ESA ENVISAT: De-orbiting and space debris threat from giant satellite

Artist's impression of Envisat orbiting the Earth. Credits: ESA

Physics students at the University of Leicester have pointed out that ESA's huge observational satellite Envisat, which lost contact with Earth in 2012, could potentially pose a space debris threat to the Earth.

What's more, the task of bringing the satellite back to Earth may be too costly and complex to be feasible, according to their final year paper for the Journal of Physics Special Topics, a peer-reviewed student journal run by Leicester University's Department of Physics and Astronomy.

Envisat, an £1.8 billion, 9 metre-long behemoth, was launched by the European Space Agency (ESA) in 2002, and used ten sophisticated sensors to observe and monitor Earth's land, atmosphere, oceans and ice caps.

However, ESA lost contact with the satellite in April, 2012 and declared the end of the mission soon after.

The satellite now orbits the Earth free from human control at an altitude of 790km, where the amount of space debris around the planet is greatest.

This means there is a greater chance of collision with other satellites and debris during the 150 years it is expected to remain in space.

Each year, two objects are expected to pass Envisat to within about 200m and other spacecraft have had to move out of Envisat's path.

It is possible – though unlikely - that a collision with Envisat could lead to a chain reaction effect, known as the Kessler Syndrome, where a cloud of fast-moving debris causes other collisions with orbiting bodies around the Earth.

This would not be good news for the many essential satellites and spacecraft in orbit.

It could also make it difficult for future space missions to pass through the region of Envisat's altitude, if the region becomes congested with space debris.

The fourth-year MPhys students' paper, 'De-orbiting Envisat', suggests that around 140kg of fuel would be required to move the satellite to a point where it would naturally return to Earth within 25 years.

Based on the object's cross-sectional area and its mass, the students calculated that the satellite would need to be moved to an altitude of 700km from its current position in order to return to the planet in 25 years.

The students calculated that the energy required to move the satellite 90km closer to the Earth was 2.7 billion joules, equivalent to an extra 143.1kg of hydrazine fuel.

This could be quite feasible, according to the students, if two of the craft's 80kg fuel tanks were replaced.

But actually getting this fuel to the satellite in orbit would be a pretty tall order due to the costs involved of such a mission – which has never been attempted for a satellite which wasn't designed to be refuelled.

More information: "De-orbiting Envisat." K. Raymer, T. Morris, O. Youle, B. Jordan, Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH. physics.le.ac.uk/journals

ESA ENVISAT Radar Image: Western Uganda lakes and mountains

Lakes and mountains of Western Uganda are captured in this Envisat radar image.

The area pictured is part of the Albertine Rift, a branch of the East African Rift where the Somali Plate is splitting away from the rest of the continent.

ESA Envisat Image: Indonesian Volcanic Islands

The tropical islands of Bali, Lombok and Sumbawa tower above the waves in this image from the European Space Agency's Envisat satellite.

All three islands are volcanoes, part of the Sunda Arc.

This image is a compilation of three passes by Envisat on June 20, Aug. 19 and Dec. 17, 2011.

CREDIT: European Space Agency

The tropical islands of Bali, Lombok and Sumbawa tower above the waves in this image from the European Space Agency's Envisat satellite.

The island on the west, or left side of the picture, is Bali, one of Indonesia's main tourist destinations.

The island's central mountains include peaks that reach 9,800 feet (3,000 meters), including an active volcano on the right side of the island.

The central island is Lombok. To the east is Sumbawa island, dominated by mountainous terrain and home to Mount Tambora, an active volcano.

Mount Tambora's last major eruption was in 1815, killing more than 70,000 people and cooling much of the Northern Hemisphere, causing "the year without a summer."

The eruption is one of the biggest and deadliest in recorded history.

All three islands sit over the submarine Java trench, where one tectonic plate slides under another.

As the plate descends into Earth's mantle, fluids from the crust move into the mantle rock, letting it melt more easily, and the melted rock rises upwards like lava lamp blobs.

