What's lies beneath the Sahara?

Antaletriangle · 09-16-2008, 07:48 PM

http://www.v-j-enterprises.com/nile.html

SUMMARY: During the last Ice Age, the Sahara was savannah with rivers, lakes and plentiful rains. Over the past 10,000 years that landscape changed, but the rains from that period progressively percolated beneath the ground to be collected in aquifers. Today these aquifers are an important source of water for irrigating agriculture and supporting human populations in the area.

The European Space Agency (ESA) has launched a program to monitor the management of this non-renewable resource. Overexploitation risks exhaustion and saline contamination of groundwater, putting the whole region at risk.

A release detailing ESA's work can be found below.

http://news.mongabay.com/2005/1219-esa.html

"Discovery of crater indicates meteorite impact in Sahara"
(Several impact craters litter the Sahara desert,vitrified rock that is now exposed from sand blasting from desert storms-could this possibly have been something else and could it have wiped out Atlantis?)
Researchers from Boston University have discovered the remnants of the largest crater of the Great Sahara of North Africa, which may have been formed by a meteorite impact tens of millions of years ago. Dr. Farouk El-Baz made the discovery while studying satellite images of the Western Desert of Egypt with his colleague, Dr. Eman Ghoneim, at BU's Center for Remote Sensing.
The double-ringed crater – which has an outer rim surrounding an inner ring – is approximately 31 kilometers in diameter. Prior to the latest finding, the Sahara's biggest known crater, in Chad, measured just over 12 kilometers. According to El-Baz, the Center's director, the crater's vast area suggests the location may have been hit by a meteorite the entire size of the famous Meteor (Barringer) Crater in Arizona which is 1.2 kilometers wide.

El-Baz named his find "Kebira," which means "large" in Arabic and also relates to the crater's physical location on the northern tip of the Gilf Kebir region in southwestern Egypt. The reason why a crater this big had never been found before is something the scientists are speculating.

"Kebira may have escaped recognition because it is so large – bigger than the area of 125 football fields, or the total expanse of the Cairo urban region from its airport in the northeast to the Pyramids of Giza in the southwest," said Dr. El-Baz. "Also, the search for craters typically concentrates on small features, especially those that can be identified on the ground. The advantage of a view from space is that it allows us to see regional patterns and the big picture."

The researchers also found evidence that Kebira suffered significant water and wind erosion which may have helped keep its features unrecognizable to others. "The courses of two ancient rivers run through it from the east and west," added Ghoneim.

The terrain in which the crater resides is composed of 100 million year-old sandstone – the same material that lies under much of the eastern Sahara. The researchers hope that field investigations and samples of the host rock will help in determining the exact age of the crater and its surroundings.

Kebira's shape is reminiscent of the many double-ringed craters on the Moon, which Dr. El-Baz remembers from his years of work with the Apollo program. Because of this, he believes the crater will figure prominently in future research in comparative planetology. And, since its shape points to an origin of extraterrestrial impact, it will likely prove to be the event responsible for the extensive field of "Desert Glass" – yellow-green silica glass fragments found on the desert surface between the giant dunes of the Great Sand Sea in southwestern Egypt.
Satellite imagery shows that the Nile used to flow into the Atlantic way back-could there lie under the shifting sands of the Sahara an ancient civilisation that once flourished;a potential 'Atlantis'?
http://www.africanconservation.org/c...um=DCForumID33

One of the many great mysteries of the Nile river may be solved with the discovery of an ancient river channel buried under layers of sand in the Sahara Desert in Africa.

The buried river channel was revealed in images taken by the Spaceborne Imaging Radar C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The radar images were processed at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, and the University of Texas at Dallas (UTD).

"One of the things this discovery helps us examine is the origin of what's called the Great Bend of the Nile," said Dr. Bob Stern, a SIR-C science team member at UTD. "The Nile generally flows due north, but in the Sudan, it makes a huge, looping bend that is really remarkable because the river is flowing through the Sahara Desert, the largest, driest desert on the face of the Earth. There must be a very good reason for the river to make this great bend, otherwise we would expect it to flow straight to the Mediterranean Sea." Instead, it bends southwestwards and wanders through the Sahara for another 200 miles before resuming its northward course.

"The discovery of the river channel shows us that probably sometime between 10,000 and 1,000,000 years ago, the Nile was forced to abandon its bed and take up a new course to the south. This buried channel proves that this region has been tectonically active and shows us how this activity has forced the river to change its course," Stern said. "Understanding what controls the course of the Nile is a critical part of understanding Nile history and predicting Nile behavior, which is important because the river is essential to millions of people in Egypt, Sudan, and Ethiopia."
http://findarticles.com/p/articles/m.../ai_2124338163

An international team worked on the verge of the Sahara to gather data on the ground and in the air, to be compared with imagery of the same region acquired by ESA satellites. The results will be used in support of an ambitious project to apply satellite remote sensing to improve monitoring and management of vast water aquifers concealed beneath the desert.

