The Extent of Urbanization in the Southwest As Viewed from Space

National Oceanic and Atmospheric Administration and USAF Defense Meteorological Satellite Program

Land in the Southwest is being rapidly transformed through the process of urbanization. This process has been particularly rapid due to the very high population growth rates in this region since WWII. Between 1950 and 1990, the population of the Southwest has tripled.

Nighttime images of the earth provide a dramatic picture of the extent and location of urbanized areas on the earth's surface. Figures 1 and 2 show the light produced by towns, cities, and industrial facilities throughout the Southwest as seen by U.S. Air Force DMSP satellites at night. Ephemeral light sources seen by the satellites, such as lightning, fires, and gas flares have been removed as part of the data processing at NOAA's National Geophysical Data Center (Elvidge and others, 1997). The areal extent of the remaining light sources, which are associated with urban areas, is highly correlated with electric power consumption and population. Based on these images, the total amount of land that is now classified as urban in the six southwestern states (Arizona, California, Colorado, Nevada, New Mexico, and Utah) is estimated to be 37,504 km². Nighttime images of the earth from space will provide an important tool for monitoring the extent and location of urban growth within the Southwest in the future.

Figure 1

Figure 1 clearly shows both major urban areas and the smaller towns and cities. For Figure 2, the sensitivity of the satellite sensors was reduced to reveal the intensity of light from the cores of major urban areas; red represents the brightest concentration of lights while yellow is the next brightest. As seen from space, Las Vegas is the brightest city on earth.

Figure 2

For more information

Elvidge, C.D., K.E. Baugh, E.A. Kihn, H.W. Kroehl, and E.R. Davis, 1997, Mapping City Lights with Nighttime Data from the DMSP Operational Linescan System, Photogrammetric Engineering and Remote Sensing, Vol. 63, pp. 727-734.

Elvidge, C.D., K.E. Baugh, E.A. Kign, H.W. Kroehl, E.R. Davis, and C.W. Davis, 1997, Relation Between Satellite Observed Visible-Near Infrared Emissions, Population, Economic Activity and Electric Power Consumption, International Journal of Remote Sensing, Vol. 18, No. 6, pp. 1373-1379.

Elvidge, C.D., Baugh, K.E., Hobson, V.H., Kihn, E.A., Kroehl, H.W., Davis, E.R., Cocero, D., 1997, Satellite inventory of human settlements using nocturnal radiation emissions: A contribution for the global toolchest. Global Change Biology, In Press.

Imhoff, M.L., W.T. Lawrence, D.C. Stutzer, and C.D. Elvidge. A Technique for Using Composite DMSP/OLS "City Lights" Satellite Data to Accurately Map Urban Areas, accepted by Remote Sensing of the Environment.

U.S. Department of the Interior | U.S. Geological Survey
URL: http://geochange.er.usgs.gov/sw/changes/anthropogenic/city_lights/
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