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Earth from Space: Ouarkziz Impact Crater

Jonathan Nally — Thu, 17 May 2012 13:01:50 +0000

Satellite image of the Ouarkziz Impact Crater in Algeria.

THE OUARKZIZ IMPACT CRATER is located in northwestern Algeria, close to the border with Morocco. The crater was formed by a meteor impact less than 70 million years ago, during the late Cretaceous Period of the Mesozoic Era, or “Age of Dinosaurs.”

Originally called Tindouf, the 3.5-kilometre wide crater has been heavily eroded since its formation; however, its circular shape is highlighted by exposures of older sedimentary rock layers that form ridgelines trending roughly northwest to southeast. From the vantage point of an astronaut on the International Space Station, the impact crater is clearly visible with a magnifying camera lens.

A geologist interpreting this image to build a geological history of the region would conclude that the Ouarkziz crater is younger than the sedimentary rocks, as the rock layers had to be already present for the meteor to hit them. Likewise, a stream channel can be seen cutting across the centre of the crater, indicating that the channel formed after the impact had occurred. This Principal of Cross-Cutting Relationships, usually attributed to the 19th century geologist Charles Lyell, is a basic logic tool used by geologists to build relative sequence and history of events when investigating a region.

A closer view of the Ouarkziz Impact Crater, clearly showing where a stream has broken through its rim.

Astronaut photograph provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Centre. The image was taken by the Expedition 30 crew. Text adapted from information issued by William L. Stefanov, Jacobs/ESCG at NASA-JSC.

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Australia from Space – Outback fires

Jonathan Nally — Tue, 15 May 2012 14:00:53 +0000

NASA's Aqua satellite took this image showing dozens of fires scattered across the Kimberley region of Western Australia in early May. The red colours are markers of the locations of the fires, not actually visible flames.

WHEN THIS IMAGE WAS CAPTURED on May 2, 2012, dozens of fires—most likely management fires started by government authorities—were burning in the Kimberley region of Western Australia.

Fire season in this part of Australia usually begins in May and ends in November. Once started, fires can be difficult to control. Much of the vegetation is fire prone, and the terrain is hard to access with the big machines (such as bulldozers) used to extinguish fires.

But since May is only the beginning of the dry season, vegetation is still relatively moist, and fires are relatively easy to contain. Authorities take advantage of this by starting management fires that are designed to remove vegetation that could fuel large wildfires later in the season.

Because officials are concerned that wildfires are taking a toll on the local tourism industry, they have intensified their efforts to prevent damaging wildfires. As part of this effort, they have begun setting patches of oval-shaped fires rather than burning linear fire breaks as they did in the past, according to an article published by Australian Geographic. The new approach has reduced the overall fire size, and posed fewer threats to animals and plants in the Kimberley region.

The image above was acquired at 12:20pm local time on May 2 by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’s Aqua satellite. Fires continued to burn nearby over the following days, although clouds moved in around May 6, 2012. The LANCE MODIS Rapid Response system provides twice daily images of northwestern Australia.

NASA image by Jeff Schmaltz, LANCE MODIS Rapid Response. Text adapted from information issued by caption by Adam Voiland and Michon Scott, NASA Earth Observatory.

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Earth from Space: Sideways view of Antarctica

Jonathan Nally — Wed, 11 Jan 2012 13:01:41 +0000

An astronaut aboard the International Space Station took this photo at a highly oblique angle. It shows a small part of the Antarctic coastline.

THE INCLINED EQUATORIAL ORBIT of the International Space Station (ISS) limits astronauts to nadir views of Earth—looking straight down from the spacecraft—between approximately 52 degrees North latitude and 52 degrees South.

However, when viewing conditions are ideal, the crew can obtain detailed oblique images—looking outwards at an angle—of features at higher latitudes, such as Greenland or, in this image, Antarctica.

While the bulk of the continent of Antarctica sits over the South Pole, the narrow Antarctic Peninsula extends like a finger towards the tip of South America. The northernmost part of the Peninsula is known as Graham Land, a small portion of which (located at approximately 64 degrees South latitude) is visible at the top left in this astronaut photograph.

Off the coast of Graham Land to the north-northwest, two of the South Shetland Islands—Livingston Island and Deception Island—are visible. Both have volcanic origins, and active volcanism at Deception Island has been recorded since 1800. (The last verified eruptive activity occurred in 1970.)

