File:Irrigation in the Heart of the Sahara.jpg
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[編輯]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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來源 | 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 |
拍攝地點 | 22° 16′ 42″ 北, 28° 45′ 44″ 東 ![]() | 位於此地的本圖片與其他圖片: OpenStreetMap | ![]() |
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[編輯]Public domainPublic domainfalsefalse |
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本作品由NASA創作,屬於公有領域。根據NASA的版權政策:“NASA的創作除非另有聲明否則不受版權保護。”(參見:Template:PD-USGov/zh,NASA版權政策或JPL圖像使用政策) | ![]() |
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日期/時間 | 縮圖 | 尺寸 | 使用者 | 備註 | |
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目前 | 2019年9月26日 (四) 01:02 | ![]() | 538 × 403(100 KB) | Gretarsson(留言 | 貢獻) | 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 | 貢獻) | removed border | |
2005年10月4日 (二) 21:22 | ![]() | 540 × 405(33 KB) | David.Monniaux(留言 | 貢獻) | 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 | 貢獻) | 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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方位 | 標準 |
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水平解析度 | 72 dpi |
垂直解析度 | 72 dpi |
使用軟體 | Adobe Photoshop CS Windows |
檔案修改日期時間 | 2019年9月26日 (四) 03:00 |
色彩空間 | sRGB |
影像寬度 | 538 px |
影像高度 | 403 px |
數位化的日期時間 | 2019年9月26日 (四) 04:00 |
詮釋資料最後修改日期 | 2019年9月26日 (四) 04:00 |