Category: Earth Observation

Hurricanes are one of those forces of nature that can only fully be captured by satellite imagery. For Hurricane Frances, currently thundering towards the United States coast, ESA’s Envisat is going one better, peering through the hurricane from top to bottom, even helping to ‘see’ under the waves to map hidden forces powering the storm.

As its 235-km-per-hour winds passed the Bahamas, Frances was heading for landfall on the Florida coast some time on Saturday, and three quarters of a million Americans are in the process of evacuating their homes. To wait and watch for Frances might be suicidal for human beings, but space-based observers such as Envisat observe its passage without danger.

“Because of Envisat’s multi-sensor capability, we can slice right through the hurricane with just a single satellite,” explained Jos? Achache, ESA Director of Earth Observation Programmes.

“Effectively Frances is taken apart for meteorologists to study. The data returned by Envisat includes cloud structure and height at the top of the hurricane, wind and wave fields at the bottom, sea surface temperature and even sea height anomalies indicative of upper ocean thermal conditions that influence its intensity.”

Important processes occur at a range of altitudes and locations throughout a hurricane – basically a large powerful storm centred around a zone of extreme low pressure.

Strong low-level surface winds and bands of intense precipitation combine with strong updrafts and outflows of moist air at higher altitudes, with energy released as rainy thunderstorms. Until now, the only reliable source of such high-resolution measurements at different altitudes was from aircraft flown directly through the hurricane.

Envisat carries both optical and radar instruments, enabling researchers to observe high-atmosphere cloud structure and pressure in the visible and infrared spectrum, while at around the same time using radar backscatter to measure roughness of the sea surface and so derive the wind fields just over it.

Those winds converging on the low-pressure eye of the storm are what ultimately determine the spiralling cloud patterns that are characteristic of a hurricane.

Florida-based scientists have begun to take advantage of this unique single-spacecraft combination of instruments ? the Medium Resolution Imaging Spectrometer (MERIS) and Advanced Synthetic Aperture Radar (ASAR) ? as hurricane season gets into full swing.

The University of Miami’s Centre for Southeastern Tropical Advanced Remote Sensing (CSTARS) ground station has an agreement to acquire ASAR and MERIS data direct from Envisat, with ERS-2 wind scatterometer data set to follow in the near future. Their access to Envisat data has come just as the second hurricane in less than a month is heading towards the Florida coast.

“With MERIS and ASAR, Envisat can image both the ocean and atmosphere pretty much simultaneously, which is a very useful capability during hurricane season,” said Hans Graber, Professor of Applied Marine Physics at the University of Miami and Co-Director of CSTARS.

While MERIS returns detail on the swirling clouds at the top of the hurricane, ASAR pierces right through the clouds to show the wind-wracked face of the sea beneath the storm.

“Specifically in terms of Frances, the eye of the hurricane seems to be rolling a lot right now from the top of the clouds, looking quite unstable, the information from an ASAR image should help localise its size and position on the ocean,” Graber said. “And wind fields around the eye wall can be derived from ASAR data ? right now all we have to go on are measurements from the hurricane hunter planes that fly right through the storm.”

Simultaneous MERIS and ASAR acquisitions are planned for Friday by CSTARS, even as the storm comes closer to predicted landfall the following morning.

“Our current activity is along the lines of a shakedown ? we’re investigating how this can be used,” added Graber. “Our final goal is to get this working on an operational basis during hurricane season. We have a deal to use radar data from the Canadian Space Agency, and also have access to other satellite resources for high temporal coverage of the affected region.

“The potential is there to extract a large amount of useful information which can help the US National Hurricane Center increase the accuracy of their hurricane predictions and reduce danger to the public.”

Another instrument aboard Envisat is being used to take the temperature of Frances, both down at the surface of the ocean and at the heights of its towering clouds.

Water temperatures are the main underlying energy reservoir powering Frances; together with the correct atmospheric conditions, they need to exceed 26?C in order to form and maintain a tropical cyclone. Envisat’s Advanced Along Track Scanning Radiometer (AATSR) works like a space-based thermometer, acquiring the temperature of the sea surface down to a fraction of a degree.

Meanwhile AATSR also returns useful atmospheric data, measuring the temperature of the top of hurricane clouds ? the higher into the atmosphere they extend, the colder they are – and also deriving their ice content.

“We produced a combined AATSR sea surface temperature and cloud top temperature image, which shows the sea surface temperature to be as high as 29?C in the area,” remarked Carsten Brockmann of Brockmann Consult, a German company processing both MERIS and AATSR hurricane imagery. “This two-sensor combination gives meteorologists a lot of information to help them understand the dynamics of the hurricane and better predict its development.”

AATSR information can be correlated with MERIS data cloud height and development to gain a good estimate of the hurricane’s precipitation potential, and improve understanding of how this relates to its overall intensity. Condensation of water vapour releases latent heat, which warms the vicinity of the hurricane eye. This in turn evaporates more surface water and feeds the heat engine powering the hurricane.

Studying hidden depths that fuel the storm
The thermal energy of warm water, which partly powers a hurricane, is known as tropical cyclone heat potential (TCHP).

