File:Irrigation in the Heart of the Sahara.jpg
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Irrigation_in_the_Heart_of_the_Sahara.jpg (538 × 403像素,文件大小:100 KB,MIME类型:image/jpeg)
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[编辑]描述Irrigation in the Heart of the Sahara.jpg |
Español: Vista aérea de un sistema de riego con pivote central.
English: Irrigation in the Heart of the Sahara (Egypt) Although it is now the largest desert on Earth, during the last ice age the Sahara was a savannah with a climate similar to that of present-day Kenya and Tanzania. The annual rainfall was much greater than it is now, creating many rivers and lakes that are now hidden under shifting sands or exposed as barren salt flats. Over several hundred thousand years the rains also filled a series of vast underground aquifers. Modern African nations are now mining this fossil water to support irrigated farming projects. The above pair of images shows a small settlement just north of the border between Egypt and Sudan. The dark circles—each about a kilometer across—indicate central-pivot irrigation. A well drilled in the center of each circle supplies water to a rotating series of sprinklers. Rainfall in this area of the Sahara is only a few centimeters a year, so the aquifers will take thousands of years (or longer) to recharge, making the water a non-renewable resource. Although no one knows how much water is beneath the Sahara, hydrologists estimate that it will only be economical to pump water for fifty years or so. On the other hand, alternative technologies for providing fresh water in this arid region—primarily desalinization—are too expensive for widespread use. Sudan, Libya, Chad, Tunisia, Morocco and Algeria are some of the other Saharan nations irrigating with fossil water, but the practice is not limited to Africa. In the southern plains of the United States, the Ogallala aquifer is being drained faster than it can be replenished. These true-color images were acquired by the Enhanced Thematic Mapper plus (ETM+) aboard NASA’s Landsat 7 satellite. The Landsat satellites enable scientists to monitor land use and land cover change dating back to 1972. Landsat 7 is designed to last until at least 2004, and follow-on missions are currently being planned. |
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来源 | Cropped from: https://visibleearth.nasa.gov/view.php?id=57868 |
作者 | Images and animation by Robert Simmon, based on data aqcuired by the Landsat 7 Science Team Landsat data is archived and distributed by the USGS EROS Data Center |
相机位置 | 22° 16′ 42″ 北, 28° 45′ 44″ 东 | 在以下服务上查看本图像和附近其他图像: OpenStreetMap | 22.278333; 28.762222 |
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[编辑]Public domainPublic domainfalsefalse |
本文件完全由NASA创作,在美国属于公有领域。根据NASA的版权方针,NASA的材料除非另有声明否则不受版权保护。(参见Template:PD-USGov/zh、NASA版权方针页面或JPL图片使用方针。) | ||
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日期/时间 | 缩略图 | 大小 | 用户 | 备注 | |
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当前 | 2019年9月26日 (四) 01:02 | 538 × 403(100 KB) | Gretarsson(留言 | 贡献) | scale bar added (length according to scale bar in original, uncropped version) -- its always a bad idea to remove a scale bar from a satellite image or map... | |
2010年12月18日 (六) 22:57 | 538 × 403(41 KB) | WikiMichi(留言 | 贡献) | removed border | ||
2005年10月4日 (二) 21:22 | 540 × 405(33 KB) | David.Monniaux(留言 | 贡献) | Irrigation in the Heart of the Sahara (Egypt) Source: [http://visibleearth.nasa.gov/cgi-bin/viewrecord?12100 NASA] Caption of source site, including animation: Credit: Images and animation by Robert Simmon, based on data aqcuired by the La | ||
2005年10月4日 (二) 21:18 | 540 × 899(61 KB) | David.Monniaux(留言 | 贡献) | Irrigation in the Heart of the Sahara (Egypt) Source: [http://visibleearth.nasa.gov/cgi-bin/viewrecord?12100 NASA] Caption of source site, including animation: Credit: Images and animation by Robert Simmon, based on data aqcuired by the La |
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方向 | 正常 |
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水平分辨率 | 72 dpi |
垂直分辨率 | 72 dpi |
使用软件 | Adobe Photoshop CS Windows |
文件修改日期时间 | 2019年9月26日 (四) 03:00 |
色彩空间 | sRGB |
图像宽度 | 538 px |
图像高度 | 403 px |
数字化日期时间 | 2019年9月26日 (四) 04:00 |
元数据最后修改日期 | 2019年9月26日 (四) 04:00 |