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Map of Center-Pivot Irrigation Systems in Nebraska, 1987. Each dot, representing a center-pivot irrigation system, is shown on the map as occupying one quarter-section. The actual area irrigated by a system averages 133 acres. The sizes of such systems vary, however, from less than 50 acres to more than 500 acres. The location of these systems is interpreted from satellite imagery. The Landsat 5 satellite orbits the earth at an altitude of 705 kilometers (438 miles) and resurveys the same point in Nebraska every 16 days. Imagery is purchased from EOSAT through the Earth Resources Observation Systems (EROS) Data Center in Sioux Falls, South Dakota. The pivots portrayed on the map as newly observed include those seen for the first time during the 1987 sruvey. The previously observed category includes those that were noted during earlier annual surveys and that were still apparent during the 1987 inventory. No attempt was made to distinguish between active and inactive pivots in 1987. The Sand Hills region is represented by the gray area, which is provided for those with a specific interest in irrigation development in that area. The inventory of center-pivot irrigation systems in Nebraska by satellite imagery includes a continuing verification process with an annual update that may revise previously published information. The annual totals given on this map represent the latest verified data. Through remote sensing techniques, researchers observe the growth of center-pivot irrigation and assess land-use change. Such procedures are useful in evaluating the effect of irrigation on energy, fertilizer requirements, and water quantity and quality. Project leader: Donald C. Rundquist; project researcher: Allen E. Cook.

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