Satellite Remote Sensing of Land Use Change

By Dr. Charles Laymon

The land in Madison County, Alabama has been developed at an observed annual rate of 1% per year for the last 16 years. In 2000, developed land comprised 30% of the county. At this rate, by 2020 nearly 50% of the county will be developed! ...At least that's what satellite images are telling us.

Urbanization worldwide continues at a rapid rate and it is estimated by the United Nation's Population Fund (1999) that by the year 2025, 80% of the world's population will live in cities. Most major metropolitan areas face the growing problems of urban sprawl; residential and commercial development is replacing undeveloped land at an unprecedented rate. Sprawl results in a loss of natural vegetation and open spaces and a general decline in the spatial extent and connectivity of wetlands, wildlife habitat, and agricultural lands. While land use changes are a consequence of national growth, regional assessments of historical and contemporary land use change are needed to anticipate the impacts associated with change and contribute to an understanding of productive environmental sustainability.

These land cover and land use changes can be substantial but are difficult to grasp when they occur incrementally. Recently, data from satellites has dramatically illustrated the rates at which these human-induced changes are occurring nationwide. Temporal mapping from satellite data has successfully demonstrated the utility of integrating existing historic maps with remotely sensed data and related geographic information to dynamically map urban land characteristics for large metropolitan areas. These regional databases provide a strong visual portrayal of recognized growth patterns, and dramatically convey how the progress of modern urbanization results in profound changes to the landscape.

Huntsville and Madison County, Alabama have continued to grow steadily since the 1950's. This growth has had a marked effect on the remaining green space within the County. The Land Trust of Huntsville and North Alabama, which is dedicated to preserving lands for public use to enhance recreation, education, conservation and prosperity in the North Alabama region, recognizes that some of this land is a valuable resource and worth protecting from urban sprawl.

To assist the Land Trust in acquiring data to develop a land resource plan for Madison County, a set of georeferenced maps based on satellite remote sensing was developed to document the spatio-temporal changes in land cover and land use that have occurred in Madison County since 1984. The spatio-temporal information afforded by satellite data can be used to illustrate where changes have occurred and to quantify the rate of urban sprawl and concomitant loss of green space. These data provide the basis for understanding urban growth changes within an historical perspective.

The land cover analysis was based on data from the Landsat series of satellites, which provide one of the most extensive and continuous terrestrial imagery archives. Since the beginning of the Landsat program in 1972, data have been acquired from three different generations of sensors, the Multispectral Scanner , Thematic Mapper and Enhanced Thematic Mapper Plus data. Landsat imagery of the globe is subset and marketed as a patchwork of individual scenes identified by a row and path designation. Images from Landsat's Thematic Mapper instrument were acquired for 1984 and 1990 and from Landsat's Enhanced Thematic Mapper instrument for 2000. Land surface features were assigned to one of 13 classes, such as commercial, residential, deciduous woodland, cropland, etc. The resulting images can then be processed mathematically to compute land area that has changed from one class to another.

To assess the change in land use over the 16-year period from 1984 to 2000, land cover/land use classes were aggregated into "Developed" and "Undeveloped" superclasses.The difference between these maps reflects changes in the distribution of Developed and Undeveloped land that has occurred during the intervening periods.

Between 1984 and 2000, Madison County experienced strong growth resulting in an increase in developed land area at an average rate of 1% per year. In all, 16.1% of the land in Madison County changed from Undeveloped to Developed. Development occurred nearly three times as fast between 1984 and 1990 than it did between 1990 and 2000. In 1984, 13.4% of the total land area of Madison County was developed.One area experienced nearly a 10-fold increase in Developed land area. The statistics for area of developed land in Madison County are consistent with population changes that have occurred in Madison County during the past two decades.

Once maps of land cover/use change are developed, these data can be integrated in a GIS environment with other types of planimetric data to compute change on other areal bases. For this project, change in developed land area was determined for individual cities and townships, real estate zones, and particular watersheds. These results lead to a more comprehensive interpretation of urbanization and may point to factors that have stimulated development in different areas or may identify potential consequences.

Observations of developed land area for 1984, 1990, and 2000 were projected into the future and suggest that 38% to 50% of the land in Madison County may be developed by 2020. These data will be valuable to the Land Trust in planning future land acquisitions and in educating and engaging the public in the need to preserve and enhance our community's natural resources before the losses are irretrievable.

Figure 1: Pseudo true-color satellite image of Madison County, Alabama.In 1990, 21.4% of the County was developed reflecting a 59.3% increase in the amount of Developed land. In 2000, 29.5% of the County was developed.(click on image for larger view)

Figure 2.Land cover/land use classification of Madison County, Alabama for May 2000

Figure 3.Maps showing the distribution of Developed and Undeveloped land in Madison County in 1984, 1990, and 2000.(click on image for larger view)

Figure 4.Map showing the distribution of Developed and Undeveloped land in Madison County that experienced no change in land use from 1984 to 1990 or from 1990 to 2000, and land that changed from Undeveloped to Developed.(click on image for larger view)

Figure 5.Maps showing the percent change in Developed land area for cities and townships in Madison County between 1984 to 1990 and 1990 to 2000.(click on image for larger view)

Figure 6.Map showing the location of real estate zones in Madison County for which land use change assessment was made.(click on image for larger view)

Figure 7.Chart showing the percent change in Developed land area between 1984 and 1990 and between 1990 and 2000 for real estate zones of Madison County.

Figure 8.Graph of Developed land area in Madison County, Alabama estimated from satellite imagery (observations) with extrapolation to 2020.

Figure 9.Map showing the distribution of Developed and Undeveloped land in Madison County in 2020 projected from observations of the same in 1984, 1990, and 2000.

Published Thursday, July 24th, 2003

Written by Dr. Charles Laymon

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