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 per hour. The Saudis manage to make the desert bloom by pumping ancient water from as far as a kilometer 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 three kilometers in diameter. When the fossil water runs out, the desert sands will return. Like the irrigation projects of many arid regions, the Saudis’desert jewels are already starting to fade.
You may be asking yourself why the fields appear red? Landsat satellites offer us a much wider palette than the reds, greens, and blues of ordinary human vision (8-11 bands). Here we substitute near infrared signals from Landsat for the ordinary reds we would see if we were on orbit. The resulting image accentuates healthy vegetation as bright red jewels against a darker, mineral-rich desert backdrop. Healthy plants reflect strongly in the near infrared as a protective mechanism to keep from overheating, while photosynthesis means that they absorb strongly in the visible bands. This strong signature, known as the ‘red edge‘ is a key to allowing us to build a clear picture of both plant health and maturity.