ICESat-II, ELaNa-XVIII: ELFIN, IT-SPINS, CHEFsat - Delta II 7420-10C - Vandenberg SLC-2W -15.09.2018

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https://www.nasa.gov/feature/goddard/2018/operation-icebridge-icesat-2-join-forces-to-survey-antarctica
ЦитироватьOct. 12, 2018

Operation IceBridge, ICESat-2 Join Forces To Survey Antarctica

NASA's decade-long airborne survey of polar ice, Operation IceBridge, is once again probing Antarctica. But this year is different: it is the first time that the IceBridge team and instruments survey the frozen continent while NASA's newest satellite mission, the Ice, Cloud and land Elevation Satellite-2 (ICESat-2), studies it fr om space.

After successfully flying over the Bailey Ice Stream and Slessor Glacier in East Antarctica on Oct. 10, IceBridge will spend the next five weeks measuring changes in Antarctic sea and land ice while precisely flying under orbits of ICESat-2 to compare measurements.
Спойлер
IceBridge began flying in 2009 to maintain continuity of laser-altimetry measurements between NASA's ICESat missions. The original ICESat mission ended in 2009, and its successor, ICESat-2, was launched this past Sept. 15. Since then, ICESat-2 has successfully collected its first height measurements across the Antarctic Ice Sheet on Oct. 3.

"After a decade of flying both poles every year, we're finally bridging the two ICESat satellite missions," said Joe MacGregor, IceBridge's project scientist and a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It's hugely satisfying to be part of building this key observational record of change in the polar regions."


The Shackleton Range in Antarctica at sunset with snow blowing off the ridges, photographed during an Operation IceBridge flight on Oct. 10, 2018.
Credits: NASA/Michael Studinger

"This campaign is our second-to-last Antarctic campaign and it is arguably the most scientifically diverse that IceBridge has ever done," MacGregor said. "We're going to be revisiting classic IceBridge targets: flights along glacier flowlines that have been surveyed since 2002, long-term sea ice flights, and new targets across West Antarctica. More than two dozen of these mission designs are relevant to both IceBridge and ICESat-2."

IceBridge and ICESat-2 both use laser altimeters that fire pulses of light toward the ground and measure how long it takes for that light to bounce off the ice and return to the instruments' sensors. Scientists can then calculate the distance between the aircraft or the satellite and the ice surface, which gives them the ice height.

When IceBridge flies along a track over Antarctica that ICESat-2 has either just or is about to pass over as it orbits in space, pilots will align the plane so that the swath fired by IceBridge's laser altimeter encompasses the tracks of two of ICESat-2's six laser beams. Researchers will then look for overlap between the IceBridge and ICESat-2 returns and compare their measurements of ice height.


IceBridge's Airborne Topographic Mapper instrument, or ATM, has two lasers that shoot thousands of pulses of light per second in a circular motion that, combined with the plane's forward motion, result in spiral patterns of height measurements over Earth's surface. At the altitude that IceBridge typically conducts polar surveys, the lasers' swaths are 650 feet and 130 feet wide, respectively. Each single measurement, or laser pulse, for either instrument has a 3-foot footprint on the ground. In contrast, ICESat-2 takes measurements following six unique lines on the ground, one for each of its laser beams. The footprint of each ICESat-2 laser pulse is about 56 feet in diameter.
Credits: NASA/Kelly Brunt, Adriana Manrique

During this year's Antarctic campaign, the IceBridge team will fly under some of ICESat-2's orbits over sea and land ice. The underflights over sea ice to collect measurements of freeboard — the total height of the snow cover and sea ice that floats above the ocean — are particularly tricky. The ice that floats over the Southern Ocean is in constant motion, so in order to survey the same patches of sea ice that ICESat-2 will have flown over a few hours earlier or later that day, the IceBridge scientists will first have to figure out where that sea ice has drifted.


A coastal polynya, or opening in the sea ice cover, near the Filchner Ice Shelf in Antarctica, as seen during an Operation IceBridge flight on Oct. 10, 2018.
Credits: NASA/John Sonntag

"We're going to be chasing sea ice," said Linette Boisvert, IceBridge's deputy project scientist and a sea ice researcher at Goddard. "To do so, we will take the plane down to a lower altitude and remain there for a few seconds to measure wind speed and direction. We'll plug these data into a code that accounts for drift and other forces, calculating where the sea ice that ICESat-2 flew over is currently located. Then, we'll adjust our route to fly over it. On the way back to base, we'll drop lower again to measure wind speed, readjust our trajectory and chase sea ice again."

Another modification to meet ICESat-2's needs will be performing a sea ice survey at twilight. Normally, IceBridge only conducts its flights in broad daylight, but, since ICESat-2 will be taking measurements around the clock, the scientists want to check whether laser data are more accurate at low light, when there is less interference on the laser instrument's sensors from the Sun.

