Wednesday, August 31, 2011

Mekong Delta, Vietnam

This Envisat image features Vietnam's Mekong Delta where the Mekong, the world's 12th longest river, fans out into tributaries and empties into the South China Sea in Southeast Asia.

Stretching from the glaciers of the Tibetan Qinghai Plateau to the South China Sea, the Mekong River flows some 4000 km through six nations China, Myanmar (Burma), Laos, Thailand, Cambodia and Vietnam.

In addition to 1500 species of fish, the river is home to the Mekong giant catfish, which can reach a length of three metres and weigh up to 300 kg. It also hosts the endangered Irrawaddy Mekong dolphin.

The 475 000 cubic km of water that the river discharges each year supplies the Mekong Delta's tropical wetlands with rich alluvial deposits. The wetlands act like sponges by storing and releasing water, making it ideal for rice cultivation.

In fact, such an enormous amount of rice is produced in the Mekong Delta that it is often referred to as Vietnam's 'rice bowl'. The rice grown there feeds the rest of the country and produces enough to make Vietnam the world's third biggest rice exporter, after Thailand and India.

Radar sensors, such as Envisats Advanced Synthetic Aperture Radar (ASAR), are particularly suited for monitoring rice cultivation because they are able to detect waterlogged ground and penetrate the humid cloud coverage typical of Asian rice-cultivating regions.

Ho Chi Minh (formerly known as Saigon), Vietnams largest city and chief port, is visible as white in the upper right corner.

The image was obtained by combining three ASAR acquisitions (9 January 2007, 13 February 2007 and 20 November 2007) taken over the same area. The colours in the image result from variations in the surface that occurred between acquisitions.

Istanbul, Turkey

The city of Istanbul, located astride the eastern edge of Europe and western edge of the Asian continent, shown in an Envisat radar multi-temporal composite image.

What is today Europe's third largest urban centre has been a major city for the last two thousand years. It has known three different names in that time: Byzantium when it was the gateway to Greek settlements on the Black Sea, Constantinople when it became the capital of the Eastern Roman Empire, then Istanbul when it fell to Muslim invaders in 1453.

In 1919 Istanbul lost its position as capital of Turkey, but remains that country's leading economic centre. Its population has grown from 2.84 million in 1970 to around ten million today, with settlers flocking from rural areas of Anatolia. Around 30% of all the cars owned in Turkey are in Istanbul.

Urban areas show up as white in this image the brightest areas being the most densely built-up. Among the densest is the old town, located on the west side of the city on the Emin�nu Peninsula, below the river estuary known as the Golden Horn. Further west along the coast are the runways of Ataturk International Airport.

Istanbul owes its prosperity to its status as a link between the Balkans, the Middle East and Central Asia, and to the high level of shipping that travels through the narrow Bosporus (Bosphorus) channel dividing Europe and Asia.

Some 48 000 ships pass through the Bosporus annually, three times denser than the Suez Canal traffic and four times as dense as the Panama Canal. Around 55 million tonnes of oil are shipped through here each year. Look closely along the Bosporus and bright points from individual ships can be seen. Also visible are the two bridges connecting the two continents, crossed by at least 45 000 vehicles daily.

Note the chain of islands known as the Princes' Islands (Kizil Islands) off the east side of Istanbul. The city faces onto the inland Sea of Marmara (Marmara Denizi), which has an area of around 11 350 square kilometres. The Bosporus links the Sea to the Black Sea. Note also Lake Iznik (Iznik Golu) towards the south-east corner of the image.

Because radar images measure surface texture rather than reflected light, there is no colour in a standard radar image.

Instead the colour in this image is due to it being a multitemporal composite, made up of three Advanced Synthetic Aperture Radar (ASAR) images acquired on different dates, with separate colours assigned to each acquisition to highlight differences between them: Red for 31 July 2003, Green for 17 April 2003 and blue for 26 February 2004.

The view was acquired in ASAR Image Mode Precision, with pixel sampling of 12.5 metres.

Tuesday, August 30, 2011

Canada's Maritime Provinces

This Envisat image highlights Canada's three Maritime Provinces New Brunswick, Nova Scotia and Prince Edward Island.

New Brunswick (the northern area of the large mass of land left of image centre) forms the land bridge linking this region to continental North America. It is bounded in the north by Qu bec and in the west by the US state of Maine (the southern area of the large land mass, visible).

With an area of approximately 73 440 sq km, New Brunswick is the largest of the provinces. New Brunswick differs from the other provinces because it is not wholly or nearly surround by water, making it sheltered from the Atlantic Ocean proper.

With an area of 55 284 sq km, Nova Scotia (the elongated body of land in bottom right) is Canada's second smallest province. The main peninsula is 550-km long and has 7500 km of coastline. Prince Edward Island (visible to the east of New Brunswick) is the smallest of the provinces.

The Gulf of St. Lawrence (visible above Prince Edward Island) is the outlet of North America's Great Lakes via the Saint Lawrence River into the Atlantic Ocean.

This image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument on 25 May 2008, working in Full Resolution mode to provide a spatial resolution of 300 metres.

The Caspian Sea

The shallow northern section of the Caspian Sea is shown in this Envisat image. Variously classed as an enormous lake or the smallest full-fledged sea, the Caspian is the largest landlocked water body in the world, with a surface area of 371 000 square kilometres.

The Caspian Sea is bordered by Russia, Azerbaijan, Iran, Turkmenistan and Kazakhstan. Stretching 1200 km from north to south, the almost-tide-free Caspian Sea fills a deep depression between Europe and Asia, its water level reaching around 28 metres below global ocean level. Its waters are not freshwater but salty although only about a third as much as true seawater. Its salinity is an inheritance from its origin as a remnant of the ancient Tethys Sea.

The northern part of the Caspian Sea is the most shallow, averaging about 10 metres deep, although its depth can shift by up to two metres, depending on variations in river flow and wind-driven currents. It appears bright blue here, probably due to a mixture of plant life and sediment stirred up by moving water.

This part of the Sea is also the location of vast oil and gas reserves, and the subject of major exploration and exploitation efforts, centred on the town of Atyrau at the mouth of the Ural River.

Around 130 rivers discharge into the Caspian, supplying around 300 cubic kilometres of freshwater annually. The two most significant rivers are both visible here. The Delta of the Volga River is visible in the left part of the image, while the Ural River can be seen flowing down from the image top centre. The Volga River is the longest in Europe, draining 20% of European land area and supplying 80% of the Caspian's freshwater inflow. The Ural River supplies 5% of its inflow.

The Sea's enclosed nature has enabled the preservation of some unique animals and plants. It also means that pollutants from industry and agriculture are concentrated within its brackish waters, threatening what are otherwise rich fisheries: the Caspian Sea is home to 85% of the world's stock of sturgeon and is the source of 90% of all black caviar. The Russian city of Astrakhan, located on the Volga Delta, remains at the centre of the caviar trade.