High-resolution radar as well as hyperspectral optical imagery was acquired during flights across two test areas in southern Tunisia. Meanwhile ground teams precisely documented ground vegetation and terrain at sampling sites within these test areas, with samples taken to local laboratories for detailed analysis. And ESA's Envisat, ERS-2 and Proba satellites acquired images of these sites around the same time. The aim was to scale up the findings from the ground, and at the same time to use this 'ground truth' to calibrate satellite imagery with reality on the sandy arid ground – as well as seeing what can be learnt about the water beneath it.

The Sahara has altered through the ages: during the last Ice Age, 10 000 years ago, there was savannah here with rivers, lakes and plentiful rains. That landscape has vanished now, but the rains from that period progressively percolated beneath the ground to be collected in layers of water-bearing rock known as aquifers.

This 'fossil water' is today used in North African nations for irrigating agriculture and to support population growth. It is a valuable resource but also a non-renewable one - distributed across national boundaries - which requires careful management to be employed in a sustainable way. Over-exploitation risks exhaustion of groundwater, plus loss of artesian pressure to put remaining supplies out of reach or induce contamination from nearby saline water deposits.

This satellite image of the northern part of the Ben Gardane study area was acquired by the hyperspectral CHRIS image on ESA's Proba microsatellite during the AquiferEx campaign in Tunisia. It includes 'red edge' combinations of spectral bands sensitive to chlorophyll in healthy vegetation.
Credits: ESA
Working with partners including African water agencies, ESA has commenced a project called Aquifer to develop satellite-derived products and services to support the sustainable management of ground water. Planned products include land-use and land-cover maps, change maps, surface water extent and dynamics, digital terrain models and estimates of water consumption and extraction. These required products were identified by the involved water agencies, in Tunisia specifically the Direction Générale des Ressources en Eau (DGRE) under the Ministère de l'Agriculture.

Aquifer takes place within the framework of the TIGER Initiative, aimed at applying Earth Observation technology to improve availability and management of water resources, with a particular focus on Africa.

Both sites are located above the vast North-Western Sahara Aquifer System (better known in French as the Systeme d'Aquiferes du Sahara Septentrional or SASS) and the interconnected Djeffara aquifer on its northern boundary, which stretches across 1 000 000 square kilometres of Algerian, Libyan and Tunisian territory and is one of the working areas of the Aquifer project.

The two sites have significant differences: Ben Gardane to the south suffers from wind erosion and its groundwater is undergoing salinization due to invading sea water. Gabes further north includes several oases and ground water at various levels, but its deep-level fossil water has been exhausted in many places.

A Dornier Do-228 aircraft flown by the German Aerospace Center (DLR) was the platform for two airborne sensors operating simultaneously: the Experimental Synthetic Aperture Radar (E-SAR) built by DLR, which can acquire imagery at differing radar wavelengths and polarisations, and the Airborne Visible Imaging and Infrared Imaging Spectrometer (AVIS), built by the University of Munich, which gathers additional environmental and vegetation information by observing across dozens of spectral bands invisible to the human eye.

"The hyperspectral and radar data of AquiferEx will allow refined land use and land cover mapping," explained Aquifer Project Manager Stefan Saradeth, of Munich-based GAF AG. "From there it is planned to derive improved estimates of water consumption in agriculturally-utilised areas. AquiferEx also provides a baseline dataset for the validation of other Aquifer results, and the hyperspectral and radar data will be used to develop a range of science products, demonstrating future development lines and showing the potential of new sensors."

At the same time as the Dornier was flying out of Tunisia's Djerba International Airport, Tunisian and European participants on the ground gathered information including the size and position of fields, local topography, the soil surface characteristics and vegetation type, distribution and parameters such as leaf area index and wet and dry biomass. Measurements had to be as authoritative as possible, for example close-up three-dimensional photographs were taken of plant rows and soil roughness while sap flow measurements made for olive trees. Samples were analysed in Tunisian laboratories and weather conditions were also documented.

"The conditions for the ground teams were a lot rougher," said Rolf Scheiber of DLR, who manages the AquiferEx project. "The southern test site of Ben Gardane is a pretty remote place and it took the ground team quite some time to reach it. The accessibility within the site was also restricted… even using four wheel drive cars, the northern part of the site could not be reached due to shallow water obstacles. In general, without the cooperation and help of local institutions like the Commissariat Régional au Développement Agricole (CRDA) in Gabes and Medenine and the Institut des Régions Arides (IRA) in Medenine providing guiding experts and lab facilities the performance of ground measurements would have been very limited."