Closer to the coastline of Graham Land, Brabant Island (not part of the South Shetlands) also includes numerous outcrops of volcanic rock, attesting to the complex tectonic history of the region.

The ISS was located over the South Atlantic Ocean, approximately 1,800 kilometres to the northeast when this image was taken. This long viewing distance, combined with the highly oblique angle, accentuates the shadowing of the ground and provides a sense of the topography similar to the view you get from an airplane.

It also causes foreshortening of features in the image, making them appear closer to each other than they actually are. For example, the distance between Livingston and Deception Islands is approximately 20 kilometres.

Astronaut photograph provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Centre. Text adapted from information issued by William L. Stefanov, Jacobs/ESCG at NASA-JSC.

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Earth from Space – Eruption in the Red Sea

Jonathan Nally — Thu, 05 Jan 2012 13:01:23 +0000

NASA Earth Observing-1 (EO-1) satellite image of a volcanic eruption in the Zubair Group of islands in the Red Sea.

AN ERUPTION OCCURRED in the Red Sea in December 2011. According to news reports, fishermen witnessed lava fountains reaching up to 30 metres tall on December 19.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites observed plumes on December 20 and December 22. Meanwhile, the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite detected elevated levels of sulphur dioxide, further indicating an eruption.

The activity in the Red Sea included more than an eruption. By December 23, 2011, what looked like a new island had appeared.

The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured these high-resolution, natural-colour images on December 23, 2011 (above), and October 24, 2007 (below).

A satellite image of the same region, taken in 2007, shows no sign of the new volcanic island.

The image from December 2011 shows an apparent island where there had previously been an unbroken water surface. A thick plume rises from the island, dark near the bottom and light near the top, perhaps a mixture of volcanic ash and water vapour.

The volcanic activity occurred along the Zubair Group, a collection of small islands off the west coast of Yemen. Running in a roughly northwest-southeast line, the islands poke above the sea surface, rising from a shield volcano.

This region is part of the Red Sea Rift where the African and Arabian tectonic plates pull apart and new ocean crust regularly forms.

This wider view shows more of the islands in the Zubair Group.

And this close up gives a better view of the new island and the huge plume of smoke and steam.

NASA Earth Observatory image created by Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 team. Text adapted from information issued by Michon Scott.

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Earth from Space – Cocos (Keeling) Islands

Jonathan Nally — Wed, 04 Jan 2012 13:01:25 +0000

NASA satellite image of the South Keeling Islands, part of the Cocos (Keeling) Islands archipelago in the Indian Ocean between Australia and Sri Lanka.

THE COCOS (KEELING) ISLANDS lie in the eastern Indian Ocean, about 2,900 kilometres northwest of Perth, Western Australia. It is about halfway between Australia and Sri Lanka.

Comprised of coral atolls and islands, the archipelago includes North Keeling Island and the South Keeling Islands. Total human population is about 600.

The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this natural-colour image of South Keeling Islands on July 31, 2009.

Coral atolls—which are largely composed of huge colonies of tiny animals such as cnidaria—form around islands. After the islands sink, the coral remains, generally forming complete or partial rings. Only some parts of South Keeling Islands still stand above the water surface. In the north, the ocean overtops the coral.

Along the southern rim of this coral atoll, the shallow water appears aquamarine. Water darkens to navy blue as it deepens toward the central lagoon. Above the water line, coconut palms and other plants form a thick carpet of vegetation.

In 2005, the Australian government issued a report on the Cocos (Keeling) Islands, summarising field research conducted between 1997 and 2005. It found that hard corals, which play a primary role in reef building, were not the only corals at South Keeling Islands. Soft corals were also thriving at study sites throughout the reef. Although coral and rock predominated, the researchers also found varying amounts of silt, sand, rubble, sponges, and seaweed

Some of the coral had recently died, and coral predators appeared in high densities at some sites. But overall, the report noted, “the coral reef community at Cocos (Keeling) Islands is very healthy and in a stable period, with little impact from anthropogenic activities.”

The Cocos Islands are served by regular Virgin Australia flights, which land on and depart from the single 2,438-metre-long runway shown in the enlargement below:

Close up satellite image of the runway on the Cocos (Keeling) Islands.