Along with increasing pollution, the Caspian Sea has also seen its water level fluctuate in past decades, at least partly due to human activity. As dams were constructed on rivers feeding the Sea its water level fell during the 1960s and 1970s, leading to construction on newly exposed shorelines. But since the late 1970s the water level began to rise again and has now risen by around 2.5 metres. Today it has stabilised and may even be falling again.

This image was acquired by the Medium Resolution Imaging Spectrometer (MERIS) instrument on Envisat on 22 September 2003, working in full resolution mode at 300 metre resolution.

Monday, August 29, 2011

Benelux and the English Channel

The green landscapes of Belgium, the Netherlands and Luxembourg, collectively known as Benelux, as seen by Envisat, along with a corner of France and the south-east coast of the United Kingdom across the English Channel (La Manche).

The collective term Benelux - from the first letters of each nation, originated from the Benelux Economic Union, which entered force in 1948 but has since been superseded by the European Union it helped inspire.

The three countries have a combined population of 27 million people, living in fertile, low-lying territory. Grey pixels seen on the image correspond to built-up areas; Benelux is the most densely populated region in Europe.

The most easterly country in the image is the Netherlands, located at the mouths of three major European rivers: the Rhine, the Meuse (Mass) and the Schelde, the latter just across from the Belgian border.

Clearly visible on the coast is the westerly section of the Waddenzee (Wadden Sea), a body of water and associated wetlands extending into Germany. Directly south of the Waddenzee are the IJsselmeer and Markermeer freshwater lakes. At the southern tip of the Markermeer is Amsterdam, with The Hague and Rotterdam further along the coast.

Just north of The Hague in the coastal town of Noordwijk is located ESA's European Space Technology Research Centre (ESTEC), where Envisat was designed, integrated and tested before being flown to French Guiana for launch in March 2002.

South of the Netherlands is Belgium, with the major cities of Antwerp and Brussels visible along with multiple settlements including Charleroi and Namur along the course of the Sambre River.

Directly east of southern Belgium is the small land-locked nation of Luxembourg, located within the darker greenery of the Ardennes, a region of dense forests and rolling hills.

Towards the western edge of the image we enter the Pas-de-Calais department in northern France, including the coastal cities of Calais and Dunkirk. Across the Channel is located the UK port of Dover. Sedimentary outflow from the River Thames is clearly seen - the same phenomena can be seen at smaller scales at the other river mouths in the image.

This 14 July 2003 image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) in Full Resolution mode. It has a spatial resolution of 300 metres and covers 672 x 672 kilometres.

Bloom in the Baltic Sea

A colourful summer marine plankton bloom fills much of the Baltic Sea in this Envisat image.

Plankton are microscopic marine plants that drift on or near the surface of the sea, by far the most abundant type of life found in the ocean. Just like plants on land they employ green-pigmented chlorophyll for photosynthesis - the process of turning sunlight into chemical energy.

While individually microscopic, plankton chlorophyll collectively tints the surrounding ocean waters, providing a means of detecting these tiny organisms from space with dedicated 'ocean colour' sensors.

As if dye had been placed in the water, the greenish colour highlights whirls of ocean currents. Floating freely in the water, plankton are sensitive not just to available sunlight but also to local environmental variations such as nutrient levels, temperature, currents and winds. Favourable conditions lead to concentrated 'blooms' like the one we see here.

Monitoring plankton is important because they form the base of the marine food web sometimes known as 'the grass of the sea'.

On a local level, out-of-control blooms can devastate marine life, de-oxygenating whole stretches of water, while some species of phytoplankton and marine algae are toxic to both fish and humans. It is useful that fishermen, fish farmers and public health officials know about such events as soon as possible.

Globally, plankton are a major influence on the amount of carbon in the atmosphere, and hence need to be modelled into calculations of future climate change.

Such blooms are common at this time of year in the Baltic Sea due to the combination of warm weather and waters rich in phosphorous nutrients. This phosphorous comes from the sea floor, having been released for surface layer plankton to consume when autumn and winter storms mix the water mass at the start of 2005 a severe storm caused mixing in a deep column of water.

The bloom seen here stretches around 200 kilometres from Lithuania, Latvia and the Russian territory of Kalingrad to the Swedish coast, surrounding the Swedish islands of Gotland and land. Blooms in the Baltic Sea are routinely monitored by the Finnish Environmental Institute (SYKE).

Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument is optimised for ocean colour detection, but also returns detailed multispectral information on land cover, clouds and atmospheric aerosols.

MERIS acquires continuous daytime observations in Reduced Resolution mode as part of its background mission. This is a detail from a MERIS Reduced Resolution image acquired on 13 July 2005, with a spatial resolution of 1200 metres.

Saturday, August 27, 2011

The Middle East

This Envisat image shows the blue eastern edge of the Mediterranean and the desert landscape of the Middle East.

The territory of numerous nations is covered, including Israel, Lebanon and Syria on the coast, Jordan to the east of Israel, and part of Saudi Arabia and Iraq.

Prominent at the bottom left of the image is the Dead Sea. Located at 417 metres below sea level, the Dead Sea is the lowest point on the Earth's surface. With a surface area of 1050 square kilometres, this water body is ten times more salty than the open sea. This salinity is too much for any fish to survive, although bacteria and fungi are found in its waters.

The Dead Sea is divided between Israel and Jordan. Note the greenish area just south of the Sea: this is a large complex of Jordanian salt evaporation ponds used to produce sodium chloride and other salts for the chemical industry and human and animal consumption.

On either side of the northern edge of the Dead Sea can be seen grey areas indicating built-up areas: with Amman, the capital of Jordan, to its east and Jerusalem to its west. The town of Bethlehem is positioned south of Jerusalem, within the West Bank.

The water body north of the Dead Sea - connected to it by the Jordan River as it follows the course of the Great Rift Valley - is the Sea of Galilee, also known as Lake Tiberias. The settlement of Nazareth lies to its west.

At the top right of the image can be seen the green and fertile banks of the Euphrates River, running through Syria towards the Iraq border.

This 11 June 2003 image was acquired by the Medium Resolution Imaging Spectrometer (MERIS) on Envisat, operating in full resolution mode, with a resolution of 300 metres.

Friday, August 26, 2011

Lake Volta, Ghana, Africa

This is one of the largest artificial bodies of water in the world, as seen by ESA's Envisat from 800 kilometres away in space.

Lake Volta dominates the territory of the West African state of Ghana. Formed by the construction of the Akosombo Dam over the River Volta in the mid-1960s, it has an area of 8 482 sq km. Lake Volta is used to generate electricity and provide inland transportation, and its waters are also used for irrigation and fishing.

The image clearly illustrates the divide between the verdantly forested ''Ashanti' region in the southeast of the country and the sparser lowland savannah and plains to the north.

Towards the top of the plateau can be seen road networks leading to and from the settlement of Kumasi, Ghana's second city with a population of two thirds of a million. Southeast of Kumasi is the circular Lake Bosumtwi, a flooded meteorite crater - in fact one of only 18 confirmed African impact craters.

On the coast of the Gulf of Guinea, south of Lake Volta, is located the sprawling capital Accra, Ghana's largest city with approximately 1.6 million inhabitants.

