Northern Saudi Arabia is home to some of the harshest sand and gravel deserts in the world. However, modern agriculture has given this harsh environment a new face. Since the late Eighties, the Saudi government has used oil revenue to develop agricultural fields in the Wadi As-Sirhan Basin in Northern Saudi Arabia. The crops grown in this area include fruits, vegetables, and wheat.For a sense of scale, the circular agricultural fields in use are about 1 kilometer in diameter. The crops are irrigated by water that in part was trapped during the last ice age. Saudi Arabia reaches these underground rivers and lakes by drilling through the desert floor and directly irrigating the fields with center-pivot irrigation. Because rainfall in this area is only about one inch per year, water here is considered a non-renewable resource. Although no one is for certain how much water is beneath the Wadi As-Sirhan Basin, hydrologists estimate it will only be economical to pump for the next 50 years.
Normalized Difference Vegetation Indev or NDVI is a vegetation index that measures wavelengths of light absorbed and reflected by green plants. Certain pigments in plant leaves strongly absorb wavelengths of visible (red) light. The leaves themselves strongly reflect wavelengths of near-infrared light, which is invisble to human eyes. These reflectance properties change with the seasons. A vegetation index is an indicator that describes the greeness, or the relative density and health of vegetation. NDVI uses a mathematical equation to range values from +1.0 to -1.0. Areas of barren rock, sand, or snow usually show very low NDVI values like 0.1 or less, where as dense vegetation such tends to be bright colors and range from 0.6 to 0.9.
In image above, NDVI has been applied to Wadi As-Sirhan agricultural field in northern Saudi Arabia. Within the image, active vegetation appears as a bright color, while dark colors are non-active vegetation or sand, barren rock, or gravel.
- Pryzborski, Paul, Agricultural Fields, Wadi As-Sirhan Basin, Saui Arabia, Earth Observatory, National Aeronautics and Space Administration, March 5, 2012
- United States Geological Survey, NDVI, the Foundation for Remote Sensing Phenology, January 12, 2015