These lava blobs punch through the crust, forming volcanoes.

ESA Envisat Image: Juruá River in the Amazon rainforest

Snaking River

Credit: European Space Agency

The Juruá River snakes slowly through the half-flooded Amazon rainforest in western Brazil, leaving free-standing oxbow lakes in its wake, which form when a river changes course as it meanders through a floodplain.

The Juruá is the most winding river in the Amazon basin and one of the Amazon River's longest tributaries, exceeding 2,040 miles (3,283 kilometers) in length. Tropical rainforests have some of the largest rivers in the world because of the tremendous amount of precipitation their watersheds receive.

ESA Envisat: Paraná River in Brazil As Seen From Space

The Paraná River cuts through this image of southern Brazil from the Envisat satellite.

Credit ESA/Envisat

In the area pictured, the river marks the borders of the Brazilian states of Mato Grosso do Sul to the north and west, Sao Paulo to the east and Paraná to the south.

The river along with its tributaries creates a massive watershed that spreads throughout much of the south central part of the continent. Agricultural structures are evident in the surrounding land. The area is known as a large producer of coffee.

Click here to play the ESA/Envisat video of Parana River

Near the centre of the image, smoke from a fire was captured blowing southwest from its source. Major fires are visible from space - satellites detect not only the smoke billowing from major conflagrations but also the burn scars left in their wake and even the fires themselves - appearing as hotspots when scanning Earth's surface in thermal-infrared wavelengths.

Envisat's Advanced Along-Track Scanning Radiometer was like a thermometer, measuring thermal-infrared radiation to take the temperature of Earth's land and sea surfaces.

Prior to the end of the Envisat mission in April, the radiometer data contributed to the ATSR World Fire Atlas.

Temperatures exceeding about 39oC were classed as burning fires by the instrument, which was capable of detecting fires as small as gas flares from industrial sites because of their high temperature. Fires are detected best during local night, when the surrounding land is cooler.

This image was acquired by the MERIS instrument on Envisat on 19 March.

The Image of the Week is featured on ESA Web-TV, broadcast online every Friday at 10:00 CEST.

ESA: Amazon Rainforest Jurua river - images

This image from the Envisat satellite shows the Juruá River snaking through the Amazon rainforest in western Brazil. 

Along the river’s main course are free-standing ‘oxbow lakes’, formed when a river changes course.

This image is a compilation of three images from Envisat’s radar, acquired on 2 January, 1 February and 3 March 2012. 

The individual images are each assigned a colour – red, green and blue – and when combined, reveal changes in the surface between Envisat’s passes.

Credits: ESA

This image from the Envisat satellite shows the Jurua River snaking through the Amazon rainforest in western Brazil. The Jurua is one of the longest tributaries of the Amazon River, flowing slowly through the half-flooded forest country it traverses in the Amazon Basin.

Along the river's main course are free-standing 'oxbow lakes', formed when a river changes course.
Tropical rainforests have some of the largest rivers in the world because of the tremendous amount of precipitation their watersheds receive.

Given its size, remote sensing is the best way to study the Amazon Basin on a large scale - especially for assessing the extent and damage due to deforestation.

This image is a compilation of three images from Envisat's radar, acquired on 2 January, 1 February and 3 March 2012. The individual images are each assigned a colour - red, green and blue - and when combined, reveal changes in the surface between Envisat's passes.

Satellite radar data can be exploited to map forest height, 3D forest structure and their natural or anthropogenic disturbance with high spatial resolution and accuracy.

Since forests assist in removing carbon dioxide from the atmosphere, this could prove to be an important tool for assessing carbon stocks and monitoring our planet's resources.

Envisat has recently been experiencing technical difficulties. Following ten years of service, the satellite stopped sending data to Earth on 8 April. ESA's mission control is working to re-establish contact with the satellite.

Images on ESA Portal

ESA Envisat services interrupted

Envisat’s Medium Resolution Imaging Spectrometer (MERIS) captured this image on 8 April 2012 at 13:05 CEST. 