09-16-2008, 07:48 PM	#1
Antaletriangle Avalon Senior Member Join Date: Sep 2008 Location: U.K. Posts: 3,380	What's lies beneath the Sahara? http://www.v-j-enterprises.com/nile.html SUMMARY: During the last Ice Age, the Sahara was savannah with rivers, lakes and plentiful rains. Over the past 10,000 years that landscape changed, but the rains from that period progressively percolated beneath the ground to be collected in aquifers. Today these aquifers are an important source of water for irrigating agriculture and supporting human populations in the area. The European Space Agency (ESA) has launched a program to monitor the management of this non-renewable resource. Overexploitation risks exhaustion and saline contamination of groundwater, putting the whole region at risk. A release detailing ESA's work can be found below. http://news.mongabay.com/2005/1219-esa.html "Discovery of crater indicates meteorite impact in Sahara" (Several impact craters litter the Sahara desert,vitrified rock that is now exposed from sand blasting from desert storms-could this possibly have been something else and could it have wiped out Atlantis?) Researchers from Boston University have discovered the remnants of the largest crater of the Great Sahara of North Africa, which may have been formed by a meteorite impact tens of millions of years ago. Dr. Farouk El-Baz made the discovery while studying satellite images of the Western Desert of Egypt with his colleague, Dr. Eman Ghoneim, at BU's Center for Remote Sensing. The double-ringed crater – which has an outer rim surrounding an inner ring – is approximately 31 kilometers in diameter. Prior to the latest finding, the Sahara's biggest known crater, in Chad, measured just over 12 kilometers. According to El-Baz, the Center's director, the crater's vast area suggests the location may have been hit by a meteorite the entire size of the famous Meteor (Barringer) Crater in Arizona which is 1.2 kilometers wide. El-Baz named his find "Kebira," which means "large" in Arabic and also relates to the crater's physical location on the northern tip of the Gilf Kebir region in southwestern Egypt. The reason why a crater this big had never been found before is something the scientists are speculating. "Kebira may have escaped recognition because it is so large – bigger than the area of 125 football fields, or the total expanse of the Cairo urban region from its airport in the northeast to the Pyramids of Giza in the southwest," said Dr. El-Baz. "Also, the search for craters typically concentrates on small features, especially those that can be identified on the ground. The advantage of a view from space is that it allows us to see regional patterns and the big picture." The researchers also found evidence that Kebira suffered significant water and wind erosion which may have helped keep its features unrecognizable to others. "The courses of two ancient rivers run through it from the east and west," added Ghoneim. The terrain in which the crater resides is composed of 100 million year-old sandstone – the same material that lies under much of the eastern Sahara. The researchers hope that field investigations and samples of the host rock will help in determining the exact age of the crater and its surroundings. Kebira's shape is reminiscent of the many double-ringed craters on the Moon, which Dr. El-Baz remembers from his years of work with the Apollo program. Because of this, he believes the crater will figure prominently in future research in comparative planetology. And, since its shape points to an origin of extraterrestrial impact, it will likely prove to be the event responsible for the extensive field of "Desert Glass" – yellow-green silica glass fragments found on the desert surface between the giant dunes of the Great Sand Sea in southwestern Egypt. Satellite imagery shows that the Nile used to flow into the Atlantic way back-could there lie under the shifting sands of the Sahara an ancient civilisation that once flourished;a potential 'Atlantis'? http://www.africanconservation.org/c...um=DCForumID33 One of the many great mysteries of the Nile river may be solved with the discovery of an ancient river channel buried under layers of sand in the Sahara Desert in Africa. The buried river channel was revealed in images taken by the Spaceborne Imaging Radar C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The radar images were processed at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, and the University of Texas at Dallas (UTD). "One of the things this discovery helps us examine is the origin of what's called the Great Bend of the Nile," said Dr. Bob Stern, a SIR-C science team member at UTD. "The Nile generally flows due north, but in the Sudan, it makes a huge, looping bend that is really remarkable because the river is flowing through the Sahara Desert, the largest, driest desert on the face of the Earth. There must be a very good reason for the river to make this great bend, otherwise we would expect it to flow straight to the Mediterranean Sea." Instead, it bends southwestwards and wanders through the Sahara for another 200 miles before resuming its northward course. "The discovery of the river channel shows us that probably sometime between 10,000 and 1,000,000 years ago, the Nile was forced to abandon its bed and take up a new course to the south. This buried channel proves that this region has been tectonically active and shows us how this activity has forced the river to change its course," Stern said. "Understanding what controls the course of the Nile is a critical part of understanding Nile history and predicting Nile behavior, which is important because the river is essential to millions of people in Egypt, Sudan, and Ethiopia." http://findarticles.com/p/articles/m.../ai_2124338163 An international team worked on the verge of the Sahara to gather data on the ground and in the