This 12 February 2003 image was acquired by the Medium Resolution Imaging Spectrometer (MERIS) instrument on Envisat, working in Full Resolution mode. The image has a resolution of 300 metres and covers 450 km by 670 km.

Brazil's Amazon Basin, South America

The eastern part of Brazil's Amazon Basin and rainforests, located in the state of Par , is highlighted in this Envisat image.

The Amazon Basin is drained by the Amazon River, located to the east (not visible), and its tributaries. The brownish sediment-laden water visible flowing at the top of the image is the Par� River, the southern arm of the mouth of the Amazon.

Belem (barely visible to the right of the Par� in the upper left), the state capital of Par�, is located on the Par� Rivers south bank.

Dark river waters visible flowing just under the Par� belong to the Tocantins River, which runs roughly 2500 km from south to north. The large dark area visible in the image centre is the reservoir that was formed by the Tucurui dam on the Tocantins River, flooding some 2430 km� of forestland.

This image clearly highlights the contrast between the rainforest (dark green areas) and sprawling land cultivation (the fishbone-like patterns). Light green colours indicate agricultural areas which where covered by rainforest before.

Rainforests worldwide are being destroyed at an alarming rate, a development of great concern because of the role they play in global climate and because they are home to nearly half of the worlds species of plants, animals and insects. Unlike other forests, rainforests do not grow back when they are destroyed and their soils are not suitable for long-term agricultural use.

All countries in the Amazon region are now looking into ways of exploiting its natural resources in a sustainable manner without destroying the rainforest any further. Environmentalists and Indians are working together to create markets for products such as nuts, fruits, oils and pigments.

With their unique view from space, Earth observation satellites have been instrumental in highlighting the vulnerability of the rainforests by documenting the scale of deforestation, particularly in remote areas.

This image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) on 23 June 2008, working in Full Resolution Mode providing a spatial resolution of 300 m.

Thursday, August 25, 2011

Lake Mead, Nevada-Arizona, USA

This Envisat image features the manmade Lake Mead, located east of Las Vegas (visible) and west of the Grand Canyon along the border of the US states of Arizona (bottom, east of river) and Nevada (the rest).

The 20th century was the great age of dam building, which did more to change the face of our planet than any other single human activity. Lake Mead was established in the early 1930s by the construction of the Hoover Dam on the Colorado River (bottom).

The Hoover Dam (green area between the lake and river) was one of the first of some 45 000 major dams to be constructed on rivers worldwide. It controls the flow of the Colorado, irrigates farmlands and supplies hydroelectric power and dependable water to people in the southwestern US and northern Mexico.

Its reservoir, Lake Mead, is one of the largest in the world, with a surface area of 593 sq km. However, an 11-year drought and increased water consumption due to population growth have resulted in a decline in its water levels. This month, it fell to its lowest point (330 m above sea level) since it was filled 75 years ago.

With some 90% of southern Nevadas water coming from the lake, authorities are watching its levels closely. If the water level dips to 327 m, a shortage will be declared and a set of rationing measures will be implemented.

This image was created by combining three Envisat radar acquisitions (15 May, 19 June and 24 July 2010) over the same area. The colours result from changes in the surface that occurred between acquisitions.

Wednesday, August 24, 2011

Salty plain, Bolivia, South America

This Envisat image features salt flats in the Department of Potosi in southwest Bolivia, near the crest of the Andes Mountains.

The Salar de Uyuni (the lower white area) is the largest salt flat in the world, occupying 10 582 sq km. It is located at the southern end of the Altiplano, a high plain of inland drainage in the central Andes.

Some 40 000 years ago, this area was part of a giant prehistoric lake that dried out, leaving behind two salt flats, the Uyuni and the Salar de Coipasa (visible above Uyuni), as well as two modern lakes, Poop (visible in green) and Uru Uru.

Occupying 2218 sq km, Salar de Coipasa is Bolivia's second largest salt flat.

Stretching 90 km in length and 32 km in width, Lake Poop� is the country's second largest lake with the permanent part of its body covering approximately 1000 sq km.

This image was acquired by Envisats Medium Resolution Imaging Spectrometer (MERIS) instrument on 7 May 2008 working in Full Resolution mode to provide a spatial resolution of 300 m.

Lake Tana, Ethiopia, source of the Blue Nile

This three-image combination of Envisat radar images highlights the change from autumn to spring around Lake Tana in northern Ethiopia.

With a surface area of 2156 square kilometres but an average depth of only 14 metres due to high levels of sediment. Lake Tana is the largest single lake in Ethiopia and forms the main reservoir for the Blue Nile. The Lake is located at an altitude of 1788 metres on the north central plateau of Amhara.

Lake Tana is used for fishing, farming and transportation, and has a thriving tourist industry centred on the more than 30 islands on the Lake, home to numerous Ethiopian Orthodox Church monasteries dating back more than five centuries.

The Blue Nile runs from Lake Tana's southeast corner, flowing south over a lava dam to form the Tisisat Falls - the name in Ethiopian means 'the water that smokes' - then flowing northwest to merge with the White Nile and form the full-fledged Nile itself. The Blue Nile contributes two thirds of all the Nile discharge, along with most of the sediment carried along 4750 kilometres through to Egypt and the Mediterranean.

To the northeast of the lake is Simen Mountains National Park, a UNESCO World Heritage Site. These jagged mountain peaks and deep gorges are home to a number of rare animals including the Gelada baboon and Walia ibex, a type of goat.

Radar images measure surface roughness rather than reflected light, so the smooth Lake waters are as distinctive as the harsh landscape around it. The colour in the image comes from the fact that this is actually a combination of three Envisat Advanced Synthetic Aperture Radar (ASAR) images, and is used to highlight changes occurring between acquisitions.

A colour is assigned to each date of acquisition: red for 3 September 2003, green for 27 November 2003 and blue for 4 March 2004. The images were acquired in wide swath mode, covering an overall span of 400 km.

Tuesday, August 23, 2011

Vancouver and Seattle, Pacific Northwest

Vancouver and Seattle, the two major port cities of the American Pacific Northwest, nestle in sheltered sea channels flanked by snow-covered mountains in this Envisat image.

Vancouver is the largest port in Canada, with an overall metropolitan area population of two and a half million. It is located towards the centre of the image, on the Strait of Georgia, a body of water shielded from the Pacific by the bottom end of Vancouver Island. Look closely to see a greenish-black grid pattern covering the flat terrain.

Around Vancouver the Coast Mountains to the north turn into the Cascade Mountains when south of the United States border, just below the city of Vancouver itself. On the other side of the mountains the flat, dry wheat prairies begin.

The United States port of Seattle is to be found some way below Vancouver towards the southern end of the sheltered channel, between the east side of Puget Sound and Lake Washington. It is a major economic centre, with an overall metropolitan area of about 3.7 million people.

Facing Seattle to the west is the snowy, forested Olympic Peninsula, topped by Mount Olympus. To its south is found Mount Rainier, a dormant volcano clad with glaciers, and the tallest peak of the Pacific Northwest.

