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
|Change from 1986 to 1992
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:
- co-registering multiple dates of MSS or TM data,
- transforming the imagery to scene-based measures of brightness, greenness,
and wetness (TM data only),
- pairwise differencing of the brightness, greenness, and wetness measures
to compute change vectors (magnitude and direction) for each image pixel,
- encoding the change vectors using hue, saturation, and value (HSV)
for visualization, and
- formulating a signal-to-noise model by which to isolate areas of significant
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.