Oceanic features, such as warm core rings, eddies, and the Gulf Stream, represent a source of enhanced heat fluxes to the atmosphere that may cause the strengthening of tropical cyclones, such as hurricanes.

Warm waters may extend to at least 100 meters beneath the surface in many of these oceanic features, representing waters of very high heat content. Several hurricanes have intensified when their tracks pass over eddies or other masses of warm water with high TCHP values.

For example, in 1995 Hurricane Opal suddenly intensified in the Gulf of Mexico after passing over a warm ring with TCHP values of up to six times the threshold to sustain a tropical cyclone.

Previously, researchers used sea surface temperature alone to estimate the role of the upper ocean thermal conditions on hurricane intensification. The problem with this is that the sea surface temperature measured by AATSR or comparable satellite instruments may not by themselves show these warm upper ocean features, particularly during summer months in tropical regions.

In the past these upper ocean features have gone unseen by satellite-based temperature sensors because they are effectively camouflaged beneath a very shallow and stable layer of warmer water.

Tropical cyclone wind forces easily erode this thin upper layer by mixing the upper waters to depths that may go down to 100 meters, giving the tropical cyclones the potential to absorb ocean thermal energy, if conditions are appropriate. Now, estimates of TCHP based on satellite observations of sea surface temperature and sea surface height can detect these features.

Researcher Gustavo Goni, Joaquin Trinanes and Peter Black of the US National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory (NOAA/AOML) are working on this original methodology to detect these warm water masses and to compute their tropical cyclone heat potential values using several satellite sensors including one on Envisat.

“These water features are critical for identifying regions of high TCHP values that may potentially contribute to the intensification of a hurricane?, Goni explained. “These regions of high TCHP values provide the hurricanes with the opportunity to absorb much more thermal energy if overall conditions are right. My research is taking advantage of the fact that these warm water masses cause an upward elevation in ocean height of up to 30 cm. Such sea height anomalies can then be mapped with space-based radar altimeter data.”

Radar altimeters, such as the Radar Altimeter-2 instrument on Envisat, fire hundreds of radar pulses down to Earth every second, and by timing their return down the nanosecond can measure sea height to a maximum accuracy of two centimetres from hundreds of kilometres above the Earth.

The US Naval Research Laboratory (NRL) combines Envisat RA-2 data with data from similar radar altimeters aboard the Jason-1 and GFO satellites to enhance overall accuracy and spatial and temporal coverage, forming the source for altimetry products which, in turn, form the basis for NOAA/AOML-produced maps of tropical cyclone heat potential depicting the upper ocean thermal conditions, shown here overlaid against Hurricane Frances’ track so far.

“At this time I use this product only for research purposes, providing an enhanced understanding of the life of a hurricane. However, analogous products are being produced and used operationally for forecasting by the National Hurricane Center”, Goni concluded.

Altimetry-based wind speed and wave height products are also distributed by the French firm Collecte Localisation Satellites (CLS), and can reveal sea surface features related to the presence of hurricanes.

Envisat results to be revealed
Launched in March 2002, ESA’s Envisat satellite is an extremely powerful means of monitoring the state of our world and the impact of human activities upon it. Envisat carries ten sophisticated instruments to observe and monitor the Earth’s atmosphere, land, oceans and ice caps, maintaining continuity with the Agency’s ERS missions started in 1991.

After two and a half years in orbit, more than 700 scientists from 50 countries are about to meet at a special symposium in Salzburg in Austria to review and discuss early results from the satellites, and present their own research activities based on Envisat data.

Starting on Monday, the Envisat Symposium will address almost all fields of Earth science, including atmospheric chemistry, coastal studies, radar and interferometry, winds and waves, vegetation and agriculture, landslides, natural risks, air pollution, ocean colour, oil spills and ice.

There are over 650 papers being presented at the Symposium, selected by peer review. Presentations will include results on the Prestige oil spill, last year’s forest fires in Portugal, the Elbe flooding in 2002, the evolution of the Antarctic ozone hole, the Bam earthquake and pollution in Europe.

Numerous demonstrations are planned during the week in the ESA Exhibit area. An industrial consortium exhibit on the joint ESA-European Commission Global Monitoring for Environment and Security (GMES) initiative is also planned.

Original Source: ESA News Release

NASA is keeping a close watch over Hurricane Frances as it churns toward the United States. International Space Station cameras are capturing spectacular images of the storm from above. On the Florida coast, NASA’s Kennedy Space Center (KSC) is making preparations to protect the Space Shuttle fleet, spacecraft hardware, and facilities against damage.

Video of Hurricane Frances taken by external television cameras aboard the Space Station at about 7:30 a.m. EDT today vividly depicts a classically shaped storm in the Atlantic Ocean. The video, along with additional views captured during the weekend, is airing on the NASA TV Video File throughout the day. NASA will release new footage of Frances as it becomes available.

NASA also has still images of the storm, taken by Astronaut Mike Fincke aboard the International Space Station, as well as NASA’s Terra satellite. They’re available at:

http://www.nasa.gov/vision/earth/lookingatearth/frances.html

At KSC, workers are powering down the Space Shuttle orbiters, closing their payload bay doors and stowing their landing gear. They are also taking precautions against flooding by moving spacecraft hardware off the ground and sandbagging facilities. NASA plans to release video of these activities beginning tomorrow.