This 15 February 2005 Medium Resolution Imaging Spectrometer (MERIS) image was acquired in Full Resolution Mode, providing a spatial resolution of 300 metres and covering a width of 672 kilometres.

Dongting Lake and the Yangtze River, China

China's longest river and its second largest lake are central features of this Envisat Advanced Synthetic Aperture Radar (ASAR) image.

Dongting Lake is the large L-shaped body of water, seen towards bottom right in the image. It - and the Central Yangtze region in general - is an important habitat for numerous aquatic species including the Yangtze freshwater dolphin. Dongting's total area varies considerably as Yangtze flood waters pour into the lake between July and September, the period within which this image was acquired.

Dongting's official area is 2740 square kilometres, less than half the 6200 square km size it was measured at a century and a half previously its size having been reduced by rapid sedimentation and reclamation for farmland.

In winter this shrinkage means the lake is more or less split into three separate basins, West, South and East Dongting, but each summer the three water bodies become a single lake of about 3900 square km or more.

Several rivers join onto Dongting Lake, the most famous being the Yangtze, winding down from towards top left before carrying on out of the right side of the image. Note the several oxbow lakes formed on its right bank. The Yangtze is the longest river in Asia and the third longest in the world, snaking for 6300 km across China and serving as a drain for 1.8 million square km of territory.

Also feeding into Dongting Lake are rivers including the Yuan, coming from the left, Yiang, from the bottom, and Zi, lying between them.

The heart-shaped water body above the Yangtze to the right side of the image is Lake Hong, known across the country for its beauty and significant as a site for fishing and crab breeding.

This image is a 240-km wide section from an ASAR Wide Swath image acquired 16 August 2003.

Monday, August 22, 2011

Gulf Of Oman, dust storm

This image is dominated by a dust and sand storm covering up the Gulf of Oman.

The scene shows a large part of Baluchistan, a mountainous region, with some deserts and barren plains, covering southwestern Pakistan and southeastern Iran (top right top center).

More towards the east, the Indus river providing irrigation to the valley plains, and throwing itself into the Arabian Sea about 100km southwest of Karachi, Pakistans largest city and chief port. The top right area of the image shows a part of the Thar Desert also known as the Great Indian Desert.

The Thar Desert is located in east Pakistan and northwest India and is bounded by a salt marsh called Rann of Kutch on the south. Soutwest of the image is the Arabian Peninsula completely covered under a veil of dust and sand, just as the Gulf of Oman, the principal vain for oil tankers from the nations around the Persian Gulf.

The dust and sand are transported for over 450 km off the coast. This kind of storm is a regular phenomenon in the area, which is usually due to very strong Shaman winds. The storms do not only interrupt daily life, they cause havoc, and present a danger for health and food security.

The frequency of the storms may be influenced by human activity, through heavy drainages in arid environments.

This Envisat Medium Resolution Imaging Spectrometer (MERIS) image was aquired on 13 December 2003 working in full resolution mode to provide a spatial resolution of 300 metres.

Iceland, a land of fire and ice

This Envisat image features a snow-covered Iceland, a volcanic island famous for its volcanoes, glaciers, lakes, lava and hot springs.

Located in the North Atlantic Ocean east of Greenland and immediately south of the Arctic Circle, Iceland is the westernmost European nation, and has more land covered by glaciers than the whole of continental Europe.

Visible in the lower left of the image is Lake Pingvallavatn, the largest lake in the country. It was on the banks of this lake that one of the worlds first republican governments was established in 930.

Also visible is the countrys capital, Reykjavik, located on the western coast, slightly southwest of Lake Pingvallavatn. With a population of more than 100 000, it is a major port and the country's largest commercial centre.

Glaciers cover over 11 percent of Icelands landscape, the largest being the Vatnajokull glacier (located in the southeast), which at 8000 square kilometres is also the largest in Europe. Volcanoes also dominate the landscape with more than 100, of which a large number are still active, rising on the island.

There are also some 800 hot springs present with an average water temperature of 75 degrees Celsius. Reykjavik, Icelandic for Smoky Bay, was named for steam rising from hot springs in a southwestern bay. Geothermal water reserves provide Icelands population with most of its electricity and heating.

Swirls of blue and green seen off the south and western coasts are caused by concentrations of plankton. These small organisms form the basis of the ocean's food chain and have an essential role in the global ecosystem.

Although individually minute, the total biomass of plankton is probably greater than that of all marine animals put together. Plankton forms the basis of the marine food web, and its presence offshore helps account for Iceland's rich fisheries.

This Envisat Medium Resolution Imaging Spectrometer (MERIS) image was aquired 0n 26 February 2007 working in full resolution mode to provide a spatial resolution of 300 metres.

Saturday, August 20, 2011

The Niger delta, Nigeria

This Envisat image highlights the lower Niger River system in the West African country of Nigeria, where the Niger River (left) and the Benue River merge.

With a length of 4180 km, the Niger River the longest and largest river in West Africa is the third longest river in Africa, after the Nile and Congo. It originates in the highlands of southern Guinea and flows through Guinea, Mali, Niger, Benin and Nigeria.

The Benue River, Nigers longest tributary with a length of about 1400 km, joins the Niger at the town of Lokoja. From this confluence, the Niger makes a nearly 90-degree turn southward and flows in that direction until it empties in the Gulf of Guinea in the Atlantic Ocean.

Before entering the gulf, the Niger forms a wide, fan-shaped delta that spans nearly 190 km and makes up more than seven percent of Nigerias land mass. The delta holds some of the worlds richest oil deposits.

Lagos city, the former capital of Nigeria, is located to the west of Lagos Lagoon (visible as a dark blue, bird-shaped body of water along the coast to the left of the Niger).

Also visible are the Kainji (the bright green body of water with tan sediment in the upper right hand corner) and Shiroro (the light green body of water above and to the left of where the Niger and Benue meet) Reservoirs.

This image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument on 12 December 2007, working in Full Resolution mode to provide a spatial resolution of 300 metres.

Blooms in the North Atlantic Ocean

Resembling the brush strokes of French Impressionist Claude Monet, electric blue-coloured plankton blooms swirl in the North Atlantic Ocean off Ireland in this Envisat image.
Plankton, the most abundant type of life found in the ocean, are microscopic marine plants that drift on or near the surface of the sea.

Plankton have been called 'the grass of the sea' because they are the basic food on which all other marine life depends. Since plankton contain photosynthetic chlorophyll pigments, these simple organisms also play a similar role to terrestrial 'green' plants in the photosynthetic process.

Plankton are able to convert inorganic compounds such as water, nitrogen and carbon into complex organic materials. With their ability to 'digest' these compounds, they are credited with removing as much carbon dioxide from the atmosphere as vegetation on land.

While individually microscopic, the chlorophyll they use for photosynthesis collectively tints the surrounding ocean waters, providing a means of detecting these tiny organisms from space with dedicated 'ocean colour' sensors, like Envisat's Medium Resolution Imaging Spectrometer (MERIS).