For a full-size version of the main image, click here (3MB)

NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team. Text adapted from information issued by Michon Scott.

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Earth from Space – Videos of our World, Pt 2

Jonathan Nally — Thu, 29 Dec 2011 13:01:24 +0000

HERE ARE SOME MORE AMAZING short videos put together from images taken by astronauts aboard the International Space Station.

This first one was made from images taken on December 4, 2011, and shows a pass from just northwest of Morocco to central Kazakhstan. The first thing that can be seen is Spain and Portugal, with Lisbon lit up brightly in the foreground near the Atlantic Ocean and Madrid in the middle of Spain.

The pass continues into France, with the English Channel in the far left and the Italian Peninsula in the far right. Further down the pass and on the left video, the Baltic Sea appears as a dark patch surrounded by light as the ISS continues to the east-northeast towards Moscow, Russia. The pass continues toward central Russia before the sunrise in the east comes up.

This next one was taken November 24, 2011 and shows a pass over the South Pacific Ocean northeast to the North Atlantic Ocean, just east of Newfoundland. The video begins over the dark Pacific Ocean as the ISS travels northeast towards the western coast of Mexico. The bright lights of Mexico City can be seen left of track, along with the lights of Honduras and Guatemala just right of track.

The pass continues over the Yucatan Peninsula, where Cozumel and Merida are visible as brighter spots on the peninsula. As the ISS tracks northeast over the Caribbean Sea, southeastern United States becomes visible, with the Florida Peninsula standing out well. The city lights of the larger cities such as Miami, Tampa, and Orlando light up the peninsula. The pass ends by tracking up the eastern coast of the United States, where Washington D.C., Baltimore, and New York City stand out.

The third video was taken November 18 to 19, 2011, and shows a pass from South Africa, west of Johannesburg, to southern Pakistan. The Russian vehicle Soyuz is shown off-centre throughout the video, just days before astronauts Mike Fossum, Satoshi Furukawa, and Sergey Volkov boarded this vehicle to come back to Earth.

Near the beginning of the video, the bright lights of Johannesburg as displayed as the ISS tracks northeast up the eastern Africa coastline. A few lightning storms can also be seen near Johannesburg. As the pass continues, the Arabian Peninsula is only briefly seen in the far right of the video before the pass ends over the Arabian Sea, just south of Pakistan.

This one was taken on November 16, 2011, on a pass over the Pacific Ocean, from just west of California to just west of Costa Rica and Panama in Central America. The camera in the cupola is facing west-southwest towards North and Central America. The pass begins looking just north of the Baja Peninsula, where Los Angeles and San Diego can carefully be seen near the coast. Continuing down the Baja Peninsula and the Gulf of California, the pass continues looking into Mexico. Finally, as the cloud cover thickens, the pass closes over Central America, looking far west at Costa Rica and Honduras.

Taken on October 15, 2011, this sequence of shots shows a pass from just west of San Francisco, California over the Pacific Ocean to the southern tip of the Hudson Bay. The video begins as the ISS is just west of San Francisco flying northeast. The coastal lights distinguish the land and water here.

The pass continues northeast toward Wyoming and North Dakota, before crossing over into Canada. From here, the Aurora Borealis is seen, with an interesting looking angle from underneath the lights. A blanket of clouds covers Manitoba and Ontario as the ISS tracks closer to the Northern Lights.

This video was taken on December 4, 2011,, on a pass from just northwest of Morocco to central Kazakhstan. The first thing that can be seen is Spain and Portugal, with Lisbon lit up brightly in the foreground near the Atlantic Ocean and Madrid in the middle of Spain.

The next video was taken on October 20, 2011, on a descending pass from eastern China to western New Guinea, and rounds out to an ascending pass just as the video ends north of Australia. As the pass begins southeastward towards the South China Sea, the first noticeably-lit area is that of Hong Kong and Macau. The island of Taiwan can also be easily seen left of track.

The ISS passes over the South China Sea towards the Philippines, which have some cloud cover and storms. Finally, the pass ends just north of Australia, where the Yorke Peninsula can be seen as a dark, rusty colour protruding into the water.