NASA TV is available on the Web and via satellite, in the continental U.S. on AMC-6, Transponder 9C, C-Band, located at 72 degrees west longitude. The frequency is 3880.0 MHz. Polarization is vertical, and audio is monaural at 6.80 MHz. In Alaska and Hawaii, NASA TV is available on AMC-7, Transponder 18C, C-Band, located at 137 degrees west longitude. Frequency is 4060.0 MHz. Polarization is vertical, and audio is monaural at 6.80 MHz.

Original Source: NASA News Release

For the first time, scientists may now detect a phytoplankton bloom in its early stages by looking at its red “glow” under sunlight, due to the unique data from two NASA satellites. According to a study conducted in the Gulf of Mexico, this phenomenon can forewarn fishermen and swimmers about developing cases of red tides that occur within plumes of dark-colored runoff from river and wetlands, sometimes causing “black water” events.

Dark-colored river runoff includes nitrogen and phosphorus, which are used as fertilizers in agriculture. These nutrients cause blooms of marine algae called phytoplankton. During extremely large phytoplankton blooms where the algae is so concentrated the water may appear black, some phytoplankton die, sink to the ocean bottom and are eaten by bacteria. The bacteria consume the algae and deplete oxygen from the water that leads to fish kills.

Chuanmin Hu and Frank Muller-Karger, oceanographers at the College of Marine Science of University of South Florida, St. Petersburg, Fla., used fluorescence data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard both NASA’s Terra and Aqua satellites. MODIS detects the glow or phytoplankton fluorescence, from the plant’s chlorophyll. The human eye cannot detect the red fluorescence.

The ability to detect glowing areas of water helps researchers identify whether phytoplankton are present in large dark water patches that form off the coast of Florida. Without these data, it is impossible to differentiate phytoplankton blooms from plumes of dark river runoff that contain few individual phytoplankton cells.

Because colored dissolved organic matter that originates in rivers can absorb similar amounts of blue and green color signals as plants do, traditional satellites that simply measure ocean color cannot distinguish phytoplankton blooms within such patches.

Although satellites cannot directly measure nutrients in lakes, rivers, wetlands and oceans, remote sensing technology measure the quantities of plankton. Scientists can then calculate how much nutrient might be needed to grow those amounts of plankton.

Hu and others used this technique to study the nature and origin of a dark plume event in the fall of 2003 near Charlotte Harbor, off the south Florida coast. Moderate concentrations of one of Florida’s red tide species, were found from water samples.

“Our study traces the black water patches near the Florida Keys to some 200 kilometers (124 miles) away upstream,” said Hu. “These results suggest that the delicate Florida Keys ecosystem is connected to what happens on land and in two remote rivers, the Peace and Caloosahatchee, as they drain into the ocean. Extreme climate conditions, such as abnormally high rainfall in spring and summer 2003, may accelerate such connections,” he added.

These findings are based on scientific analyses of several things. Data used include satellite ocean color from MODIS and Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and wind data from NASA’s QuikSCAT satellite. U.S. Geological Survey, National Oceanic and Atmospheric Administration (NOAA), Florida?s Fish and Wildlife Research Institute, and other organizations provided rain, river discharge, and field survey information.

By knowing which way the winds blow and the currents flow, Hu and colleagues can predict where black water may move.

Red tides occur every year off Florida and are known to cause fish kills, coral stress and mortality, and skin and respiratory problems in humans. Previous studies show that prolonged “black water” patches cause water quality degradation and may cause coral death. The use of remote sensing satellites provides effective means for monitoring and predicting such events.

The link between coastal runoff and black water events is an example of how land and ocean ecosystems are linked together. “Coastal and land managers over large areas need to work together, to alleviate more black water events from taking place in the future,” said Muller-Karger.

This study appeared in a recent issue of the American Geophysical Union’s Geophysical Research Letters. Coauthors of the article include Gabriel Vargo and Merrie Beth Neely from University of South Florida and Elizabeth Johns from NOAA’s Atlantic Oceanographic and Meteorological Laboratory.

NASA’s Science Directorate works to improve the lives of all humans through the exploration and study of Earth’s system, the solar system and the Universe.

Original Source: NASA News Release

A few NASA satellites designed to study heights of Earth’s ocean surfaces are now also coming in handy for tracking water levels of inland lakes and reservoirs.

When analysts at the United States Department of Agriculture (USDA) Foreign Agriculture Service (FAS) learned that NASA satellites could be used for measuring lake water heights, they saw a chance to get vital information for managing irrigation and forecasting crop production in out-of-the way places.

Since early this year, NASA has supplied the USDA with near-real time data on lake and reservoir heights from around the world. The USDA has posted this information on a web site that allows users with a computer and Internet to access it for their varied uses. Analysts who forecast crop production, scientists, in-country water and irrigation managers, those involved in fishing industries, and the general public have all been making use of the site.

NASA and the French space agency Le Centre National d?Etudes Spatiales (CNES) teamed up to design, build and launch the TOPEX/Poseidon and the Jason-1 satellites. These satellites were designed to study many aspects of the ocean. The TOPEX/Poseidon satellite, for example, orbits at a height of 1336 kilometers (830 miles) above Earth, and can measure the height of the ocean surface directly underneath the satellite with an accuracy of 4-5 centimeters (better than 2 inches). Jason-1 and TOPEX/Poseidon cover the global oceans every 10 days. With these capabilities, this technology is surprisingly valuable for looking at larger areas of inland water.