The image was transmitted in Ka-band to ESA/ESRIN though direct transmission via Artemis, the ESA Data Relay satellite.

The image, which is of nominal quality, shows Portugal and Spain. 

It is the last Envisat data transmitted via Ka-band before the communication anomaly affected the Envisat satellite.

Credits: ESA

After 10 years of service, Envisat has stopped sending data to Earth. ESA’s mission control is working to re-establish contact with the satellite.

Although this landmark mission has been in orbit twice as long as it was designed for, ESA hopes to keep the satellite in service until the launch of the successor Sentinel missions.

The first sign that there was a problem came on 8 April when contact with the satellite was unexpectedly lost, preventing the reception of any data as it passed over the Kiruna ground station in Sweden.

ESA’s mission control team declared a spacecraft emergency and immediately called for support from additional ESA tracking stations around the world. A team of operations and flight dynamics specialists and engineers was quickly assembled.

In a concerted effort, the recovery team, which included experts from industry, spent the next days trying to re-establish communications with the satellite.

While it is known that Envisat remains in a stable orbit around Earth, efforts to resume contact with the satellite have, so far, not been successful.

As is standard practice, an anomaly review board is investigating the cause for the break in communications.

Envisat has exceeded its planned life of five years by far. Since it was launched in 2002, this remarkable satellite has orbited Earth more than 50 000 times delivering thousands of images and a wealth of data to study and understand our changing planet, establishing itself as a landmark success in observing Earth from space.

As the world’s most complex Earth observation satellite, Envisat carries 10 sophisticated instruments that have provided key information about our land, oceans, ice and atmosphere. Combined with data from the ERS missions since 1991, Envisat has provided precise measurements on climate change over the last 20 years.

More than 4000 projects in over 70 countries have been supported with Envisat data. Data in the archives will continue to be available for users.

A contingency agreement with the Canadian Space Agency on Radarsat will be activated to allow a continuity in service. This will allow contracts to be served to some of the user requirements, if the problem with Envisat persists.

ESA ENVISAT Image: Gobi Desert Image

This ESA Envisat radar image features the terrain of the Gobi Desert, which stretches across vast areas of the Mongolian People's Republic and the land claimed by land-grab China to be the Inner Mongolian Autonomous Region of China.

Envisat’s Advanced Synthetic Aperture Radar (ASAR) acquired this image.

Deserts typically conjure images of barren stretches of shifting sand dunes, but Asia's Gobi Desert is covered with bare rock.

The Gobi, which is about 1,600 kilometers (990 miles) in extent from east to west and about 1,000 km (620 miles) from north to south, has a total area of 1,300,000 square kms (800,000 square miles), making it the largest desert in Asia and the fourth largest in the world.

The desert stretches across vast areas of the Mongolian People's Republic and the, so called, Inner Mongolian Autonomous Region, claimed by land grabbing China.

The Gobi 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, according to a European Space Agency (ESA) statement.

ESA ENVISAT Image: Bali, Lombok, and Sumbawa: Where Worlds Collide

This image from the Envisat satellite is dominated by the Indonesian islands of Bali, Lombok and Sumbawa.

All three are part of the volcanic Sunda Arc along the submarine Java trench, where two tectonic plates are moving towards one another, and one slides under the other.

This tectonic deformation along the Java trench caused the 2004 Indian Ocean earthquake and subsequent tsunami.

To the west is Bali, one of Indonesia's main tourist destinations. The island's central mountains include peaks that reach over 3000 m, including an active volcano visible on the right side of the island.

Strong reflections of the radar signal used to produce this image appear like specks of light. They are mainly detectable in the southern part of the island, and are particularly concentrated around the provincial capital city of Denpasar.

This is the typical appearance of built-up areas in radar images, owing to the multiple reflection of the radar beam by buildings and especially metal constructions.

In the centre of the image is Lombok. Similar to Bali, we can see multiple reflections concentrated around the city of Mataram.

Varying colours stretch across the island's lowlands, which are highly cultivated, depicting changes in the land.