And this final video was taken on October 22, 2011, on a pass from the North Atlantic Ocean, just west of Portugal and Spain, to northwest of Mozambique in southeastern Africa. This video begins just northwest of the United Kingdom and shows the ISS travelling southeast towards Africa. The camera points at the sky, capturing clusters of stars as they seem to fly by.

Videos courtesy NASA and the Image Science and Analysis Laboratory, NASA-Johnson Space Centre.

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Australia from Space: Part 5

Jonathan Nally — Sun, 11 Dec 2011 13:01:35 +0000

IT’S DIFFICULT TO GET A TRUE PICTURE of the scale of Australia’s Red Centre from the ground, but satellite images help us to comprehend the breadth and beauty of the region. These remarkable images were taken by the Proba, Envisat and Landsat satellites, and show two of Australia’s most famous landmarks—Uluru and Lake Eyre.

The rock formation Uluru, also known as Ayers Rock, as seen by the European Proba satellite. Uluru is the world's largest monolith, and a sacred site to Australia's indigenous peoples. It is 3.6 km long and two km wide. The walk around it covers 9.4 km.

This black and white Proba image gives us a closer view of Uluru, and shows the layers of rock titled towards the vertical.

This Envisat image highlights the Lake Eyre Basin, one of the world’s largest internally draining systems, in the heart of Australia. White cloud streaks stand in contrast to the Red Centre’s vast amounts of crimson soil and sparse greenery. The basin covers about 1.2 million sq km (about the size of France, Germany and Italy combined), including large portions of South Australia (bottom), the Northern Territory (upper left) and Queensland (upper right) and a part of western New South Wales (bottom right). This image was acquired by the European Envisat satellite’s Medium Resolution Imaging Spectrometer on 3 July 2010 at a resolution of 300 metre.

This Landsat satellite image shows a portion of Lake Eyre (lower-left corner) and the north-south sand dunes of the Simpson and Tirari deserts in the remote outback of South Australia. The Thematic Mapper on Landsat 5 acquired this image on 31 May 2011.

Earlier Australia from Space pictorials:

Australia from Space: Part 1

Australia from Space: Part 2

Australia from Space: Part 3

Australia from Space: Part 4

Adapted from information issued by ESA.

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Road to Mars – Six minutes of terror!

Jonathan Nally — Fri, 09 Dec 2011 09:00:46 +0000

Artist's impression of Mar Science Laboratory about to enter Mars' atmosphere.

THE MARS SCIENCE LABORATORY (MSL) team is calling it the “six minutes of terror”—the time between entering the Red Planet’s atmosphere and landing on its surface.

The NASA probe, carrying the Curiosity rover, will be using a totally new landing technique called the “sky crane”, whereby the six-wheeled vehicle will be lowered by cable down to the surface from an altitude of about 20 metres…courtesy of a rocket powered descent stage.

This graphic shows us the different parts of MSL: the cruise stage (which looks after the whole ensemble on the way to Mars); the backshell (which protects the rover during the cruise to Mars and initial atmosphere entry); the parachute (contained within the backshell); the descent stage (which will handle the final part of the descent); the rover itself; and the heatshield.

The Curiosity rover is kept safe by several layers of protection on the cruise to Mars, and during atmospheric entry and landing.

Doing most of the work during the atmospheric entry will be the huge heatshield. At 14 metres wide, it is the largest heatshield ever sent to another planet, and about half a metre wider than that used by the Apollo spacecraft in the 1960s and 1970s. It will need to withstand temperatures up to 2,100 degrees Celsius. These couple of photos will give you an idea of the size:

The space shuttle aside, Mars Science Laboratory's heatshield is the largest ever to be flown in space.

Here's another view, showing the craft upside down in a cradle.

Packed inside the backshell is the parachute, the largest ever sent to another planet. It’s also the largest “disc-cap-band” of any kind ever made. It is 16 metres wide and has 80 suspension lines that are 20 metres long. When deployed during the descent through Mars’ thin air, it will need to withstand a wind speed of Mach 2.2.

Here’s a photo of it, with some people standing nearby to give a sense of scale:

The huge parachute that Mars Science Laboratory will use to slow its descent through the Martian atmosphere.