“The satellites were designed with oceanographic objectives in mind, so the fact that they can be used for lakes and rivers are an added bonus,” said Charon Birkett, a University of Maryland researcher based at NASA’s Goddard Space Flight Center in Greenbelt, Md. It was Birkett’s work with satellites and inland water sources that caught the USDA’s interest.

Water level data for many lakes can be hard to get. Lakes may be located within inhospitable regions. Terrain may make it hard to install water level gauges, or some countries may not have the money for proper equipment. Even if there is equipment, someone must be available to regularly record the measurements. For an international agency like the USDA FAS, information on water levels in remote lakes in Africa or Asia, for example, may only be possible if a researcher happens to be passing by the area.

“Now we have this dataset which gives you a global picture of irrigation capabilities,” said Brad Doorn, Remote Sensing Technical Coordinator for the FAS. “It’s very much a night and day perspective as it relates to global irrigation potential.”

NASA/CNES satellites fly over 350 of the world’s largest lakes. The USDA decided to focus on about 150 of those that are important for agriculture. Of those, about 70 are currently online, with more being regularly added as Birkett and co-worker, Brian Beckley, from Raytheon’s Information Technology and Scientific Services (ITSS) team learn to extract information on the smaller lakes. Fifteen of the lakes that are currently online are in Africa.

The records begin with archived data from TOPEX/Poseidon, launched in 1992. They continued with data from the Jason-1 satellite, launched in December 2001. The two stayed in the same orbit for about 7 months, before the TOPEX/Poseidon satellite’s orbit was changed. These months of cross-over data were crucial for validating each of the satellites and for making sure the data records from Jason-1 were compatible with the TOPEX/Poseidon archive.

The information provided by the satellites, and made public through the web site, is a blessing to those who manage water for irrigation. Irrigated areas generally have less rainfall, and therefore crops in these drier regions are dependent on stores of water, like lakes, reservoirs and rivers.

The FAS analyzes crop production around the world. They regularly use computer models that simulate agricultural production based on inputs that include weather information. In this way they can examine global crop conditions and production. But in irrigated areas that are not rain fed, these methods are limited. For irrigated areas, you have to be able to determine how much water is actually stored, after seasonal precipitation passes.

“Satellite records of lake and reservoir water levels give you a good indication of whether there is going to be a systematic or major problem in water supply,” said Doorn. “If water is low, there may be problems for agricultural production.” This type of information is especially important for food aid partners, who must budget ahead for how much and where food aid is distributed.

Lake Tharthar in Central Iraq provides irrigation water to areas downstream. It is also linked to the Tigris and Euphrates Rivers. A drought that carried over many years severely cut grain output between 1999 and 2001. But since then, rainfall has increased, allowing grain production to recover and even surpass pre-drought levels. Knowledge of water levels in a region like this is crucial for the people who divvy out water for irrigation, and for those who plan aid.

The satellites have noticed some striking changes in lake levels around the world. In Iran, Lake Urmia has steadily decreased over the last 5 years. Also, between 1999 and 2001, Lake Hamoun in Iran near the Afghanistan border all but dried up and disappeared. By May 2003, water had returned to the lake. In that same time period, Lake Michigan levels have also declined.

On the other hand, when there is plenty of water, irrigation managers and farmers can assess the potential for more agriculture. When Caspian Sea levels rose in 1994, spill-over created a reservoir where little water existed before. As a result, the Kara Bogaz reservoir that borders the Caspian Sea was once largely desert and is now a large inland water body. Lake Nasser in Egypt also exists in a desert area where water supplies have increased.

As can be seen, the new technology allows researchers to get water level records regularly, globally, and in places where it is very hard to maintain or even acquire measurements. At the same time, there are also some limitations to the technology. For example, lake elevations can only be obtained during the lifetime of the satellite mission. Also, a satellite must pass directly over a lake for the radar to record water heights. But since the primary mission of these satellites is for studying the oceans, the fixed satellite orbit is determined by the community of oceanographers. That means people studying inland water have less input into the lakes that are monitored. In addition, some water bodies are simply too small for the instruments to pick up. These factors limit the number of observable lakes. “Sometimes, the lake that you want information about is the one you can’t get,” said Doorn.

Despite the current limitations, users like the FAS are thrilled to have access to the technology. Their web site provides new measurements to the public about a week to ten days after the satellite passes over.

“When USDA approached us, we told them the satellite record is not as accurate as a gauge sitting in a lake, but we can get good information within one to two weeks for many lakes in data-poor regions such as Africa and Asia,” said Birkett.

“It’s been a great USDA and NASA cooperative effort,” said Doorn. “It’s exactly what we needed and the type of cooperation provided has made it a real win-win situation.”

The project has been a collaborative effort between the NASA GSFC, USDA FAS, the University of Maryland, and Raytheon ITSS. The project was funded by the USDA/FAS.

Original Source: NASA News Release

ESA?s quartet of space-weather watchers, Cluster, has discovered vortices of ejected solar material high above the Earth. The superheated gases trapped in these structures are probably tunnelling their way into the Earth?s magnetic ?bubble?, the magnetosphere. This discovery possibly solves a 17-year-mystery of how the magnetosphere is constantly topped up with electrified gases when it should be acting as a barrier.

The Earth?s magnetic field is our planet?s first line of defence against the bombardment of the solar wind. The solar wind itself is launched from the Sun and carries the Sun?s magnetic field throughout the Solar System. Sometimes this magnetic field is aligned with Earth?s and sometimes it points in the opposite direction.

When the two fields point in opposite directions, scientists understand how ?doors? in Earth?s field can open. This phenomenon, called ?magnetic reconnection?, allows the solar wind to flow in and collect in the reservoir known as the boundary layer. On the contrary, when the fields are aligned they should present an impenetrable barrier to the flow. However, spacecraft measurements of the boundary layer, dating back to 1987, present a puzzle because they clearly show that the boundary layer is fuller when the fields are aligned than when they are not. So how is the solar wind getting in?

Thanks to the data from the four formation-flying spacecraft of ESA?s Cluster mission, scientists have made a breakthrough. On 20 November 2001, the Cluster flotilla was heading around from behind Earth and had just arrived at the dusk side of the planet, where the solar wind slides past Earth?s magnetosphere. There it began to encounter gigantic vortices of gas at the magnetopause, the outer ?edge? of the magnetosphere.

?These vortices were really huge structures, about six Earth radii across,? says Hiroshi Hasegawa, Dartmouth College, New Hampshire who has been analysing the data with help from an international team of colleagues. Their results place the size of the vortices at almost 40 000 kilometres each, and this is the first time such structures have been detected.

These vortices are known as products of Kelvin-Helmholtz instabilities (KHI). They can occur when two adjacent flows are travelling with different speeds, so one is slipping past the other. Good examples of such instabilities are the waves whipped up by the wind slipping across the surface of the ocean. Although KHI-waves had been observed before, this is the first time that vortices are actually detected.

When a KHI-wave rolls up into a vortex, it becomes known as a ?Kelvin Cat?s eye?. The data collected by Cluster have shown density variations of the electrified gas, right at the magnetopause, precisely like those expected when travelling through a ?Kelvin Cat?s eye?.

Scientists had postulated that, if these structures were to form at the magnetopause, they might be able to pull large quantities of the solar wind inside the boundary layer as they collapse. Once the solar wind particles are carried into the inner part of the magnetosphere, they can be excited strongly, allowing them to smash into Earth?s atmosphere and give rise to the aurorae.

Cluster?s discovery strengthens this scenario but does not show the precise mechanism by which the gas is transported into Earth?s magnetic bubble. Thus, scientists still do not know whether this is the only process to fill up the boundary layer when the magnetic fields are aligned. For those measurements, Hasegawa says, scientists will have to wait for a future generation of magnetospheric satellites.

Original Source: ESA News Release

Originally developed to pinpoint attacking aircraft during World War Two, today’s advanced radar technology can detect a very different moving target: shifts of the Earth’s crust that occur as slowly as the growth of your fingernails.

Radar data from satellites such as ESA’s Envisat are used to construct ‘interferograms’ that show millimetre-scale land movements. These rainbow-hued images provide scientists with new insights into tectonic motion, and an enhanced ability to calculate hazards arising when this slow motion speeds up, in the form of earthquakes or volcanic activity.

The ten-instrument payload on Envisat includes an Advanced Synthetic Aperture Radar (ASAR) instrument designed to acquire radar images of the Earth’s surface. Part of Envisat’s assigned ‘background mission’ as it orbits the world every 100 minutes is to prioritise ASAR acquisitions over the seismic belts that cover 15% of the land surface.

“By the time Envisat completes its nominal five-year mission we should have a satisfactory amount of images across all the seismic belts,” said Professor Barry Parsons of the Centre for the Observation and Modelling of Earthquakes and Tectonics at Oxford University.

“To detect the fine ground deformation we are interested in, we require repeated radar images of each site. We then combine pairs of images together using a technique called SAR interferometry, or InSAR for short, to show up any change between acquisitions.” (For more information see link: How does interferometry work?)

To accurately measure the slow build up of strain as tectonic plates move against each other along Earth’s seismic belts, multiple interferograms are combined, requiring many individual SAR images.

“The reason for this is to minimise any atmospheric interference, relative to the small crustal deformation signal we are interested in,” added Parsons. “Using data from Envisat’s predecessor ERS, our group has recently measured tectonic movement across western Tibet with an accuracy of a few millimetres per year. The results show that slip rates across the major faults in the region are much smaller than had been previously thought and that the Tibetan plateau deforms like a fluid.”

InSAR can also be used to analyse much more abrupt ground motion: researchers have recently been employing Envisat data to chart ground deformation associated with the extremely active Piton de la Fournaise volcano on R?union Island in the Indian Ocean, and to identify the fault that caused Iran’s Bam earthquake in December 2003.

Finding fault after the Bam disaster
More than 26000 people were killed on 26 December 2003, when a 6.3 Richter scale earthquake devastated the Iranian oasis town of Bam. Its ancient citadel ? designated a World Heritage site ? collapsed into rubble. The Charter on Space and Major Disasters was activated so that spacecraft including Envisat acquired imagery to support international relief efforts.

Following Envisat’s background mission, a pre-earthquake image had been acquired of the Bam vicinity on 3 December 2003, and this was combined with a post-quake image acquired 7 January 2004 ? the earliest re-acquisition date possible due to Envisat’s 35-day global coverage ? to perform InSAR.

“This is the first time that Envisat data has been used to produce an interferogram following a major earthquake,” said Parsons, part of an international team studying the Bam quake including participants from the Geological Survey of Iran and the US Jet Propulsion Laboratory.

The results were surprising, establishing that while Bam lies in a seismic belt, this particular quake had come from a point no one had expected. Iran is like the filling in a geological sandwich as the Arabian plate advances into Eurasia, and so many seismic faults occur within its territory. Most notably, the Gowk fault located west of Bam has had several large quakes take place on it during the last two decades.

However the Envisat interferogram showed the Bam quake had resulted from the rupture of a previously undetected fault that extends under the southern part of town, its existence missed by ground surveys. The fault showed up as a distinct band of discontinuity in the interferogram, with motion either side of it ranging from around five up to as high as 30 centimetres.

As well as highlighting such surface changes, InSAR results can be used to indirectly peer beneath the ground, with software models calculating what geological occurrences fit the surface events. With Bam they found a slip exceeding two metres had taken place at a mean depth of 5.5 kilometres, along a distinct type of fault.

Coming around again
The more precisely a spacecraft’s position can be controlled, the smaller the InSAR image baseline – the spatial distance between initial and follow-up image acquisitions – and the better the quality of the final interferogram. During Envisat’s initial Bam revisit the baseline was large enough that ERS digital elevation data was needed to subtract topographic effects caused by a shifted view angle.

However for its subsequent revisit, 35 days later, the steering of the spacecraft was so precise that no topographic compensation was required, representing a formidable operational achievement for Envisat.

“Our Flight Dynamics team have computed an accuracy of 93 cm using precise orbit determination results from DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) and laser ranging observations,” stated Envisat Spacecraft Manager Andreas Rudolph.

“Special orbit manoeuvres were required to achieve this accuracy, along with hard work from teams at the European Space Operations Centre (ESOC) here in Germany and the European Space Research Institute (ESRIN) in Italy ? not to mention a bit of luck!”

Surveying an active volcano
Radar interferometry is used to study earthquakes as well as volcanoes – Envisat has been gathering data on one extremely lively example of the latter.

Standing 2631 metres above the Indian Ocean, the Piton de la Fournaise volcano is not situated along seismic belts or the associated ‘Ring of Fire’ but ? like Hawaii on the other side of the planet ? it is sited above a magma ‘hotspot’ in the Earth’s mantle.

The Institut de Physique du Globe de Paris (IPGP) operates an in-situ Volcano Observatory to monitor eruptions and associated activity.

“We have been observing this basaltic volcano for the last 25 years ? it is one of the most active volcanoes in the world,” commented Pierre Briole of IPGP. “In the last six years there have been 13 eruptions, with an average duration of one month. Between 1992 and 1998 was a quiet time, while eight eruptions occurred between 1984 and 1992.”

Deep subterranean processes drive surface volcanic activity ? lava fissures and eruptions occur because of lava channels or ‘dikes’ that extend up from high pressure magma chambers. Ground deformation either up or down in the vicinity of a volcano provides insights into what is taking place underground, but until recently the amount of ground points that could be measured was very limited.

“Back in the time of ground-based geodetic instruments it took several weeks to measure the coordinates of perhaps 20 points, to an accuracy of about one centimetre,” remembered Briole. “Then in the early 1990s came the Global Positioning System (GPS). Using GPS we could increase the number of points measured tenfold during a weeklong campaign, down to half-centimetre accuracy. But the ground deformation caused by an eruption is typically extremely localised in space, and these 200 points are spread out across the volcano’s area.”

It took another space-based technology to improve on GPS: interferograms of Piton de la Fournaise, based on more than 60 Envisat images acquired during the last year. IPGP is part of a team making use of the data that also includes participants from Blaise Pascal (Clermont-Ferrand II) and R?union Universities.

“We are lucky with Piton de la Fournaise, because its remote location in the middle of the ocean means there are no clashes with other potential Envisat targets, and so we get more acquisitions than most of the other users of ASAR imagery,” Briole added. “InSAR from Envisat has proved an extremely powerful tool for us, because it provides a very high density of information across the entire volcano.

“With new eruptions taking place so often our ground campaigns could not keep pace but interferometry gives us data on each eruption. And while the volcano is very difficult place to operate in ? often with poor visibility from the weather and a very steep eastern flank ? all parts of the volcano down to vegetation line are accessible with InSAR.”

InSAR reveals a pattern of ground inflation in the months preceding a new eruption, as pressure in the magma chamber increases. Following an eruption the pressure abates and deflation occurs.

Also revealed are localised deformations that occur as magma dikes propagate and reach the surface. The extent of the deformation associated with a new fissure indicates the depth at which it originates ? the wider the inflation, the deeper down the dike has come from.

InSAR volcanic monitoring was first established using ERS data, producing interferograms showing Italy’s highly-active Mount Etna appearing to ‘breathe’ between eruptions. And interferogram surveys of apparently extinct volcanoes along remote parts of the Andes have shown ground motion indicating some are in fact still active.

“There are plenty of interesting lines of enquiry using this technique, including the question of whether it is possible to predict when a volcano is going to erupt, and – with seismic faults often occurring near volcanoes – the question of whether seismic activity and volcanic eruptions are linked,” Briole added.

“For now our team are interested in characterising Piton de la Fournaise as accurately as we can, to perfect techniques we can later apply to volcanoes elsewhere and if possible to increase the number of acquisitions so as to demonstrate that InSAR monitoring of volcanoes has operational potential, providing early warning for civil protection authorities.”

Original Source: ESA News Release

NASA’s Terra satellite captured this true-color image of Hurricane Alex, the first Atlantic hurricane of the season, at noon EDT on Tuesday, August 3. Around that time, the Category 2 storm was pounding North Carolina’s Outer Banks with winds of up to 100 miles an hour. It’s expected to eventually turn east and head out to sea.

The resolution on this photo, from Terra’s Moderate Resolution Imaging Spectroradiometer (MODIS), is 2 kilometers per pixel.

Original Source: NASA News Release

Now more than 100 000 kilometres away from Earth, ESA’s Moon-bound spacecraft SMART-1 looked back at Earth and returned this planetary perspective of the Middle East and Mediterranean Sea.

‘Smart’ usage of the solar-electric propulsion system (the ion engine) has saved a lot of fuel and the spacecraft will get to the Moon earlier than expected.

Almost 20 kilograms of the xenon fuel could be saved out of the original 84 kilograms, which could then be used to get closer to the Moon than planned, to within distances of between 300 and 3000 kilometres. This will give a coverage of the lunar surface at higher resolution and sensitivity.

Original Source: ESA News Release

Once dismissed as a nautical myth, freakish ocean waves that rise as tall as ten-storey apartment blocks have been accepted as a leading cause of large ship sinkings. Results from ESA’s ERS satellites helped establish the widespread existence of these ‘rogue’ waves and are now being used to study their origins.

Severe weather has sunk more than 200 supertankers and container ships exceeding 200 metres in length during the last two decades. Rogue waves are believed to be the major cause in many such cases.

Mariners who survived similar encounters have had remarkable stories to tell. In February 1995 the cruiser liner Queen Elizabeth II met a 29-metre high rogue wave during a hurricane in the North Atlantic that Captain Ronald Warwick described as “a great wall of water? it looked as if we were going into the White Cliffs of Dover.”

And within the week between February and March 2001 two hardened tourist cruisers ? the Bremen and the Caledonian Star ? had their bridge windows smashed by 30-metre rogue waves in the South Atlantic, the former ship left drifting without navigation or propulsion for a period of two hours.

“The incidents occurred less than a thousand kilometres apart from each other,” said Wolfgang Rosenthal – Senior Scientist with the GKSS Forschungszentrum GmbH research centre, located in Geesthacht in Germany – who has studied rogue waves for years. “All the electronics were switched off on the Bremen as they drifted parallel to the waves, and until they were turned on again the crew were thinking it could have been their last day alive.

“The same phenomenon could have sunk many less lucky vessels: two large ships sink every week on average, but the cause is never studied to the same detail as an air crash. It simply gets put down to ‘bad weather’.”

Offshore platforms have also been struck: on 1 January 1995 the Draupner oil rig in the North Sea was hit by a wave whose height was measured by an onboard laser device at 26 metres, with the highest waves around it reaching 12 metres.

Objective radar evidence from this and other platforms ? radar data from the North Sea’s Goma oilfield recorded 466 rogue wave encounters in 12 years – helped convert previously sceptical scientists, whose statistics showed such large deviations from the surrounding sea state should occur only once every 10000 years.

The fact that rogue waves actually take place relatively frequently had major safety and economic implications, since current ships and offshore platforms are built to withstand maximum wave heights of only 15 metres.

In December 2000 the European Union initiated a scientific project called MaxWave to confirm the widespread occurrence of rogue waves, model how they occur and consider their implications for ship and offshore structure design criteria. And as part of MaxWave, data from ESA’s ERS radar satellites were first used to carry out a global rogue wave census.

“Without aerial coverage from radar sensors we had no chance of finding anything,” added Rosenthal, who headed the three-year MaxWave project. “All we had to go on was radar data collected from oil platforms. So we were interested in using ERS from the start.”

ESA’s twin spacecraft ERS-1 and 2 ? launched in July 1991 and April 1995 respectively ? both have a Synthetic Aperture Radar (SAR) as their main instrument.

The SAR works in several different modes; while over the ocean it works in wave mode, acquiring 10 by 5 km ‘imagettes’ of the sea surface every 200 km.

These small imagettes are then mathematically transformed into averaged-out breakdowns of wave energy and direction, called ocean-wave spectra. ESA makes these spectra publicly available; they are useful for weather centres to improve the accuracy of their sea forecast models.

“The raw imagettes are not made available, but with their resolution of ten metres we believed they contained a wealth of useful information by themselves,” said Rosenthal. “Ocean wave spectra provide mean sea state data but imagettes depict the individual wave heights including the extremes we were interested in.

“ESA provided us with three weeks’ worth of data ? around 30,000 separate imagettes ? selected around the time that the Bremen and Caledonian Star were struck. The images were processed and automatically searched for extreme waves at the German Aerospace Centre (DLR).”

Despite the relatively brief length of time the data covered, the MaxWave team identified more than ten individual giant waves around the globe above 25 metres in height.

“Having proved they existed, in higher numbers than anyone expected, the next step is to analyse if they can be forecasted,” Rosenthal added. “MaxWave formally concluded at the end of last year although two lines of work are carrying on from it ? one is to improve ship design by learning how ships are sunk, and the other is to examine more satellite data with a view to analysing if forecasting is possible.”

A new research project called WaveAtlas will use two years worth of ERS imagettes to create a worldwide atlas of rogue wave events and carry out statistical analyses. The Principal Investigator is Susanne Lehner, Associate Professor in the Division of Applied Marine Physics at the University of Miami, who also worked on MaxWave while at DLR, with Rosental a co-investigator on the project.

“Looking through the imagettes ends up feeling like flying, because you can follow the sea state along the track of the satellite,” Lehner said. “Other features like ice floes, oil slicks and ships are also visible on them, and so there’s interest in using them for additional fields of study.

“Only radar satellites can provide the truly global data sampling needed for statistical analysis of the oceans, because they can see through clouds and darkness, unlike their optical counterparts. In stormy weather, radar images are thus the only relevant information available.”

So far some patterns have already been found. Rogue waves are often associated with sites where ordinary waves encounter ocean currents and eddies. The strength of the current concentrates the wave energy, forming larger waves ? Lehner compares it to an optical lens, concentrating energy in a small area.

This is especially true in the case of the notoriously dangerous Agulhas current off the east coast of South Africa, but rogue wave associations are also found with other currents such as the Gulf Stream in the North Atlantic, interacting with waves coming down from the Labrador Sea.

However the data show rogue waves also occur well away from currents, often occurring in the vicinity of weather fronts and lows. Sustained winds from long-lived storms exceeding 12 hours may enlarge waves moving at an optimum speed in sync with the wind ? too quickly and they’d move ahead of the storm and dissipate, too slowly and they would fall behind.

“We know some of the reasons for the rogue waves, but we do not know them all,” Rosenthal concluded. The WaveAtlas project is scheduled to continue until the first quarter of 2005.

Original Source: ESA News Release

Aura, a mission dedicated to the health of the Earth’s atmosphere, successfully launched today at 6:01:59 a.m. EDT (3:01:59 a.m. PDT) from Vandenberg Air Force Base, Calif., aboard a Boeing Delta II rocket. Spacecraft separation occurred at 7:06 a.m. EDT (4:06 a.m. PDT), inserting Aura into a 438-mile (705-kilometer) orbit.

NASA’s latest Earth-observing satellite, Aura will help us understand and protect the air we breathe.

“This moment marks a tremendous achievement for the NASA family and our international partners. We look forward to the Aura satellite offering us historic insight into the tough issues of global air quality, ozone recovery and climate change,” said NASA Associate Administrator for Earth Science Dr. Ghassem Asrar. “This mission advances NASA’s exploration of Earth and will also better our understanding of our neighbors in the planetary system. Aura joins its siblings, Terra, Aqua and 10 more research satellites developed and launched by NASA during the past decade, to study our home planet,” he added.

Aura will help answer three key scientific questions: Is the Earth’s protective ozone layer recovering? What are the processes controlling air quality? How is the Earth’s climate changing? NASA expects early scientific data from Aura within 30-90 days.

Aura also will help scientists understand how the composition of the atmosphere affects and responds to Earth’s changing climate. The results from this mission will help scientists better understand the processes that connect local and global air quality.

Each of Aura’s four instruments is designed to survey different aspects of Earth’s atmosphere. Aura will survey the atmosphere from the troposphere, where mankind lives, through the stratosphere, where the ozone layer resides and protects life on Earth.

With the launch of Aura, the first series of NASA’s Earth Observing System satellites is complete. The other satellites are Terra, which monitors land, and Aqua, which observes Earth’s water cycle.

Aura’s four instruments are: the High Resolution Dynamics Limb Sounder (HIRDLS); the Microwave Limb Sounder (MLS); the Ozone Monitoring Instrument (OMI); and the Tropospheric Emission Spectrometer (TES). HIRDLS was built by the United Kingdom and the United States. OMI was built by the Netherlands and Finland in collaboration with NASA. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., constructed TES and MLS. NASA’s Goddard Space Flight Center, Greenbelt, Md., manages the Aura mission.

“Many people have worked very hard to reach this point and the entire team is very excited,” said Aura Project Manager Rick Pickering of Goddard.

NASA’s Earth Science Enterprise is dedicated to understanding the Earth as an integrated system and applying Earth System Science to improve prediction of climate, weather and natural hazards using the unique vantage point of space.

For Aura information and images on the Internet, visit:

http://www.gsfc.nasa.gov/topstory/2004/0517aura.html

and

http://www.nasa.gov/aura

Original Source: NASA News Release