On July 23, the Landsat system will celebrate 40 years of continuous observations of the land forms of the planet. Over 7 million separate scenes have been collected by the six satellites in the series. The data from the satellites provide a permanent, objective record of land conditions and are routinely used to measure and monitor changes brought on by natural and anthropogenic events and actions. Floods, fires, tsunamis, urban growth, highway construction, mining, and clear cutting of tropical zone forests are among the studies illustrated by the data collected by Landsat satellites.
In 1972, the color infrared image processed from Landsat data illustrates the greater Washington, D.C. area. Intense red tones indicate forests and large grassy areas. Light tones indicate cleared fields and the highly reflective impervious areas of urban development, highways, and airport runways. The resolution of 1972 Landsat data was no better than 79 m. By 2012, Landsat sensors were offering data at 30 m, expanded band options, and limited 15 m data.
A comparison of the two images illustrates the significant growth in the greater D.C. area. Major urban development can be seen in surrounding communities including Rockville, Greenbelt, and Suitland, Maryland. The expanded Woodrow Wilson Bridge, connecting Springfield, Virginia, with Oxon Hill, Maryland, is evident, as is the Lake Barcroft reservoir between Falls Church and Alexandria.
The record of surface change is being used by urban planners and local and regional officials to evaluate the rate and direction of growth in the area.