And here’s a video of it being tested at AEDC’s National Full-Scale Aerodynamics Complex 40-metre wind tunnel—the largest in the world—at NASA’s Ames Research Laboratory in California. The action starts about 53 seconds in:

Quite impressive isn’t it? The parachute will deploy just over four minutes after atmospheric entry, and about two-and-a-half minutes before landing. At this stage the craft will be travelling at about 1,450 kilometres per hour! Twenty-four seconds after the parachute unfurls, with the speed down to about 500 kilometres per hour, the heatshield will drop away.

Another 70 seconds (approximately) and the parachute and backshell will detach, and the descent stage rockets will fire up for the final, powered descent stage.

The following video animation takes us through the interplanetary cruise phase, and the whole entry, descent and landing. Let’s keep our fingers crossed that everyone works as planned on August 6 next year!

Story by Jonathan Nally. Images and videos courtesy NASA.

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Australia from Space: Part 4

Jonathan Nally — Tue, 06 Dec 2011 13:01:01 +0000

MORE WONDERFUL IMAGES of Australia’s coastline, courtesy of the European Envisat Earth-monitoring satellite. Envisat was launched in March 2002 and at 8.5-tonnes is one of the largest satellites ever put into orbit. It circles the Earth every 101 minutes from north to south.

An Envisat MERIS image of the Great Barrier Reef centred on Cape York Peninsula. Taken on 19 August 2004, this MERIS Full Resolution mode images has a spatial resolution of 300 metres.

This Envisat image features the southern part of the Great Barrier Reef off Australia’s Queensland coast. It is the world’s most protected marine area, one of its natural wonders and a World Heritage site. Spanning more than 2,000 km and covering an area of some 350,000 sq km, it is the largest living structure on Earth and the only one visible from space. This image was acquired by Envisat’s Medium Resolution Imaging Spectrometer (MERIS) on 8 November 2010 at a resolution of 300 metres

Another view of the Great Barrier Reef. Australian researchers have discovered that Envisat's Medium Resolution Imaging Spectrometer (MERIS) sensor can detect coral bleaching down to 10 metres depth. This means Envisat could potentially map coral bleaching on a global scale. MERIS acquired this image on 18 May 2008, working in Full Resolution mode to yield a spatial resolution of 300 metres.

Sea and coral atolls off the West Australian coast, as seen by Envisat's MERIS ocean colour sensor.

Earlier Australia from Space pictorials:

Australia from Space: Part 1

Australia from Space: Part 2

Australia from Space: Part 3

Adapted from information issued by ESA.

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Earth from Space – Crepuscular rays

Jonathan Nally — Wed, 23 Nov 2011 13:01:19 +0000

Rays of light and dark appear to emanate from clouds in this image taken by an astronaut aboard the International Space Station. They are called crepuscular rays.

CREPUSCULAR RAYS OVER THE OCEAN near India are featured in this image photographed by an Expedition 29 crewmember on the International Space Station.

The sight of shafts of light, beaming down from the heavens through a layer of clouds, has provided many an artist, scientist, and philosopher with inspiration throughout the centuries.

Atmospheric scientists refer to this phenomenon as “crepuscular rays“, referring to the typical observation times of either sunrise or sunset.

Shadowed areas bounding the rays are formed by obstructions in the solar (or lunar) illumination pathway such as clouds or mountaintops; however this alone is not sufficient to create the phenomenon. The light must also be scattered—by airborne dust, aerosols, water droplets, or molecules of the air itself—to provide the visible contrast between the shadowed and illuminated parts of the sky.

A ground-based image of crepuscular rays shows them appear to radiate from a central point, a perspective effect. The orbital image above shows them in fact to be parallel.

When observed from the ground, crepuscular rays appear to radiate outwards from the source of illumination due to the effects of distance and perspective; however the rays are actually parallel.

This photograph from the Space Station provides an unusual viewing perspective from above the rays. The sun was setting to the west on the Indian subcontinent at the time the image was taken, and cumulonimbus cloud towers provide the shadowing obstructions.

The rays are being projected onto a layer of haze below the cloud towers. The image clearly illustrates the true parallel nature of the crepuscular rays.

See the full-size image here.

Orbital image courtesy NASA. Ground-based image of crepuscular rays from Wikipedia, courtesy Chevy111, posted under the Creative Commons Attribution-ShareAlike 3.0 License.

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