The island of Ireland comprises the Republic of Ireland (covering five-sixths of the island to the south) and Northern Ireland (top eastern corner). The islands brown rugged cliffs along the west coast stand in contrast to the green lush lowlands of its interior.

Ireland has some 14 000 km of inland waterways along with some 800 lakes. The large dark blue lake seen in Northern Ireland is Lough Neagh, the islands largest lake with an area of 392 sq km. Located some 30 km east of the lake is Northern Irelands capital city of Belfast. Dublin, the capital of the Republic of Ireland, is located on the east coast (covered by clouds).

The Irish Sea, a portion of Scotland (top) and the Isles of Man (top right) are visible to the east of Ireland.

Friday, August 19, 2011

Qeshm Island, Iran

This Envisat image features the largest island in the Persian Gulf: Irans Qeshm Island.

This long thin island lies just a few kilometres off the Iranian coast near the narrow Strait of Hormuz, which separates the Persian Gulf to the west and the Gulf of Oman to the southeast.

At its narrowest, the Hormuz Strait is just 54 km wide. However, this strait is one of the most strategically important passageways in the world because it is the only route to the open ocean for much of the Persian Gulf. Around 17 million barrels of crude oil are shipped through this passage every day.

Despite lying in this busy shipping lane, Qeshm Island harbours the Hara Biosphere Reserve, the largest stretch of mangrove forest along the Persian Gulf shoreline.

This network of shallow waterways and forest can be seen clearly in the image, between Qeshm Island and the mainland. The lush marine forest attracts many species of migrating birds, turtles, sea snakes, insects, frogs and mammals.

Qeshm Island is about 14 km long and 11 km wide, ringed by coral reefs. Inland, low-lying mountains made up of sedimentary layers cover much of the surface.

The image was created by combining three Envisat radar images from 2009 (7 May, 29 October and 3 December) over the same area. The colours result from changes in the surface between acquisitions.

Europes largest port, Rotterdam, The Netherlands

The port of Rotterdam and the province of Zeeland, both located in the southwest of the Netherlands, are highlighted in this Envisat image.

Rotterdam port (visible on left a quarter of the way down from top) is the largest port in Europe and the gateway to some 450 million consumers. The port, located on the North Sea, area stretches over 40 km in length and covers 10 000 hectares. It has a depth of 24 m.

Rotterdam, the countrys second largest city after Amsterdam, is located on the New Meuse River, formed by the Rhine and Meuse rivers, that divides the municipality into its northern and southern parts. The city centre is situated on the northern bank (visible in light green).

The large body of water in the middle of the image beneath Rotterdam is Haringvliet. Haringvliet dam, which took 14 years to complete, is visible as a brownish bridge closing the mouth of the river off from the North Sea. Its 17 openings allow it to regulate the amount of water flowing to the sea.

The dam was constructed as part of the Delta Plan a number of dams, sluices, locks, dikes and storm surge barriers built between 1950 and 1997 in the southwest of the Netherlands to reduce the length of and reinforce the coastline.

In 1953, a tidal wave broke the existing dikes and flooded the area, killing nearly 2000 people and 50 000 heads of cattle. The Delta Plan was inaugurated twenty days after the flood. Volkerak dam, also part of the plan, is visible in the image at the eastern end of Haringvliet.

The third body of land (lower left hand corner) is part of the province of Zeeland, a large river delta that mostly lies below sea level.

This image was acquired by Envisats Advanced Synthetic Aperture Radar (ASAR) instrument in Image mode with a resolution of 12.5 m.

Thursday, August 18, 2011

Poyang Hu, China

This Envisat image shows the patchy waters of Poyang Lake (Poyang Hu) in winter. In summer it is the largest freshwater body in China but in the dry season Poyang Lake shrinks back to less than a third of its former size.

Poyang Lake is situated in Jiangxi Province, around 50 kilometres north of the city of Nanchang (outside the image). The Lake's basin is one of the People's Republic of China's most important rice-producing regions, but local inhabitants must contend with massive seasonal changes in water level, topped by regular severe floods.

Poyang Lake is connected to the Yangtze (Chiang Jiang) River through a narrow channel, exiting at the top left corner of the image. By the end of the rainy season the Lake can extend up to 3500 square km in area, but during the dry season it may shrink to under 1000 square km.

The receding waters leave behind a system of wetlands and mudflats which attract up to half a million migratory waterfowl, including such rare species as Siberian and White-naped Cranes.

Improved understanding of Poyang Lake's annual dynamic promises to aid flood mitigation, and as part of ESA's Dragon Programme of cooperation with China, Envisat's Advanced Synthetic Aperture Radar (ASAR) monitored Poyang Lake's hydrological cycle in detail during 2004 and 2005.

ASAR is sensitive to water or waterlogged surfaces, which show up as dark because radar signals bounce away off flat water surfaces. Built-up areas appear brighter because they reflect radar signals straight back towards the sensor antenna.

Examples here include the city of Duchang, located towards top left (note also an apparent bridge across the water to its southwest, with more bridges visible in red elsewhere), the town of Poyang just right of the image centre, and Yugan towards the image base.

This image was acquired on 29 December 2005 by Envisat's ASAR operating in Alternating Polarisation (AP) mode, performing a simultaneous acquisition of data in two radar polarisations to gather added detail. The image has a pixel sampling of 75 m and a width of 82.3 km.

Florida's 'River of Grass' USA

This Envisat image features the southern tip of Florida, located in the southeast region of the United States. The peninsula juts outs into the Atlantic Ocean (right) and the Gulf of Mexico for more than 550 km.

The brown circular area is Lake Okeechobee, the third largest freshwater lake contained entirely within the country (after Lake Michigan and Iliamna Lake). It covers an area of about 1900 sq km, has a shoreline of 220 km and an average water depth of 4 m.

The United States largest subtropical wilderness, the Everglades, covers some 10 000 sq km on the tip of the peninsula. This area features shallow, slow-moving water and is abundant in a plant called sawgrass that becomes so thick it makes the water barely visible, earning the Everglades the nickname River of Grass.

Home to diverse animal and plant life, the Everglades is the worlds only place where crocodiles and alligators exist alongside each other. Its wetlands also serve to mitigate storm systems and provide south Florida residents with drinking water.

The Everglades have been designated a Wetland of International Importance by the Ramsar Convention on Wetlands, a World Heritage Site and an International Biosphere Reserve by the UN.

Located southeast of the Lake Okeechobee is the Arthur R. Marshall Loxahatchee National Wildlife Refuge (dark brown, tear-drop shape). The refuge provides habitat for the wildlife of the northern Everglades.

Miami is visible in pale green just beneath the National Wildlife Refuge on the coast, while the city of Orlando can be seen in pale green just inland from the Atlantic Ocean coastline above Lake Okeechobee.

The various colours of green visible in the Gulf of Mexico are due to sediments being transported in the water. The shallow blue waters of the Bahamas can be seen in the bottom right between clouds.