Over land ice, IceBridge will retrace some of ICESat-2's tracks over the ice sheet and its outlet glaciers, with a particular interest in areas of blue ice. Those are sections of the ice sheet wh ere the wind has scoured the snow off and exposed nearly pure ice. The intercomparison of measurements of blue ice, with no snow interference, will help ICESat-2 researchers understand how much the laser signal can penetrate ice.

While flying over Antarctica, IceBridge will also collaborate with satellite missions and international research groups as weather and time allow. During the sea ice surveys, the IceBridge plane may also fly under the tracks of ESA's (European Space Agency) CryoSat-2 and the European Union's Sentinel-3 satellites. During a survey flight over Thwaites Glacier, one of the fastest-changing glaciers in West Antarctica, IceBridge may collect seafloor measurements to support the International Thwaites Glacier Collaboration, a joint campaign between the United States and the United Kingdom.

This year, IceBridge flights to Antarctica will begin first from Punta Arenas, in southern Chile, and later from Ushuaia, in southern Argentina. The surveys will be conducted from NASA's DC-8 airborne science laboratory. The plane, managed by NASA's Armstrong Flight Research Center in Palmdale, California, carries IceBridge's full instrument suite.

IceBridge's main instrument is a dual-color laser altimeter from NASA's Wallops Flight Facility in Virginia that measures surface elevation by transmitting both infrared and green laser pulses. The airborne mission also uses two types of radar systems from the Center for Remote Sensing of Ice Sheets at the University of Kansas to study ice layers and Antarctica's bedrock. Wallops also contributes a high-resolution camera to collect color images of the ice surface and infrared cameras to read surface temperatures of sea and land ice. Goddard provides a hyperspectral imager to the mission that takes measurements over hundreds of wavelengths and Columbia University in New York manages a gravimeter to map the seafloor underneath the ice shelves.
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Last Updated: Oct. 12, 2018
Editor: Rob Garner

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https://www.nasa.gov/image-feature/icesat-2-reveals-profile-of-ice-sheets
ЦитироватьDec. 11, 2018

ICESat-2 Reveals Profile of Ice Sheets



Less than three months into its mission, NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, is already exceeding scientists' expectations. The satellite is measuring the height of sea ice to within an inch, tracing the terrain of previously unmapped Antarctic valleys, surveying remote ice sheets, and peering through forest canopies and shallow coastal waters.

With each pass of the ICESat-2 satellite, the mission is adding to datasets tracking Earth's rapidly changing ice. Researchers are ready to use the information to study sea level rise resulting from melting ice sheets and glaciers, and to improve sea ice and climate forecasts.

In this image, sea ice forms in the open water between floes, called leads, in the Bellingshausen Sea. ICESat-2 is able to detect the thin sea ice, allowing scientists to more accurately track seasonal ice formation.

Image Credit: NASA/Kate Ramsayer

Last Updated: Dec. 11, 2018
Editor: Yvette Smith

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ЦитироватьNew NASA Satellite Reveals Profiles of Ice, Forests and Oceans

NASA Goddard

Опубликовано: 11 дек. 2018 г.

Спойлер
Less than three months into its mission, NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, is already exceeding scientists' expectations. The satellite is measuring the height of sea ice to within an inch, tracing the terrain of previously unmapped Antarctic valleys, surveying remote ice sheets, and peering through forest canopies and shallow coastal waters.

With each pass of the ICESat-2 satellite, the mission is adding to datasets tracking Earth's rapidly changing ice. Researchers are ready to use the information to study sea level rise resulting from melting ice sheets and glaciers, and to improve sea ice and climate forecasts.
[свернуть]
https://www.youtube.com/watch?v=VTVXrnuvGzU
https://www.youtube.com/watch?v=VTVXrnuvGzU (1:02)

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https://www.nasa.gov/feature/goddard/2018/icesat-2-reveals-profile-of-ice-sheets-sea-ice-forests
ЦитироватьDec. 11, 2018

ICESat-2 Reveals Profile of Ice Sheets, Sea Ice, Forests

Less than three months into its mission, NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, is already exceeding scientists' expectations. The satellite is measuring the height of sea ice to within an inch, tracing the terrain of previously unmapped Antarctic valleys, surveying remote ice sheets, and peering through forest canopies and shallow coastal waters.

With each pass of the ICESat-2 satellite, the mission is adding to datasets tracking Earth's rapidly changing ice. Researchers are ready to use the information to study sea level rise resulting fr om melting ice sheets and glaciers, and to improve sea ice and climate forecasts.

"ICESat-2 is going to be a fantastic tool for research and discovery, both for cryospheric sciences and other disciplines," said Tom Neumann, ICESat-2 project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Neumann and others with ICESat-2's science team shared the first look at the satellite's findings at the American Geophysical Union's annual meeting on Tuesday in Washington, D.C.

