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Introduction

Clearly, change, including in land cover and land use, is a constant. Humans have long altered the land by clearing forests, farming, and building settlements. Due to advances in civilization, human-induced changes now occur much faster, and in many ways more dramatically than in the past. It is increasingly apparent that these rapid transformations can have profound social and environmental implications. This can be seen in the Twin Cities of Minnesota, a 7,700 km2 seven-county region home to roughly 2.8 million people. Its population is forecast to top 3.5 million in 2020, building on a trend of the region being one of the fastest-growing metropolitan areas in the nation.

A New Approach

We integrate several different approaches to describe and understand the processes of urbanization and land use change in Minnesota 's metropolitan and rural areas. We start by creating maps of the changing landscape based on imagery taken from satellites orbiting the planet, an approach that offers an effective method for inventory, monitoring, and analysis of land, vegetation, and water resources.

This new approach offers several advantages:

  • Land cover and impervious maps and statistics for any location (i.e., city, county, watershed).

  • Large area coverage. Landsat satellite images cover over 11,000 square miles and multi-county areas, so the same image can be used to map different locations.

  • Landsat TM imagery has been acquired since 1984 so it is possible to evaluate changes in land use and imperviousness over time.

  • A digital format compatible with geographic information systems.

  • Time and cost savings due to digital classification methods being used instead of manual interpretation.

Land Cover and Imperviousness

We are interested in two particular kinds of information about Minnesota - the kind of land cover found in a given location (e.g., urban, agricultural, or forests) and the percentage of impervious surfaces, those like roads or parking lots that do not allow water to penetrate into the underlying soil. We also combine these maps of land cover and impervious surfaces with other data - such as census figures, political jurisdictions, or physical characteristics of the land - in a Geographic Information System, a computer system used to manipulate and analyze spatial data. In a related project (see water.rs.umn.edu) we are using the Landsat data to monitor lake clarity, an important indicator of water quality.

Teaming up to monitor change

With the advances in mapping from satellite imagery we are able to create a brand new resource - statewide maps that can track the whole picture of urban growth over time. What does it show us? That the key is where and how fast these changes are occurring. Rapid change (we have seen an increase almost doubling the amount of impervious surfaces statewide in 10 years) can come at a cost. Looking at this change has teamed researchers from the University of Minnesota 's Remote Sensing and Geographical Analysis Laboratory with scientists and planners from the Minnesota Pollution Control Agency and uses this website to provide the results of new impervious surface and land use change monitoring techniques to the public in the form of maps and statistics. We hope the results will be helpful to you in your local units and decisions.

A growing suburban area of the TCMA

A growing suburban area of the TCMA. Photo credit: Minnesota PCA website

We use imagery from a satellite named Landsat. Data have been acquired at various intervals between 1986-2002 to develop maps of land cover and impervious surface for the metro area, as well as the whole state. These images resemble those taken with a digital camera but the satellite senses both visible light (the colors that humans see) and infrared (wavelengths longer than those our eyes are sensitive to). Each image is composed of millions of picture elements, or 'pixels', each equivalent to a 30 x 30 meter area on the ground (about 1/4-acre).