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Monday, August 27, 2007

The Nile Delta

The MERIS instrument flown onboard Envisat is particularly adapted to highlighting visible processes such as sediment input from rivers and the distribution of river sediment by marine coastal processes.

A single acquisition over the Nile Delta made using the MERIS instrument reveals the striking contrast between the pale sands of the Sahara and the bright green of the course of the Nile and its delta, in the simulated true-colour image at left.

At right, bands 15, 13, and 2 have been used to bring out the extent of the Nile plume as sediment is carried from the river into the Eastern Mediterranean. Band 2 highlights surface sediment; bands 15 and 13, in the near-infrared, highlight the difference over land.

Once a seasonal phenomenon, the Nile flood, up to 1965 when the Aswan High Dam became fully operational, provided massive amounts of silt to the delta and the Eastern mediterranean, renewing soil fertility and providing nutrients on which shrimp and phytoplankton populations, thus fisheries, thrived. Today the sediment plume, negligeable when compared with the approximately 100 million metric tonnes of sediment retained behind the Aswan High Dam, is present year-round. It issues both from the Nile and from the Suez, as is clear in the MERIS image at right above.

see the following gallery and search for Nile Delta

Nile Delta photos from satellite

Another image shows that by enhancing a particular part of the data it is possible to render visible the processes which transport Nile and Red Sea sediment along the coast. Here, data in band 7 has been further stretched to show the sedimentation processes along the coast. Representing perhaps finer sediment, a visible blue plume farther north, which can also be seen in the 15, 13, 2 image, is probably a result of sediment being carried out by the river itself.

These images of the Nile Delta were acquired on March 1st, 2003.

A full description of the capabilities of the MERIS instrument can be found in the MERIS Product Handbook. Other images from ENVISAT's first year in orbit are available in the Envisat Image Gallery.