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» Elburz Mountains, Iran
 

These images show the vicinity of the Elburz Mountains in northern Iran. Tehran lies in the south, and the Caspian Sea is to the north.

The Elburz Mountains run parallel to the southern coast of the Caspian Sea, and these mountains act as a barrier to rain clouds moving southward; as the clouds rise in altitude to cross the mountains they drop their moisture. This abundant rainfall supports a heavy rainforest (the bright red area) on the northern slopes. The valley to the south receives little precipitation because of this rain-shadow effect of the mountains.

Map of the featured area.

Irrigated agriculture in the valley, shown by the red field patterns, has increased. This agriculture depends on rainfall captured in the mountains and channeled to the valley floor, as well as nearby rivers and drilled wells.

In the lower right of the main images is Tehran, the capital and largest city in Iran. The plain Tehran lies in is like a bowl. High mountains are to the north, and the hills of Kahrizak are to the south. Tehran is far from any major river and relies on water supplies located at a distance from the city. In this series of images, the expansion of the city extends in all directions, especially north toward the mountains. Tehran’s population in 1986 was about 6 million. It has grown to almost 13.7 million in 2016.

Look at the zoomed in images by the coast. Can you tell the peaks (that is, the ridges) from the valleys? It may seem easy, but you may be tricked by a common optical illusion in satellite images called relief inversion.

All Landsat images are designed to be morning views, so all of these images were taken in the morning. The Sun is to the east and south, so these images are lit from below and to the right. This causes the western and northwestern slopes to appear dark because they face the sun less squarely, and so are less illuminated.

However, we unconsciously expect to see images lit from above. This tricks the brain into believing that mountains are valleys or that craters are mountains. If you look at the image upside-down, with the sun angle generally from the top of the image, you will probably see the image differently.

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