This landsat image was taken by Thematic Mapper instrument of Landsat 4 on November 2, 1982 from an altitude of 438 miles. The complete image is 7168 pixels across by 5972 pixels high in each of seven spectral bands and originally came on seven 9-track magnetic tapes. For this image every 10th pixel of every 10th line has been displayed. This image, Scene ID 84004515151XO, is explored in more detail in this web document. Other related information is available through the Global Land Information System
The actual dimensions of this scene are about 127 by 106 miles (204 by 170 km). The measured pixel size is about 28.5 meters for this image. True north is about 10 degrees to the left of straight up.
The 7 spectral bands are: blue, green, red, and 4 infrared. These bands may be combined in various combinations. One way to display multiple spectral bands is to color 3 of the bands red, green, and blue and display as a color image. Any of the spectral bands may be mapped to any of the colors red, green, or blue, but there are certain common mappings. For this image the blue spectral band was mapped to blue in the image, the red spectral band was mapped to green in the image and near infrared was mapped to red in the image.
The landsat image data may be manipulated in a variety of ways to extract information and bring out details. Some more information on basic techniques is available, along with some raw image data.
The infrared band used is one in which vegetation has a strong peak in its reflectance, so vegetation shows up red in this view. This combination closely approximates color infrared film which has been used for many years.
To the left of the Chesapeake Bay is the Eastern Shore. The many large plowed fields give this region a lighter color in this image. The bright blue-white area in the lower right of the image is clouds.
Two major cities, Baltimore and Washington D.C. show up as the large blue/gray areas. Together they help delineate an interesting geographic feature. Many major east coast cities are located somewhat inland, on large rivers, as far upstream as they may be navigated, bringing them as close as possible to inland products. The limits of navigation were marked by rapids or waterfalls where the rivers flowed from the piedmont to the coastal planes. Connecting these limits on the various rivers gives what is known as the fall line. The fall line is especially obvious just up the Potomac from D.C. at Great Falls.
The Chesapeake Bay, the largest estuary in the U.S. There is only one bridge completely across this bay, it is the Bay Bridge and is located at the narrow region just over half way up this image.
The mountains in the upper left corner of this image are the Catoctins. Beyond them to the left is a little bit of the Great Valley (Cumberland Valley).
All image processing for this page was done using the IDL computer language.