The islands visible extending southwest from the southern tip of the peninsula are the Florida Keys.

This image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument on 5 February 2009, working in Full Resolution mode to provide a spatial resolution of 300 m.

Wednesday, August 17, 2011

Yucatan Peninsula, Mexico, Central America

The northern tip of Mexicos Yucatan Peninsula, a northeastern projection of Central America, is visible in this Envisat image. Merida, the Yucatan state capital, is clearly seen as a large whitish area to the west some 35 km from the Gulf of Mexico.

The Yucatan Peninsula was once home to the Mayan civilisation, and Merida known as the White City because of its large use of white limestone and paint was built over an ancient Mayan city.

Mayan ruins along with picturesque beaches and verdant forests bring many tourists to the peninsula, which is famous as the site of the asteroid impact that killed the dinosaurs.

The peninsula is located between the Gulf of Mexico to the west and north and the Caribbean Sea (not visible) to the east. In addition to the Mexican state of Yucatan, the peninsula also includes the states of Campeche, Quintana Roo and large portions of Belize and Guatemala.

Visible in the Gulf of Mexico is Alacranes reef, an emergent platform reef that forms part of the Campeche Bank, an underwater extension of the Yucatan Peninsula. Alacranes is the largest reef in the southern Gulf of Mexico and the only coral reef in Yucatan.

The Alacranes reef has great biological diversity and was declared a national reserve in 1994. The protected area of some 88 084 hectares includes five islets Desterrada, Desertora, Perez, Chica and Pajaros.

This image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) on 26 February 2007 working in Full Resolution mode to provide a spatial resolution of 300 metres.

Patagonia Plateau, South America

This Envisat image highlights the contrasting landscapes of the Patagonia Plateau in Argentina (right) and southern Chile (left) with lush greenery, white glaciers, aquamarine lakes and brown arid steppes visible.

The Andes Mountains (stretching down the centre of the image) form a natural boundary between the two South American countries and are responsible for the high contrast in landscape.

Argentinas Los Glaciares National Park, named a UNESCO (United Nations Educational, Scientific and Cultural Organisation) World Heritage site in 1981, is situated in the area around the two large glacial lakes just beneath the centre of the image. The park is named after the glaciers located in the Southern Patagonian Ice Field the largest ice mass in the Southern Hemisphere.

The majority of the nearly 50 big glaciers fed by the Patagonian Ice Field in the park have been retreating during the last 50 years. The 30-km-long Perito Moreno glacier, the most famous glacier in the park because of its rupture process, is one of the few not retreating or advancing but rather in equilibrium, going through cycles of retreats and advances.

Located on a narrow channel that separates the main body of Lake Argentino (the large lake seen near the bottom of the image above) from its southern arm (Brazo Rico), Perito Moreno forms an ice dam when it advances to the extent that it reaches the land on the other side of the channel, creating two separate bodies of water.

Once the dam is formed, water and ice commence a kind of duel: water from melting glaciers drain into the trapped section of lake, and the force of the rising waters inevitably becomes too much and the ice dam gives way to crushing lake waters trapped behind it, finally breaking apart. This process first occurred in 1917, submerging a several-hundred-year old forest, and has occurred some twenty times since then.

The three large turquoise lakes visible on the Eastern side of the ice field in the satellite image (from top to bottom) are Lake OHiggins, Lake Viedma and Lake Argentino the biggest lake in Argentina with a surface area of nearly 1500 square kilometres. Their unique colour is attributed to glacier milk, suspended fine sediment produced by the abrasion of glaciers rubbing against rock.

This image was acquired on 15 March 2007 by Envisats Medium Resolution Imaging Spectrometer (MERIS) instrument while working in Full Resolution mode.

Tuesday, August 16, 2011

Foxe Basin, North East Canada

This is a nighttime thermal image showing pack ice over the Foxe Basin in North-east Canada. Acquired by Envisat's Advanced Along Track Scanning Radiometer (AATSR) this image is oriented northeast to southwest and centred over the latitudinal boundary of the Arctic Circle.

AATSR is equipped with thermal infrared channels to measure land and sea surface temperatures, accurate to a fraction of a degree. The ice covering the Foxe Basin is whitish-blue in colour while the snow-covered land appears deep blue or black in colour.

Located north of Hudson Bay between the Melville Peninsula and the large Baffin Island, Foxe Basin is a broad depression whose depth varies between 100 and 400 metres. The island with the Basin at the top of the image is Prince Charles Island, with Southampton Island at image bottom.

The Basin remains ice-covered for most of the year, with landfast ice dominating in the north and pack ice covering the deeper southern waters. Foxe Basin is rarely ice free until September, with open pack ice common throughout the summer.

It is named after Luke Foxe, who explored this area widely in the seventeenth century in the vain hope of finding a Northwest Passage across North America.

It may appear forbidding, but this is one of the most biologically rich and diverse areas of the Canadian Arctic. The many polynyas of northern Foxe Basin supporting colonies of bearded seals and the largest walrus herd in Canada. Ringed seals are polar bears are common, and it is also a summering area for bowhead, beluga and narwhal whales.

This AATSR image was acquired on 28 January 2004, during Envisat's ten thousandth orbit of the Earth, and has a one-kilometre resolution.

Gobi Desert, Mongolia

This Envisat radar image features the terrain of the Gobi Desert, which stretches across vast areas of the Mongolian People's Republic and the Inner Mongolian Autonomous Region of China.

The Gobi, which is about 1600 km in extent from east to west and about 1000 km from north to south, has a total area of 1 300 000 sq km, making it the largest desert in Asia and the fourth largest in the world.

Despite the connotations associated with deserts being sandy, the Gobi Desert is covered with bare rock. It is formed by a series of small basins within a larger basin rimmed by upland. The basin floors are unusually flat and level, and are formed of a desert pavement of small gravel atop granite or metamorphic rock.

The Gobi, which is Mongolian for 'waterless place', receives no more than 200 to 250 mm of rain along the northern and eastern edges, but only its southeastern portion is completely waterless.

Numerous small lakes that are kept filled by groundwater are visible in the image. Archaeological evidence shows the lakes have existed for a very long time, with Stone Age dwellers living along their borders. Many important fossils have been found in the Gobi Desert, including the first dinosaur eggs.

Envisats Advanced Synthetic Aperture Radar acquired this image on 6 August 2009.

Monday, August 15, 2011

The Last Frontier, Alaska

This Envisat image features the southern part of Alaska, which is located in the extreme northwest of the North American continent.

Covering more than 1 500 000 sq km, Alaska is the largest US state by area. Its rugged landscape and climate coupled with the fact that it is the least densely populated state has earned it the nickname The last Frontier.

Snow-covered mountain ranges dominate the image. The crescent-shaped Alaska Range (visible in the upper left corner) is home to Denali (also known as Mount McKinley), the highest peak in North America (over 6000 m above sea level).

The Chugach Mountains, which contain the states greatest concentration of glacial ice, are visible extending eastward along the southern coast for some 500 km. When warm, wet air flows off the Pacific Ocean (visible bottom right) and meets the cool temperatures of this mountain range, some of the highest snowfall in Alaska is created.