Filling in the gaps

Спойлер
In topographic maps of Transantarctic Mountains, which divide East and West Antarctica, there are places where other satellites just can't see. Some instruments don't orbit that far south, others only pick up large features or the highest points and so miss minor peaks and valleys. With an early pass of ICESat-2, scientists started to fill in those details.

"It's spectacular terrain," said Benjamin Smith, a glaciologist with the University of Washington, Seattle, and member of the ICESat-2 science team. "We're able to measure slopes that are steeper than 45 degrees, and maybe even more, all through this mountain range."

As ICESat-2 orbits over the Antarctic Ice Sheet, the photon returns reflect fr om the surface and show high ice plateaus, crevasses in the ice 65 feet (20 meters) deep, and the sharp edges of ice shelves dropping into the ocean. These first measurements can help fill in the gaps of Antarctic maps, Smith said, but the key science of the ICESat-2 mission is yet to come. As researchers refine knowledge of where the instrument is pointing, they can start to measure the rise or fall of ice sheets and glaciers.

"Very soon, we'll have measurements that we can compare to older measurements of surface elevation," Smith said. "And after the satellite's been up for a year, we'll start to be able to watch the ice sheets change over the seasons."
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On thin ice

Спойлер
When sea ice first forms on polar oceans, before snow falls on it and wind smashes it into other floes, it is thin, flat and smooth. Which makes it a good place to test out how precise ICESat-2 data is, since long stretches should all be nearly the same height, said Ron Kwok, a sea ice scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. 
 

As ICESat-2 orbited over Antarctica, it took height measurements over the steep Queen Maud Mountains - some of which had never been previously measured. Over the Ross Ice Shelf, the photon return data showed a mostly flat surface, broken by terrain including the Crary Ice Rise.
Credits: NASA Earth Observatory/Joshua Stevens

So far? "The data's spectacular," Kwok said. "The fresh ice is totally flat to within a couple centimeters."

The first months of ICESat-2 data collected over Arctic and Antarctic sea ice reveal thin ice, thick ice, and features such as ice ridges. Areas of open water in the cracks between the ice floes, called leads, stand out in the data because of the difference in reflectivity between ice and water. By comparing the height of that water surface in the leads with the height of the ice, scientists are estimating ice freeboard and thickness. With the high precision of ICESat-2, plus the satellite's six beams taking data simultaneously, researchers will have an unprecedented understanding of the thickness of sea ice, which will be used to help improve climate modeling and forecasts.

Plus, the ability to identify newly formed, thin ice will help researchers track the seasonal changes in remote polar regions, and understand the processes that drive those processes. The ice-thickness data will also help scientists improve computer models of how sea ice responds to Arctic warming, as well as forecasts of sea ice cover.

"We'll have much higher resolution of where it's ice and where it's water in the marginal ice zones, wh ere the compact ice cover meets the ocean, during melt and freeze-up," Kwok said. "That's going to be new science to think about. "
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Beyond ice

Спойлер
ICESat-2 is always on, taking measurements not only at the poles but also in the tropical and temperate latitudes, and what it can see has already surprised researchers.


Sea ice of different thickness and bumpiness is broken up by the cracks between floes, called leads, in this graph of photon returns from ICESat-2 as it orbits over the Weddell Sea in Antarctica.
Credits: NASA Earth Observatory/Joshua Stevens

"We were all taken aback seeing the amazing detail from ICESat-2, thanks to its detection technology," said Lori Magruder, a research scientist at the University of Texas and the ICESat-2 science team lead. "On every surface, there was some amazing feature that we weren't used to seeing with the first ICESat."

For example, photons returning from over the ocean trace individual waves. In clear coastal areas, the bathymetry is visible, sometimes as deep as 80 feet (25 meters), which could help with research including storm surge modeling, Magruder said. 

And as ICESat-2 orbits over forests, it can distinguish not only the tops of trees but also the inner canopies and the forest floor. While the team was unsure how clear the terrain would be under dense canopies like those found in tropical rainforests, the data turned out even better than expected. By measuring tree heights globally, the ICESat-2 mission will be able to improve estimates of how much carbon is stored in forests.
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Checking the numbers, bridging the gap

Спойлер
As the ICESat-2 science team was analyzing the first sets of data, colleagues with NASA's Operation IceBridge were collecting data in aircraft over Antarctica – flying over the same paths that the satellite was orbiting.


