Le vol du Corbeau ou Nicosie
|yanis la chouette|
Nombre de messages : 5016
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005
|Sujet: Re: Le vol du Corbeau ou Nicosie Lun 13 Fév à 8:46|| |
Projet Ariel ou Uranus I sur la connaissance de déplacement
NASA, UCI Reveal New Details of Greenland Ice Loss
› NASA's OMG is the first campaign ever to map all of the glaciers and ocean around Greenland's coastline.
› NASA researchers have learned from OMG's first year that cold water from the melting glaciers is cooling warmer subsurface ocean water, with possible implications for how much ocean heat reaches Greenland's glaciers.
› A UC Irvine-led research team has applied the data to improve coastline maps used to predict future rates of sea level rise.
Less than a year after the first research flight kicked off NASA's Oceans Melting Greenland campaign last March, data from the new program are providing a dramatic increase in knowledge of how Greenland's ice sheet is melting from below. Two new research papers in the journal Oceanography use OMG observations to document how meltwater and ocean currents are interacting along Greenland's west coast and to improve seafloor maps used to predict future melting and subsequent sea level rise.
The five-year OMG campaign studies the glaciers and ocean along Greenland's 27,000-mile coastline. Its goal is to find out where and how fast seawater is melting the glacial ice. Most of the coastline and seafloor around the ice sheet had never been surveyed, so the 2016 flights alone expanded scientists' knowledge of Greenland significantly. Future years of data collection will reveal the rate of change around the island.
The water circulating close around the Greenland Ice Sheet is like a cold river floating atop a warm, salty ocean. The top 600 feet (200 meters) of colder water is relatively fresh and comes from the Arctic. Below that is saltwater from the south, 6 to 8 degrees Fahrenheit (3 to 4 degrees Celsius) warmer than the fresher water above. The layers don't mix much because freshwater weighs less than saltwater, so it stays afloat.
If a glacier reaches the ocean where the seafloor is shallow, the ice interacts with frigid freshwater and melts slowly. Conversely, if the seafloor in front of a glacier is deep, the ice spills into the warm subsurface layer of saltwater and may melt relatively rapidly. Satellite remote sensing can't see below the surface to discern the depth of the seafloor or study the layers of water. OMG makes these measurements with shipboard and airborne instruments.
Tracking meltwater far into the North
In one of the two new papers, Ian Fenty of NASA's Jet Propulsion Laboratory, Pasadena, California, and coauthors tracked water up the west coast to see how how it changed as it interacted with hundreds of melting coastal glaciers. They found that in northwest Greenland, cold and fresh water flowing into glacial fjords from the melting surface of the ice sheet is cooling the warmer subsurface water, which circulates clockwise around the island. In one instance, evidence for meltwater-cooled waters was found in fjords 100 miles (160 kilometers) downstream from its source. Fenty noted, "This is the first time we've documented glacier meltwater significantly impacting ocean temperatures so far downstream. That shows meltwater can play an important role in determining how much ocean heat ultimately reaches Greenland's glaciers."
The OMG data have enough detail that researchers are beginning to pinpoint the ice-loss risk for individual glaciers along the coast, according to OMG Principal Investigator Josh Willis of JPL. "Without OMG, we wouldn't be able to conclude that Upernavik Glacier is vulnerable to ocean warming, whereas Cornell Glacier is less vulnerable," he said.
Improving maps used to project sea level rise
In the second paper, lead author Mathieu Morlighem of the University of California, Irvine, used the OMG surveys to refine and improve maps of the bedrock under some of the west coast glaciers. Glaciologists worldwide use these and other maps in modeling the rate of ice loss in Greenland and projecting future losses.
A coastal glacier's response to a warming climate depends heavily not only on the depth of the seafloor in front of it, as explained above, but on the shape of the bedrock below it. Before OMG, virtually the only measurements Morlighem had of these critical landscapes were long, narrow strips of data collected along flight lines of research aircraft, sometimes tens of miles inland (upstream) from a glacier's ocean front. He has been estimating the shape of the bedrock outside of the flight lines with the help of other data such as ice flow speeds, but has had no good way to check how accurate his estimates are at the coastline.
Morlighem noted, "OMG [data are] not only improving our knowledge of the ocean floor, they're improving our knowledge of the topography of the land, too." This is because the campaign's seafloor survey revealed features under the ocean, such as troughs cut by glaciers during the last ice age, that must continue upstream under the glacial ice. Therefore, Morlighem said, "By having OMG's measurements close to the ice front, I can tell whether what I thought about the bed topography is correct or not." Morlighem was pleasantly surprised to discover that 90 percent of the glacier depths he had estimated were within 160 feet (50 meters) of the actual depths recorded by the OMG survey.
The two papers are available online:
Oceans Melting Greenland: Early Results from NASA's Ocean-Ice Mission in Greenland:
Improving bed topography mapping of Greenland glaciers using NASA's Oceans Melting Greenland (OMG) data...
|yanis la chouette|
Nombre de messages : 5016
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005
|Sujet: Re: Le vol du Corbeau ou Nicosie Lun 13 Fév à 8:50|| |
One Role of Mars Orbiter: Check Possible Landing Sites
› NASA's Mars Reconnaissance Orbiter has provided about 300 terabits of data about Mars, more than all other interplanetary missions combined.
