes and land use change in their watersheds.
    Satellite imagery has commonly been used to analyze land use, but Emch is hoping that it can also be usefully applied to water quality.  Most studies of remote sensing applications of water have looked at larger bodies of water, such as Lake Michigan.  Emch is focusing on two Iowa lakes, Lake Casey in Tama County and Silver Lake near Delhi.
 
 

    Developing methods for using satellite imagery to assess water quality is just the first step.  Once they have this capability, the researchers can use remote sensing to study changes in residential and vegetation patterns in the watersheds of the lakes.  Then they can compare the data on water quality in the lakes with those on land use in the lakes' watersheds.  Although the relationships may not be conclusively cause-and-effect, the emerging patterns should show strong links.
    Preliminary data from the project suggest that water quality for one of the lakes, which is located in a state park, did not change significantly over time.  For the other lake, which is surrounded by farmland, however, the changes have been significant.

    Water quality measurements were taken for Lake Casey  and Silver Lake as part of the Iowa Water Quality Study, which is partially funded by the ISGC.  The water quality variables included dissolved oxygen, total and dissolved phosphorus, surface water temperature and chlorophyll a, which were regularly measured at most sites in both lakes during the summer of 1999.  Other varaibles, such as nitrate, cyanazine and atrazine levels were measured less regularly.
    Emch and his team have acquired satellite imagery from the Landsat Thematic Mapper, which passes over Iowa every 16 to 18 days in its orbit of the Earth, measures reflected energy at different wave lengths, and stores the data.  They are exploring different ways of combining data from different wave length bands in order to determine the most accurate formula for assessing water quality.
    To assess the accuracy and predictability of their formula, they are comparing their results with those obtained on the ground through the Iowa Water Quality Study.  The latter will serve as a benchmark against which to measure the data derived from satellite imagery.