Sumbawa island lies to the east, dominated by mountainous terrain. This is also home to Mount Tambora, an active volcano.

In 1815, its massive eruption caused heavy ash falls that ruined local agriculture and even affected much of the Northern Hemisphere.

The deaths of over 70 000 people are attributed to this event. This image is a compilation of three passes by Envisat's radar on 20 June, 19 August and 17 December 2011.

Each is assigned a colour (red, green and blue) and combined to produce this representation. The colours reveal changes in the surface between Envisat's passes.

ESA Envisat: Earth from Space: Historical view

West Africa’s coast along the Atlantic Ocean is pictured in this first image from Envisat’s MERIS instrument nearly a decade ago.

This week, Envisat celebrated ten years in orbit. The Medium Resolution Imaging Spectrometer (MERIS) on board the satellite was developed to measure sea colour in oceans and coastal areas, although it has been used for a variety of additional applications over the years.

Happy Birthday ESA's ENVISAT (Video)

Envisat carries ten sensors, collecting imagery and other data on Earth’s land, oceans, atmosphere, temperature and ice cover.

The first batch of data from the satellite in March 2002 was acquired via the Kiruna station in Sweden and processed at ESA’s ESRIN establishment in Italy and other centres throughout Europe.

In this first image from MERIS on 22 March 2002, a very dry desert directly borders the ocean teeming with life. To the south, a high concentration of phytoplankton was detected along the coasts of Senegal, the Gambia and Guinea-Bissau.

Small, single-celled phytoplankton play a key role in the marine food chain. They convert sunlight, carbon dioxide and nutrients into carbohydrates on which nearly all life in the ocean depends.

In most parts of Earth’s oceans, phytoplankton concentration is extremely low. However, in ‘upwelling areas’ like the one pictured here, the ocean becomes rich in minerals from the mixing of surface waters with deeper waters.

The most important fishing grounds can be found in these upwelling areas. Climate change has an effect on the intensity and geographical position of these areas, which, in turn, has important consequences for the fishing industries and those who depend on them.

Also evident in this image is the transition from the dry desert lands in the north through the savannah and to tropical vegetation in the south, which receives more rainfall. MERIS can monitor land use that leads to increased erosion and soil loss.

The Image of the Week is featured on ESA Web-TV, broadcast online every Friday at 10:00 CET.

The UFO In Baltic Sea

Envisat Medium Resolution Imaging Spectrometer (MERIS) satellite image acquired July 11, 2010 shows blue-green algae blooms in the Baltic Sea.

The term "Algae bloom" is used to describe the multiplying of phytoplankton, microscopic marine plants that drift on or near the surface of the sea. 

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

Germany, Sweden, Estonia, Latvia, Lithuania, Russia and Poland are pictured bordering the sea.

(Photo: REUTERS/European Space Agency/)

 
In 2011, an extraordinary circular object was seen on the surface of the Baltic Sea by a group of stranded ship hunters. This year, they claimed again that they have witnessed another strange object with a disc-like shape around 200 meters away- from the area where they first saw the same kind of thing.

The leader of the team, Peter Lindberg, joked that the first thing they have discovered 300 feet below the sea surface might be a UFO, or an unidentified flying object, when interviewed by CNN.

The first bizarre object that was discovered June last year has a diameter of 195 feet. Believers thought of it as a stranded UFO, which had smashed into the sea leaving behind a trail of damage about 900 feet. The story regarding this so-called UFO was exposed at News.com.au.

CNN news revealed how the group found out about the objects.

The hunters were using an imaging technique that tracks down and magnetize a sonar "towfish." The towfish actually appears sideways underwater. They placed the device at the back of the boat, where it suitably produces a sound that echoes to map underwater.

The Baltic Sea is like a breeding ground where you can typically discover retrieved objects. Ardreas Olsson, a sonar expert, said they have identified 20,000 salvaged objects mostly stranded ships in the Baltic Sea. Olsson thinks that there could be over 100,000 things to discover underwater. He's excited to encounter more discoveries.