air, to be compared with imagery of the same region acquired by ESA satellites. The results will be used in support of an ambitious project to apply satellite remote sensing to improve monitoring and management of vast water aquifers concealed beneath the desert. High-resolution radar as well as hyperspectral optical imagery was acquired during flights across two test areas in southern Tunisia. Meanwhile ground teams precisely documented ground vegetation and terrain at sampling sites within these test areas, with samples taken to local laboratories for detailed analysis. And ESA's Envisat, ERS-2 and Proba satellites acquired images of these sites around the same time. The aim was to scale up the findings from the ground, and at the same time to use this 'ground truth' to calibrate satellite imagery with reality on the sandy arid ground – as well as seeing what can be learnt about the water beneath it. The Sahara has altered through the ages: during the last Ice Age, 10 000 years ago, there was savannah here with rivers, lakes and plentiful rains. That landscape has vanished now, but the rains from that period progressively percolated beneath the ground to be collected in layers of water-bearing rock known as aquifers. This 'fossil water' is today used in North African nations for irrigating agriculture and to support population growth. It is a valuable resource but also a non-renewable one - distributed across national boundaries - which requires careful management to be employed in a sustainable way. Over-exploitation risks exhaustion of groundwater, plus loss of artesian pressure to put remaining supplies out of reach or induce contamination from nearby saline water deposits. This satellite image of the northern part of the Ben Gardane study area was acquired by the hyperspectral CHRIS image on ESA's Proba microsatellite during the AquiferEx campaign in Tunisia. It includes 'red edge' combinations of spectral bands sensitive to chlorophyll in healthy vegetation. Credits: ESA Working with partners including African water agencies, ESA has commenced a project called Aquifer to develop satellite-derived products and services to support the sustainable management of ground water. Planned products include land-use and land-cover maps, change maps, surface water extent and dynamics, digital terrain models and estimates of water consumption and extraction. These required products were identified by the involved water agencies, in Tunisia specifically the Direction Générale des Ressources en Eau (DGRE) under the Ministère de l'Agriculture. Aquifer takes place within the framework of the TIGER Initiative, aimed at applying Earth Observation technology to improve availability and management of water resources, with a particular focus on Africa. Both sites are located above the vast North-Western Sahara Aquifer System (better known in French as the Systeme d'Aquiferes du Sahara Septentrional or SASS) and the interconnected Djeffara aquifer on its northern boundary, which stretches across 1 000 000 square kilometres of Algerian, Libyan and Tunisian territory and is one of the working areas of the Aquifer project. The two sites have significant differences: Ben Gardane to the south suffers from wind erosion and its groundwater is undergoing salinization due to invading sea water. Gabes further north includes several oases and ground water at various levels, but its deep-level fossil water has been exhausted in many places. A Dornier Do-228 aircraft flown by the German Aerospace Center (DLR) was the platform for two airborne sensors operating simultaneously: the Experimental Synthetic Aperture Radar (E-SAR) built by DLR, which can acquire imagery at differing radar wavelengths and polarisations, and the Airborne Visible Imaging and Infrared Imaging Spectrometer (AVIS), built by the University of Munich, which gathers additional environmental and vegetation information by observing across dozens of spectral bands invisible to the human eye. "The hyperspectral and radar data of AquiferEx will allow refined land use and land cover mapping," explained Aquifer Project Manager Stefan Saradeth, of Munich-based GAF AG. "From there it is planned to derive improved estimates of water consumption in agriculturally-utilised areas. AquiferEx also provides a baseline dataset for the validation of other Aquifer results, and the hyperspectral and radar data will be used to develop a range of science products, demonstrating future development lines and showing the potential of new sensors." At the same time as the Dornier was flying out of Tunisia's Djerba International Airport, Tunisian and European participants on the ground gathered information including the size and position of fields, local topography, the soil surface characteristics and vegetation type, distribution and parameters such as leaf area index and wet and dry biomass. Measurements had to be as authoritative as possible, for example close-up three-dimensional photographs were taken of plant rows and soil roughness while sap flow measurements made for olive trees. Samples were analysed in Tunisian laboratories and weather conditions were also documented. "The conditions for the ground teams were a lot rougher," said Rolf Scheiber of DLR, who manages the AquiferEx project. "The southern test site of Ben Gardane is a pretty remote place and it took the ground team quite some time to reach it. The accessibility within the site was also restricted… even using four wheel drive cars, the northern part of the site could not be reached due to shallow water obstacles. In general, without the cooperation and help of local institutions like the Commissariat Régional au Développement Agricole (CRDA) in Gabes and Medenine and the Institut des Régions Arides (IRA) in Medenine providing guiding experts and lab facilities the performance of ground measurements would have been very limited."