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A collaboration of the University of Minnesota's Remote Sensing and Geospatial Analysis Laboratory and Water Resources Center

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City Level
Eagan, Minnesota

High-resolution IKONOS satellite data with four multispectral bands similar to Landsat TM bands 1-4 are ideal for studying small lakes. To explore the capabilities of IKONOS satellite data for lake water quality assessment and monitoring, we acquired an August 23, 2000 IKONOS image for the City of Eagan, Minnesota. Eagan has 375 small lakes and ponds larger than one acre, with 44-acre Thomas Lake being the largest.

To map lake water clarity for Eagan, we first acquired Secchi disk measurements from 19 different lakes in Eagan that were collected within three days of the August 23, 2000 image.  Next, lake signatures were extracted from the image to model lake water clarity for all the lakes and ponds in Eagan. 

The model was developed using the band 1:3 ratio and band 1 as the independent variables and the natural log of Secchi measurements as the dependent variable. The relationship between the IKONOS measurements and the Secchi disk measurements had an R2 = 0.89 (an R2 value of 0 would indicate no relationship and a value of 1 would indicate a perfect relationship). This R2 value is very similar to the results using Landsat data at the metro and state scale.  Click on IKONOS vs. Secchi Disk Measurements in the right column to view this relationship.

Finally, we created a pixel level map of the water clarity of the small lakes and ponds in Eagan.  Click on the 2001 Eagan Lake Water Clarity map in the right column to enlarge the map, and view a close up of the southeast corner.

The use of IKONOS data (and similar data from the QuickBird satellite) for assessment of water clarity for small lakes at a city scale is promising. The high spatial resolution of the IKONOS data enables the assessment of smaller lakes and ponds than the Landsat 30-meter resolution allows. Only 14 of Eagan’s 375 ponds and lakes were included in our statewide assessment, while IKONOS data allows for the assessment of all of Eagan’s small lakes and ponds.

IKONOS data also would be useful for detailed city land use/cover and wetland mapping. These maps could be used to assess how land use/cover affects water clarity. The cost of the IKONOS data would be prohibitively expensive for regional assessments, but would likely be affordable by many cities.

At this city scale, what can influence lake water clarity?

  • Storm water runoff

  • Land use

  • Lake morphology

  • Proximity to sewage treatment facilities

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