UFO believers are for sure more than excited to hear updates about the new found object.

ESA ENVISAT & ERS Satellites detect abundance of fresh water in the Arctic

ESA satellites show that a large dome of fresh water has been building up in the Arctic Ocean over the last 15 years.

A change in wind direction could cause the water to spill into the north Atlantic, cooling Europe.

The results are remarkable: since 2002, the sea surface in the studied area has risen by about 15 cm, and the volume of fresh water has increased by some 8000 cubic km – around 10% of all the fresh water in the Arctic Ocean.

Researchers from the Centre for Polar Observation and Modelling (CPOM) at University College London and the UK’s National Oceanography Centre used data from ESA’s ERS-2 and Envisat satellites to measure sea-surface height over the western Arctic from 1995 to 2010.

The results were published yesterday in the online version of the scientific journal, Nature Geoscience.

	Mean sea surface

The scientists conclude that the dome could be a result of strong Arctic winds accelerating a large ocean circulation known as the Beaufort Gyre, causing the sea surface to bulge.

A change in the direction of the wind would cause the fresh water to spill into the rest of the Arctic Ocean and even reach the north Atlantic.

This could slow a key ocean current, stemming from the Gulf Stream, and subsequently cool Europe.

This current keeps the continent relatively mild compared to other areas at similar latitudes.

“When we looked at our data on a year-to-year basis, we noticed that the changes in the sea surface height did not always follow what the wind was doing, so we thought about reasons why this might happen,” said Katharine Giles, CPOM research fellow and lead author of the study.

“One idea is that sea ice forms a barrier between the atmosphere and the ocean. So as the sea ice cover changes, the effect of the wind on the ocean might also change.

“Our next step is to look into how changes in the sea ice cover might affect the coupling between the atmosphere and the ocean in more detail to see if we can confirm this idea.”

Sea ice can be measured by different types of satellite data. Radar altimeters on satellites such as the two used in the study, Envisat and ERS-2, can be particularly useful when observing inaccessible areas like the Arctic.

ESA ENVISAT: A southern summer bloom

In this ESA Envisat image, a phytoplankton bloom swirls a figure-of-8 in the South Atlantic Ocean about 600 km east of the Falkland Islands.

During this period in the southern hemisphere, the ocean becomes rich in minerals from the mixing of surface waters with deeper waters.

Phytoplankton depend on these minerals, making blooms like this common in the spring and summer.

These microscopic organisms are the base of the marine food chain, and play a huge role in the removal of carbon dioxide from the atmosphere and the production of oxygen in the oceans.

By helping to regulate the carbon cycle, phytoplankton are important to the global climate system.

Different types and quantities of phytoplankton exhibit different colours, such as the blues and greens in this image.

Earth-observing satellites like Envisat can monitor these algal blooms. Once a bloom begins, an ocean colour sensor can make an initial identification of its chlorophyll pigment, and therefore its species and toxicity.

Since the phytoplankton are sensitive to environmental changes, it is important to monitor and model them for climate change calculations and to identify potentially harmful blooms.

Envisat’s MERIS instrument acquired this image on 2 December 2011 at a resolution of 300 m.

ESA ENVISAT Image: Arid Arabia

This Envisat image, acquired on 28 October 2011, shows central Saudi Arabia on the arid Arabian Peninsula. 

The area pictured is on the central plateau, Nejd, which slopes downwards from west to east. 

The dark circle near the centre of the image is the capital city of Riyadh, the nation’s legislative, financial administrative, diplomatic and commercial hub.

Credits: ESA

ESA ENVISAT Image: Icy waters of Ilulissat Fjord

This Envisat image, acquired on 21 July 2011, shows part of Greenland’s west coast – home to one of the fastest and most active glaciers in the world, Sermeq Kujalleq. 

At the centre of the image the glacier’s sea mouth is visible: the Ilulissat fjord, with icebergs bursting out from it and speckling the surrounding waters.