› Those data yield the mission's own science findings, plus crucial information for evaluating possible Mars landing sites for future missions.
› A workshop this week is using the mission's data to narrow the list of possible sites for NASA's next Mars rover.
At an international workshop this week about where NASA's next Mars rover should land, most of the information comes from a prolific spacecraft that's been orbiting Mars since 2006.
Observations by NASA's Mars Reconnaissance Orbiter (MRO) provide the basis for evaluating eight candidate landing sites for the Mars 2020 rover mission. The landing site workshop this week in Monrovia, California, will narrow the Mars 2020 candidate list to four or fewer sites. MRO observations have been used to identify, characterize and certify past landing sites and are also in use to assess possible sites for future human-crew missions.
"From the point of view of evaluating potential landing sites, the Mars Reconnaissance Orbiter is the perfect spacecraft for getting all the information needed," said the workshop's co-chair, Matt Golombek of NASA's Jet Propulsion Laboratory, Pasadena, California. "You just can't overstate the importance of MRO for landing-site selection."
Engineers use MRO data to evaluate the safety of a candidate landing site. For example, stereoscopic 3-D information can reveal whether slopes are too steep, and some detailed images can show individual boulders big enough to be a landing hazard. Scientists use MRO data to evaluate how well a site could serve the research goals of a mission, such as the distribution of minerals that may have originated in wet environments.
"Missions on the surface of Mars give you the close-up view, but what you see depends on where you land. MRO searches the globe for the best sites," said MRO Deputy Project Scientist Leslie Tamppari of JPL.
Images, terrain models and mineral maps from the orbiter help the teams that operate NASA's two active Mars rovers plan driving routes. The Mars 2020 team has already used MRO data to evaluate driving options in the eight candidate sites for that rover, which is on track for launch in the summer of 2020 and landing in early 2021. The site evaluations even use MRO's capability to study the atmosphere above each site and probe underground features with ground-penetrating radar.
In the progress toward selecting a landing site for a future human mission to Mars, NASA is using MRO data to evaluate about 45 suggested sites that could support human exploration zones, which are areas that could support astronauts as they explore up to a 60-mile radius.
Still, the hundreds of MRO observations targeted specifically for study of potential landing sites make up a small fraction of all the data the mission has provided about Mars. MRO has acquired more than 224,000 images and millions of other observations during its nearly 50,000 orbits around Mars. This month, the mission will reach and pass a milestone of 300 terabits of total science data sent to Earth from the orbiter. That tops the combined total from all other interplanetary missions, past and present. It is more data than would be included in four months of nonstop high-definition video.
"Whether it is looking at the surface, the subsurface or the atmosphere of the planet, MRO has viewed Mars from orbit with unprecedented spatial resolution, and that produces huge volumes of data," said MRO Project Scientist Rich Zurek of JPL."These data are a treasure trove for the whole Mars scientific community to study as we seek to answer a broad range of questions about the evolving habitability, geology and climate of Mars."
One of the orbiter's six instruments has provided images of 99 percent of Mars -- equivalent to 97 percent of Earth's land area -- in resolution sufficient to show features smaller than a tennis court. One-fifth of this coverage area has been imaged at least twice, providing stereo, 3-D information. Another instrument has returned several multi-spectral data sets for mapping surface composition, including one covering nearly 85 percent of Mars.The highest-resolution camera onboard has returned images revealing details as small as a desk in swaths covering a carefully chosen 2.8 percent of Mars's surface. That's more than the areas of Texas, California, and all the states east of the Mississippi River combined.
Other instruments on MRO have provided daily weather maps of the entire planet since 2006, more than 20,000 radar-observing strips to examine subsurface layers of ice and rock, and more than 8.8 million atmospheric profiles of temperatures, clouds and dust.
New discoveries flow from the copious MRO data. Some are:
Minerals mapped by MRO indicate a diversity of ancient water-related environments, many apparently habitable.
There is enough carbon-dioxide ice buried in the south polar cap that, if released, it could more than double the planet's present atmosphere.
Mars is a dynamic planet today, with dust storms, moving sand dunes, avalanches, new gullies and fresh impact craters.
Reservoirs of buried water ice that are remnants of past climates, including buried glaciers, have been confirmed and discovered.
Dark flows that appear in warm seasons on some slopes suggest brine activity, though they are still enigmatic and hold scant water at most.
Mars' north polar cap is geologically young -- about five million years old -- and contains unequally spaced layers of dust and ice that are apparently related to cyclical changes in the planet's tilt.
Large dust storms during southern spring and summer appear to have a pattern of three types, in sequence.
Seasonal surface changes at mid to high latitudes appear related to freezing and thawing of carbon dioxide.
In addition to MRO's observations, whether for landing-site assessment or direct science investigations, the orbiter also provides communication relay service for robots on the Martian surface, whether mobile or stationary. This month, MRO will reach and pass a milestone of 6,000 relay sessions for Mars-surface missions.
For additional information about MRO, visit: