El Hierro Volcano research improves algorithms used by EO satellites

Image taken by the satellite WorldView-2 in October 2011. 

The bright green waters indicate high concentrations of volcanic material flowing from the brown zone, which is where the volcano is located. 

On the right, the ‘diffuse attenuation coefficient’ has been applied, this is an indicator of the water roughness level. 

The areas shaded in black are clouds. 

Credit: Institute of Oceanography and Global Change (ULPGC)

Information provided by satellites on the amount of chlorophyll-A and the roughness of the sea following the eruption of the underwater volcano off the island of El Hierro (Spain) did not coincide with the actual data collected in situ by vessels carrying out oceanographic studies.

The models have been corrected by researchers at the University of Las Palmas de Gran Canaria, who have for the first time processed very high resolution images of this kind of natural phenomenon captured from space.

The image of the Canary Islands which won the prize this year of NASA's Earth Observatory was captured by one it its satellites, 'Terra', with the Moderate Resolution Imaging Spectro-radiometer (MODIS) instrument.

This sensor also travels in the US space agency's satellite 'Aqua' as well as alongside the Medium Resolution Imaging Spectrometer (MERIS) in the European Space Agency's satellite Envisat, and they have helped to understand the evolution of the underwater volcano which emerged in 2011 beneath the waters surrounding the island El Hierro, in the Canary Islands.

However, the information supplied by MODIS and MERIS was incorrect with regard to certain marine parameters, according to measurements taken in situ by oceanographic research vessels of the Spanish Institute of Oceanography (IEO).

This has now been confirmed by researchers of the University of Las Palmas de Gran Canaria (ULPGC) in a study published by the 'International Journal of Applied Earth Observation and Geoinformation'.

"The algorithms used with the data from the NASA and ESA satellites made mistakes when determining the concentration of chlorophyll-A (a variable that indicates the biological productivity in marine ecosystems) as it showed concentrations that were greater than actual ones as measured by the research ships," explained Francisco Eugenio, co-author of the study and researcher at the Institute of Oceanography and Global Change at the ULPGC, to SINC.

Members of this institute have developed new mathematical algorithms that correct the incongruities detected with chlorophyll-A as well as what is known as the 'diffuse attenuation coefficient' - an indicator of the sea turbulence in terms of dissolved material.

This parameter had also been over-estimated when applied to the data from the satellites.

"In any case, the images processed from these remote sensors have proven to be a very powerful tool for monitoring effects associated with underwater volcanic activity, such as the change of colour of the water, the presence of floating matter and volcanic plumes," Eugenio underlined.

The researcher also pointed out that, for the first time, very high resolution images have been obtained to follow this kind of geological phenomenon.

These are the images obtained from the private satellite Worldview-2, which has a pan-chromatic resolution of 46 centimetres -in black and white- and 1.85 metres in 8 multi-spectral bands. New algorithms have also been used with these.

In the case of these images, as with the low-resolution images obtained from MODIS and MERIS, the researchers have been able to work out the chronology of the atmospheric, oceanographic and biological parameters in the ocean since the volcano erupted three years ago at a depth of 300 metres below the ocean surface.

This data has been supplemented with the samples retrieved from all round the island in the project called 'Vulcano', which was most recently conducted last March.

For its part, the IEO's underwater robot Lirupos 2000 has also captured the growth of the underwater volcano's structure and the rapid rate at which the marine ecosystem is recolonizing the area.

"Currently, the volcano's main crater is at the same depth as it was in October 2013, which is 88 metres below the ocean surface," explains Eugenio.

He goes on to confirm: "The waters around El Hierro are fine, and, with the exception of a small area within a 200-metre radius around the main crater, no physical or chemical anomalies have been detected at any point around the periphery of the island, from the ocean surface to depths of 1,200 metres."

More information: F. Eugenio, J. Martin, J. Marcello, E. Fraile-Nuez, "Environmental monitoring of El Hierro Island submarine volcano, by combining low and high resolution satellite imagery," International Journal of Applied Earth Observation and Geoinformation, Volume 29, June 2014, Pages 53-66, ISSN 0303-2434, dx.doi.org/10.1016/j.jag.2013.12.009.

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 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: 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.