Credits: ESA

ESA ENVISAT: Aegean islands

This Envisat image is dominated by the island of Crete separating the Aegean and Libyan Seas in the eastern Mediterranean.

At the top of the image we can see the southern portion of the Cyclades island group, including the islands of Milos, Ios, Anafi and Santorini.

This image is a compilation of three passes by Envisat’s radar on 11 December 2010, 10 January and 11 March 2011.

Each is assigned a colour (red, green and blue) and combined to produce this representation.

New colours reveal changes in the surface between Envisat’s passes.

For a high resolution version of this image, please visit: www.esa.int/esaEO/SEMLH2GURTG_index_0.html

Credits: ESA

ESA ENVISAT Image: Spitrsbergen, Norway's Glacier island

Spitsbergen, Norway’s largest island, is pictured in this image, acquired on 6 September 2011 by Envisat’s Advanced Synthetic Aperture Radar (ASAR). 

Bordered by the Arctic Ocean to its north and the Greenland Sea to its west, Spitsbergen is the largest and only permanently populated island of the Svalbard archipelago.

Credits: ESA

Bordered by the Arctic Ocean to its north and the Greenland Sea to its west, Spitsbergen is the largest and only permanently populated island of the Svalbard archipelago.

The island has many glaciers, mountains and fjords – long inlets created by glacial activity.

Because of its high latitude, average summer temperatures are between 4 °C and 6 °C, while winters drop to around −20 °C. The North Atlantic Current, however, gives Spitsbergen significantly higher temperatures than other places at the same latitude.

Arctic foxes, reindeer and polar bears roam the land here. The surrounding waters are home to whales, dolphins and walruses.

This image was acquired on 6 September by Envisat’s Advanced Synthetic Aperture Radar. 

NASA, ESA, JAXA Maps Antarctic Ice Flows

First complete map of the speed and direction of ice flow in Antarctica, derived from radar interferometric data from the Japan Aerospace Exploration Agency's ALOS PALSAR, the European Space Agency's Envisat ASAR and ERS-1/2, and the Canadian Space Agency's RADARSAT-2 spacecraft.

The colour-coded satellite data are overlaid on a mosaic of Antarctica created with data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra spacecraft.

Pixel spacing is 984 feet (300 meters). The thick black lines delineate major ice divides. Subglacial lakes in Antarctica's interior are also outlined in black. Thick black lines along the coast indicate ice sheet grounding lines.

Image credit: NASA/JPL-Caltech/UCI

ESA ENVISAT Image: Qeshm Island, Jewel of the Persian Gulf

This Envisat image features the largest island in the Persian Gulf: Iran’s Qeshm Island.

This long thin island lies just a few kilometres off the Iranian coast near the narrow Strait of Hormuz.

The Straits of Hormuz separate the Persian Gulf to the west and the Gulf of Oman to the southeast.

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 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.

Credits: ESA

ESA ENVISAT - Record loss of ozone over Arctic

Average Arctic total ozone for the month of March between 1979 and 2011, based on assimilated observations of several satellite instruments: TOMS, SBUV, GOME, SCIAMACHY, OMI, GOME-2.Credits: KNMI

ESA’s Envisat satellite has measured record low levels of ozone over the Euro-Atlantic sector of the northern hemisphere during March.

This record low was caused by unusually strong winds, known as the polar vortex, which isolated the atmospheric mass over the North Pole and prevented it from mixing with air in the mid-latitudes.
This led to very low temperatures and created conditions similar to those that occur every southern hemisphere winter over the Antarctic.

	Arctic temperature field

As March sunlight hit this cold air mass it released chlorine and bromine atoms – ozone-destroying gases that originate from chlorofluorocarbons (CFCs) and break ozone down into individual oxygen molecules – predominantly in the lower stratosphere, around 20 km above the surface.


Ozone is a protective atmospheric layer found at around 25 km altitude that acts as a sunlight filter shielding life on Earth from harmful ultraviolet rays, which can harm marine life and increase the risk of skin cancer and cataracts.
ESA - Observing the Earth - Record loss of ozone over Arctic - images