This image of irrigated agriculture in the deserts of central Saudi Arabia, 450 km west of Riyadh, was taken by the Landsat 7 satellite on February 5, 2000, while orbiting 700 km above the surface of the Earth at a speed of roughly 26,000 km/h. The Saudis manage to make the desert bloom by pumping fossil water from deep below the Earth’s surface. A well at the center of each of these fields feeds a center pivot irrigation system which spreads water in large circles up to one kilometer in diameter. The aquifers which supply these fields are ancient and finite. When the fossil water runs out, the desert sands will return. Like the irrigation projects of many arid regions, the Saudis’ desert jewels will soon fade.
I began building this image by selecting a set of infrared bands that would best tell the story of irrigated agriculture in Saudi Arabia. Landsat satellites see the earth through eight spectral bands—the reds, greens, and blues of human experience, along with much longer wavelengths of infrared and thermal light. After using image processing software to assemble the initial false color composite, I selected a 100km-wide subset and choose contrast and saturation levels to accentuate the most interesting features of the image. Because healthy vegetation reflects strongly in the near infrared, the Saudis’ alfalfa and wheat fields are painted red against the desert background. To an astronaut these fields would appear green, and the intense brightness of the desert would likely washout the complex mineralogical patterns picked up by Landsat.
Aside from providing beautiful images, Landsat is used in desert environments to build maps of irrigated agriculture, to prospect for water and minerals, and to manage natural resources. The workhorse of NASA’s Earth observing satellite constellation, Landsat-series satellites have been on orbit continuously since 1972, making Landsat the longest-running satellite collection program in the world.