The Kenai Mountains cover the southern and eastern portions of the Kenai Peninsula (left of image centre), which is separated from the mainland by the Cook Inlet (a bay of the Pacific Ocean that is visible west of the peninsula in shades of blue, green and tan).

Several rivers and lakes dot the peninsula. Lakes Tustumena (large light blue lake to the south), Skilak (above Tustumena) and Kenai (L-shaped lake northeast of Skilak) are clearly visible.

Kodiak Island (visible in bottom left) is Alaskas largest island and the USs second largest, behind the Big Island of Hawaii. Kodiak bears, the worlds largest living carnivores, are found only on Kodiak and neighbouring islands. They can grow more than 3 m long and weigh more than 780 kg.

Anchorage (visible in light green), the states largest city, is situated at the head of Cook Inlet. The annual dogsled race known as the Iditarod Trail Sled Dog Race begins in Anchorage.

Sediments being transported in the water along the southern coast and Cook Inlet have coloured the waters shades of green, blue, tan and gray.

This image was acquired by Envisat\'s Medium Resolution Imaging Spectrometer (MERIS) instrument on 18 May 2009.

Lakes of Central Asia

This Envisat image highlights several of the lakes in the southeastern part of the Republic of Kazakhstan and in the northeastern area of Kyrgyzstan.

With a territory of some 2 727 300 sq km, Kazakhstan is the ninth largest country in the world. Situated in the centre of the Eurasian continent, it borders Russia to the east, north and northwest, the Caspian Sea to the west, the People's Republic of China to the southeast and Kyrgyzstan, Turkmenistan and Uzbekistan to the south.

The eastern end of Lake Balkhash, the second largest lake in Central Asia, is visible in the upper left hand corner. Lake Balkhash, which contains freshwater in the west and saltwater in the east, covers an area over 16 000 sq km and has a length of some 600 km. A sandbank at the Saryisek peninsula the Lake's narrowest part - divides the two halves.

The Ili, Karatal and Aqsu Rivers feed the lake, which is located 966 km east of the Aral Sea. Like the Aral Sea, Lake Balkhash is shrinking due to river waters being diverted that would otherwise go to replenish it. The Ili River was dammed in 1970 to form the Kapchagayskoye Reservoir (second large body of water visible one third of the way up from bottom).

Lakes Sasykkol (the most northerly lake visible), a freshwater lake, and Alakol, a saltwater lake, are located some 180 km east of Lake Balkhash. Lake Alakol (below Sasykkol) has an area of 2655 sq km and reaches a depth of about 45 m. The smaller body of water located between them is the brackish Lake Koshkarkol.

Sayram Lake, located within China's Xinjiang province, is visible south of Lake Alakol. The sapphire-coloured lake is the largest and highest alpine lake in Xinjiang and is surrounded by the Borohoro Shan mountain range.

The dark lake at the bottom left of the image is Lake Issky-Kol. Its dark colour is due to its 668-metre depth. Lake Issky-Kol has an area of 6200 sq km, making it one of the largest mountain lakes in the world. Despite being surrounded by snowy peaks, its slightly saline water does not freeze in winter.

The snow-capped Tien Shan mountain range is visible just beneath Lake Issky-Kol. The mountain range, which stretches some 2400 km, forms part of the boundary between Kyrgyzstan, southeastern Kazakhstan and China.

Also visible in the image is the former Kazakhstan capital of Almaty, located at the foot of the snowy mountains, north of the middle of Lake Issky-Kol. Since 1998 Astana, closer to the centre of Kazakhstan, has served as the capital.

This image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument on 12 September 2007, working in Full Resolution mode to provide a spatial resolution of 300 metres.

Saturday, August 13, 2011

Volga Delta, Europe

This Envisat image features the Volga Delta, which forms where the Volga River empties into the northwestern part of the Caspian Sea, the largest inland body of water in the world.

The Volga River is the longest in Europe, draining 20% of European land area and supplying 80% of the Caspian's freshwater inflow. When water from the river enters the Volga Delta, Europes largest inland river delta, it splits up into more than 1000 waterways.

The delta is considered one of the world's most dynamic river deltas because of its remarkably complicated hydrographic network. It has been designated as a Wetland of International Importance by the Ramsar Convention on Wetlands because it provides habitat for many migratory birds. It has also been nominated for inscription on the UNESCO World Heritage List.

The Caspian Sea contains more than 78 000 cubic km of waterabout one-third of Earths inland surface water. Stretching 1200 km from north to south, the elongated, almost tide-free sea fills a deep depression (some 27 m below sea level) between Europe and Asia.

The sea is bordered by Russia and Kazakhstan to the north, Azerbaijan to the west, Turkmenistan to the east and Iran to the south. Covering an area more than 380 000 sq km, it is larger than Japan.

Since the sea has no outlet, many unique animals and plants have been preserved. For instance, it is home to 85% of the world's stock of sturgeon and is the source of 90% of all black caviar. The Russian city of Astrakhan, located on the Volga Delta about 100 km from the sea (visible in yellow just above the triangular-shaped delta), remains at the centre of the caviar trade.

The sea's water levels have fluctuated in the last few decades, a development at least partly due to human activity including the building of dams. The northern part of the Caspian (shown here) is the shallow end, averaging around 6 m. The southern part is the deepest, reaching over 1000 m.

Bright yellow dots visible outside the delta area near Astrakhan indicate sand dunes. This area, used for raising cattle and sheep, is also characterised by saline soils and sparse sage vegetation.

This image was acquired by Envisats Medium Resolution Imaging Spectrometer (MERIS) instrument on 2 June 2009.

The French Frigate Shoals, Pacific Ocean

The French Frigate Shoals, highlighted in this Proba image, is an atoll consisting of a 35-kilometre crescent-shaped reef surrounding a dozen small islets located in the Pacific Ocean about 800 kilometres northwest of Honolulu, Hawaii.

The French Frigate Shoals’ coral reefs grow atop an eroded volcano that has been submerged for millions of years. The only remnant left of the volcano today is a unique 36-metre-high rock formation, named La Pérouse Pinnacle, which protrudes out of the water in the centre of the atoll (seen right of the centre).

The name of the pinnacle, as well as the shoals, commemorates French explorer Jean-François de La Pérouse whose crew nearly ran two frigate ships aground the reef in 1786.
The French Frigate Shoals is part of the Northwestern Hawaiian Islands (NWHI), a chain of atolls and small islands northwest of the main Hawaiian Islands, which are home to approximately 13,000 square kilometres of coral reefs (about 70 percent of all coral reefs found in U.S. waters) and to the threatened green sea turtle, seabirds, and the only remaining population of the endangered Hawaiian monk seal.

Located at about midpoint in the NWHI chain, the French Frigate Shoals encompasses the largest coral reef area, over 938 square kilometres, in Hawaii and has the greatest coral diversity in the NWHI, with over forty species of stony corals documented. It also houses more than 600 species of marine invertebrates, more than 150 species of algae, 18 species of sea birds and the largest proportion of endangered Hawaiian monk seals in the NWHI.

