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It should be recognized that, depending on the intended application, 
useful products, either analog or digital, can emerge from any of the 
four processing steps and that the sequence of processing is flexible; 
step 4 for example may follow either steps 1, 2, or 3. 
Details of these processing procedures are well summarized by 
Bernstein and Ferneyhough (1975). 
Although Landsat is not designed to be a stereoscopic system, 
examples of stereoscopic coverage can be found in the higher latitudes 
of Arctic and sub-Arctic regions. Orbit shifts have also provided 
examples in some of the middle latitude regions. U.S. Geological Survey 
(USGS) personnel at Flagstaff, Arizona, have produced a computer- 
generated stereo pair from a single Landsat-1 image of the Gunnison 
River area, Colorado.  Parallactic displacement commensurate with ter- 
rain relief was introduced by manipulating each picture element in 
accordance with digital terrain elevation data obtained from existing 
1:250,000-scale topographic maps (Batson and Bliason, 1975). This 
recreated scene, containing parallax, is used as a stereo mate to the 
standard Landsat image. The Gunnison River stereo pair has been 
reproduced in black-and-white, color, and color infrared. 
Without question, the successful operation of Landsat-1 and -2 has 
been one of the outstanding developments in the field of remote sensing. 
More than 300 formal Landsat-1 experiments, many by foreign nationals, 
were performed with the data. The experiments spanned all components 
of the earth sciences; copies of intermediate and final reports showing 
the results of these experiments may be obtained from the National 
Technical Information Service (NTIS), Department of Commerce, 5285 Port 
Royal Road, Springfield, Virginia 22161. Reports available through 
Oct. 15, 1975, and their NTIS numbers are given in Bidwell and Mitchell 
(1975). Additional experiments are now underway as a part of the 
Landsat-2 program. Because Landsat data are essentially global in 
coverage, readily available to any citizen of the world, and are quite 
inexpensive, the use of the data has gone far beyond use in formal 
experiments and is increasing. Table 1 (DeNoyer, 1976) summarizes the 
growth in purchases of Landsat and other remote-sensing data from the 
EROS (Earth Resources Observation Systems Program) Data Center (EDC), 
located in Sioux Falls, S. Dakota, U.S.A.