ESA MERIS Earth from Space: Eire Electric blue blooms

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.

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), which acquired this image on 23 May 2010 at a resolution of 300 m.

Credits: ESA

ESA Observing the Earth from Space: Plankton Bloom arrives in Scandinavia

ESA - Observing the Earth - Earth from Space: Plankton arrives in Scandinavia

Envisat captures a crescent-shaped string of plankton in the North Sea weaving through the Scandinavian region.

Norway (left) and Sweden (right), part of the Scandinavian Peninsula, are visible at the top, and Denmark is at bottom right.

The emerald green lake seen in Sweden is Vänern, the country’s largest.

The green water around Denmark is due to sediments being transported in the water. Also visible (image centre) is Norway’s second largest fjord, Hardangerfjord. Envisat's MERIS acquired this image on 3 May 2010 at a resolution of 300 m.

Credits: ESA

Gulf of Mexico Oil Spill: Loop Current and the Gulf Stream

This Envisat image shows the Straits of Florida, the area where the Loop Current flows eastward out of the Gulf of Mexico (visible west of Florida) before joining the Gulf Stream and flowing along the eastern coastlines of the US and Newfoundland.

This image was acquired by Envisat’s Medium Resolution Imaging Spectrometer (MERIS) on 1 April 2010 at a resolution of 300 m.

click here for more info on this issue .

Credits: ESA

ESA ENVISAT MERIS Image: New Zealand and Cook Strait

Credits: ESA

This Envisat image captures New Zealand's North and South Islands, separated by the Cook Strait.

Named after James Cook, who in 1770 was the first European to sail through it, the Cook Strait connects the Tasman Sea to the west with the South Pacific Ocean to the east.

This image was acquired on 8 March 2010 by Envisat's Medium Resolution Imaging Spectrometer (MERIS).

Background Info

At its narrowest, it is just 23 km wide – so on a clear day it is possible to see across the strait. However, the Cook Strait is also renowned for being one of the roughest and most unpredictable stretches of water in the world.

As a result of New Zealand's latitude, the country lies in the path of the westerly wind belt known as the Roaring Forties. Since the strait is the only gap between the mountainous two islands, it acts as a huge wind tunnel, whipping up treacherous seas.

In addition, the tidal flow through Cook Strait is unusual. The tide is out of phase, which means when it is high tide on one side it is low on the other, resulting in strong currents in the middle.

New Zealand comprises many islands, though the North and South Islands are the largest landmasses. The image shows that the northerly part of the South Island is, in fact, further north that the south of the North Island. The South Island is the larger of these two landmasses and along its length gives rise to the Southern Alps, where the highest peak, Mount Cook, reaches 3754 metres. The North Island is less mountainous but more volcanic.

To read more on ESA Envisat: MODIS and New Zealand, Click here on the link

ESA ENVISAT MERIS Image: Sea Ice of Okhotsk

This Envisat image captures sea ice in the Sea of Okhotsk off the northeastern coast of Russia’s Sakhalin Island (top left) and the northern tip of Japan’s Hokkaido Island (bottom left).

Sea ice began forming in the northern area over the Sea of Okhotsk in November 2009. Since then, it extended down to about 30 km off the northern coast of Hokkaido and has likely reached its maximum.

Sakhalin is separated from the east coast of Russia by the narrow Strait of Tartary and from the northern tip of Japan by the Strait of La Pérouse, which appears to be ice-free.

Sitting astride an active seismic zone, Sakhalin is prone to earthquakes that can trigger mudslides. The formal penal colony is covered in ice during the winter months, and its surrounding cool, fertile waters support enormous fisheries. But that’s not all; an estimated 45 billion barrels of oil equivalent are believed to lie beneath the icy seas off its shores.

Hokkaido is the northernmost and second largest island of Japan’s four main islands. The three islands visible northeast of Hokkaido belong to the Kuril Island chain, which comprises 22 main islands and some 30 smaller islets.

Stretching for 1250 km northwards from Hokkaido to the southern tip of Russia's Kamchatka Peninsula (not visible), the Kuril Islands form a boundary between the Sea of Okhotsk and the Pacific Ocean (bottom right).

This image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument on 9 March 2010, working in Full Resolution mode to provide a spatial resolution of 300 m.