The nearly horizontal white strip seen top centre left in the image is Tern Island. The strip is a 1005-metre long runway formed in 1942 by the U.S. military to serve as a fuel stop for aircraft during World War II. Today the U.S. Fish and Wildlife Service maintains a field station there, which is staffed year-round by two permanent employees and a couple volunteers. A sign on the island reads: Population 4, Elevation 6 ft (1.8 m).

Because the animals breeding on Tern Island are sensitive to human disturbance, only specially permitted biologists and researchers are allowed there. Scientists use the infrastructure left behind by the U.S. military as a base for research from which to study all of the animals within the French Frigate Shoals.

In 2000, the French Frigate Shoals became part of the Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve, which was named a national monument in 2006. With more than 362 000 sq km of atolls and reefs, the Northwestern Hawaiian Islands Monument is the largest conservation area in the U.S. and the largest protected marine area in the world. Australia’s Great Barrier Reef Marine Park was previously the world’s largest protected marine area.

ESA’s Proba satellite acquired this image on 9 January 2006 with its Compact High Resolution Imaging Spectrometer (CHRIS), designed to acquire hyperspectral images with a spatial resolution of 17 metres across an area of 13 kilometres.

Friday, August 12, 2011

Lake Malawi, Great Rift Valley, East Africa

This Envisat image features Lake Malawi in the Eastern Rift of the Great Rift Valley, a geological fault system of Southwest Asia and East Africa. The series of lakes in and around the Great Rift Valley is referred to as the 'Great Lakes of Africa'.

Lake Malawi, also known as Lake Nyasa, is the third largest lake in Africa. It occupies one fifth of Malawi (centre, around the lake’s west and south sides) and creates a natural border between Malawi, Tanzania (upper right) and Mozambique (lower right). Most of the land visible on the left belongs to Zambia.

One of the world’s few ancient lakes, Lake Malawi has a unique uninterrupted history. These deep (750 m), isolated waters have shaped a unique diversity of fish that is popular amongst aquarists.

Lake Malawi National Park (at the southern end of the great expanse of Lake Malawi) was designated a Natural World Heritage Site in 1984, with its importance for the study of evolution being compared to that of the finches of the Galapagos Islands.

This image was acquired by Envisat’s Medium Resolution Imaging Spectrometer on 12 October 2010 at a resolution of 300 m.

Thursday, August 11, 2011

Nenets Autonomous Okrug, Russia

This Envisat image features the Nenets Autonomous Okrug region and an icy Pechora Sea in Arctic Northwest Russia.

The Nenets Autonomous Okrug, an administrative region, extends along the Arctic coast, has shorelines on the Barents (blue water in upper left hand corner), White (visible on left side of image) and Kara seas (not visible) and covers some 176 000 sq km of tundra and marshland.

The Pechora Sea, a southeastern extension of the Barents Sea, is located between Kolguyev Island (the round snow-covered depression visible in the upper left hand corner) to the west and the Yugorsky Peninsula (not visible) to the east. With an average depth of 6 m, the sea is relatively shallow.

Kolguyev Island is located in the Barents Sea, a rather deep shelf sea with an average depth around 230 m, and is some 70 km off the mainland. Kanin Peninsula is visible to the southwest of Kolguyev Island.

Pechora River (visible along the right hand side) flows some 1800 km through the region into Pechora Bay. It drains an area of more than 322 000 sq km and forms a large delta at the port of Naryan-Mar, the capital of the Nenets Autonomous Okrug.

This image was acquired by Envisat’s Medium Resolution Imaging Spectrometer (MERIS) instrument on 10 March 2008 working in Full Resolution mode to provide a spatial resolution of 300 metres.

Cool lava, Great Rift Valley, Africa

This Envisat image captures volcanoes dotted across the landscape in Tanzania, including the distinctive Ol Doinyo Lengai, in the Great Rift Valley of East Africa.

The Gelai Volcano (2942 m) is visible at the top, and the Kitumbeine Volcano (1770 m) is southeast of Gelai. Both volcanoes are considered to be extinct – there has been no eruption for at least 10 000 years and they are not expected to erupt again.

The volcanoes are found in the Crater Highlands, a region along the East African Rift in Tanzania. Located at the intersection of the African and Somali tectonic plates, the Crater Highlands rise up from the floors of the Rift Valley and form a lush chain of mountains and volcanoes.

Ol Doinyo Lengai (2886 m), at lower left, is Tanzania’s only active volcano. Uniquely, it is the world’s only active volcano that produces carbonatites – unusual igneous rocks that contain more than 50% carbonate minerals. Furthermore, the type of carbonatite it produces, natrocarbonatite, is particularly rich in sodium.

This type of lava is characterised by a low temperature. Erupting at less than 600°C, Ol Doinyo Lengai is believed to have the coolest lava of any active volcano. For comparison, temperatures as high as 1200°C are known to occur in pyroclastic flows of hot gas and rock.
Several eruptions occurred between September 2007 and April 2008.

Radar images represent surface backscatter rather than reflected light, so there is no colour in a standard radar image. This image was created by combining three Envisat Advanced Synthetic Aperture Radar acquisitions (3 February 2010, 30 December 2009 and 25 November 2009) of the same area. The colours result from changes in the surface between acquisitions.

Wednesday, August 10, 2011

Vilamatsa, Madagascar

The north-western area of Madagascar – the fourth largest island in the world – is seen in this Proba image.

Madagascar is located in the Indian Ocean, off the eastern coast of Africa. The island was once attached to the African mainland, but broke away more than 150 million years ago.
The island nation became a French colony in 1896, and regained its independence in 1960. Along with Malagasy, French remains one of the country’s two official languages.

Madagascar is the home of five percent of the world's plant and animal species. According to the World Wildlife Fund (WWF), 98 percent of Madagascar's land mammals, 92 percent of its reptiles, 68 percent of its plants and 41 percent of its bird species exist nowhere else on Earth.

Recently highlighted in the animated comedy ‘Madagascar’, furry, tree-hopping lemurs are endemic to the island. Although they appear to resemble felines or canines, lemurs are primates – as are monkeys, apes and humans.

There are approximately 33 different species of lemurs in Madagascar, and they are considered the most endangered primates in the world. Loss of habitat through deforestation is believed to pose the biggest threat to the island’s flora and fauna.

Madagascar is recognised as one of the highest priority hotspots with numerous international conservation organizations and the Malagasy government working together to preserve the island’s unique biodiversity.

This image was acquired on 16 September 2004 by the Compact High Resolution Imaging Spectrometer (CHRIS). Built by UK-based Sira Technology, CHRIS is the main payload on ESA's Proba micro satellite, designed to acquire hyperspectral images with a spatial resolution of 18 metres across an area of 14 kilometres.

The size of a washing machine, Proba was originally launched in 2001 as a technology demonstrator, but is now operated as an ESA Earth Observation Third Party Mission.