Impact of Climate Change and Land Use on the Southwestern United States

Human impacts on the landscape

Southwest U.S. Change Detection Images from the EROS Data Center

Las Vegas, Nevada

by Kristi Sayler, U.S. Geological Survey

A matched pair of satellite images from different years can be processed into a new change-detection image, which shows areas of increased or decreased brightness, greenness, or wetness. These images can be used to monitor landscape changes. These images of Las Vegas, Nevada, show some effects of human activities on the landscape:

Surface disturbance
Increased surface brightness may indicate surface disturbance due to construction or excavations for construction including road resurfacing or paving.
Urban expansion
The increasing urbanization in the Southwest is manifest through increases in both brightness and greenness. These increases result, respectively, from both additional housing and development and expansion of golf courses.
Quarry operations and reservoir change
Increased surface brightness may result from expansion of gravel or rock quarry operations. As reservoirs are filled, brightness and greenness decrease in the reservoir proper and brightness increases around the outside of the reservoir.

Las Vegas 9-10-1986 Las Vegas 9-10-1992
Las Vegas 9-10-1986 Las Vegas 9-10-1992
Change from 1986 to 1992
Las Vegas 1992 - 1986

How these images were produced

The change detection contained in the following pages is done using Landsat multispectral scanner (MSS) and thematic mapper (TM) data to identify and characterize landscape change. The change analysis procedure involves:
  1. co-registering multiple dates of MSS or TM data,
  2. transforming the imagery to scene-based measures of brightness, greenness, and wetness (TM data only),
  3. pairwise differencing of the brightness, greenness, and wetness measures to compute change vectors (magnitude and direction) for each image pixel,
  4. encoding the change vectors using hue, saturation, and value (HSV) for visualization, and
  5. formulating a signal-to-noise model by which to isolate areas of significant change.

color key

The color key, shown here, is the model used to encode the calculated change vectors produced for each pair of images. It can be used to interpret the change images contained within the following web pages. An increase in greenness is shown as green and a decrease in greenness is shown as magenta. A decrease in brightness is shown as various shades of blue and an increase in brightness is shown as orange/red tones. Any combination of brightness and greenness changes will be shown somewhere on the color key. Shades of grey imply no change or change that was not considered significant.


For a more detailed description of the techniques or algorithmns used consult the following conference proceedings article:

Dwyer, J., Sayler, K., and Zylstra, G. 1996. Landsat pathfinder data sets for landscape change analysis. Proceedings of International Geoscience and Remote Sensing Symposium. Lincoln, Nebraska, May 27-31, 1996.


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