ICESat-2 is on all the time - and so takes height measurements over land, forests and oceans as well as ice. As it orbited over Mexico, the satellite measurements who the height of trees as well as the forest floor, plus the bathymetry of a lagoon and the ocean waves beyond.
Credits: NASA Earth Observatory/Joshua Stevens

Over vast plains of rippling ice, craggy peaks poking through the ice sheet, and lines of crevasses marching down glaciers, the airborne campaign measured surface elevation with the Airborne Topographic Mapper's laser altimeters, snow and ice thickness with radars, and sub-ice-shelf bathymetry with a gravimeter. For a decade, IceBridge has been surveying the region, but this fall they were also gathering data to help check the accuracy of ICESat-2.

In three separate flights, IceBridge surveyed the flat plateau along the 88-degree-south latitude line wh ere all ICESat-2 orbits converge. Other flights tracked across glaciers, ice streams and mountains along individual satellite paths – at times right as the satellite passed overhead. To measure sea ice, the IceBridge team flew briefly at 500 feet to measure wind speed, calculated how far the ice had moved since ICESat-2 measured it, and then adjusted the flight path to survey the same patch of ice.

"Almost every flight has ICESat-2 tracks incorporated into it," said Joseph MacGregor, IceBridge project scientist at NASA Goddard. "We fly over fast-changing outlet glaciers, the slower-changing interior, and uncommon surfaces that are interesting to ICESat-2. The primary goal for IceBridge is to bridge the gap between ICESat and ICESat-2, so it's very rewarding to know that we're completing that process."

The first ICESat satellite operated between 2003 and 2009, which is when IceBridge began its campaigns. ICESat-2 launched on Sept. 15 from Vandenberg Air Force Base in California. Its laser instrument, called ATLAS (Advanced Topographic Laser Altimeter System), sends pulses of light to Earth. It then times, to within a billionth of a second, how long it takes individual photons to return to the satellite. ATLAS has fired its laser more than 50 billion times since first turning on Sept. 30, and all the metrics from the instrument show it is working as it should, Neumann said.
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Mission managers expect to release the data to the public in early 2019.

Credits: Kate Ramsayer

By Kate Ramsayer
NASA's Goddard Space Flight Center, Greenbelt, Md. 

Last Updated: Dec. 13, 2018
Editor: Sara Blumberg

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ЦитироватьMeasuring Sea Ice Thickness With ICESat-2

NASA Video

14 мая 2020 г.

A view of the Arctic Ocean with monthly average sea ice thickness spanning November 2018 to March 2019. Low values are depicted in light blue, and higher values (5 meters) are depicted in magenta.
https://www.youtube.com/watch?v=o4HZvvVEyCEhttps://www.youtube.com/embed/o4HZvvVEyCE (0:27)

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https://www.nasa.gov/feature/goddard/2020/icesat-2-measures-arctic-sea-ice-thickness-snow-cover
ЦитироватьMay 14, 2020

NASA's ICESat-2 Measures Arctic Ocean's Sea Ice Thickness, Snow Cover

Arctic sea ice helps keep Earth cool, as its bright surface reflects the Sun's energy back into space. Each year scientists use multiple satellites and data sets to track how much of the Arctic Ocean is covered in sea ice, but its thickness is harder to gauge. Initial results from NASA's new Ice Cloud and land Elevation Satellite-2 (ICESat-2) suggest that the sea ice has thinned by as much as 20% since the end of the first ICESat mission (2003-2009), contrary to existing studies that find sea ice thickness has remained relatively constant in the last decade.

ICESat-2 has a laser altimeter, which uses pulses of light to precisely measure height down to about an inch. Each second, the instrument sends out 10,000 pulses of light that bounce off the surface of Earth and return to the satellite and records the length of time it takes to make that round trip. The light reflects off the first substance it hits, whether that's open water, bare sea ice or snow that has accumulated on top of the ice, so scientists use a combination of ICESat-2 measurements and other data to calculate sea ice thickness.

By comparing ICESat-2 data with measurements from another satellite, researchers have also created the first satellite-based maps of the amount of snow that has accumulated on top of Arctic sea ice, tracking this insulating material.

"The Arctic sea ice pack has changed dramatically since monitoring from satellites began more than four decades ago," said Nathan Kurtz, ICESat-2 deputy project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The extraordinary accuracy and year-round measurement capability of ICESat-2 provides an exciting new tool to allow us to better understand the mechanisms leading to these changes, and what this means for the future."


Scientists have used NASA's ICESat-2 to measure the thickness of Arctic sea ice, as well as the depth of snow on the ice. Here, ridges and cracks have formed in sea ice in the Arctic Ocean.
Credits: NASA / Jeremy Harbeck

Arctic sea ice thickness dropped drastically in the first decade of the 21st Century, as measured by the first ICESat mission from 2003 to 2009 and other methods. The European Space Agency's CryoSat-2, launched in 2010, has measured a relatively consistent thickness in Arctic sea ice since then. With the launch of ICESat-2 in 2018, researchers looked to this new way of measuring sea ice thickness to advance the study of this data record.

"We can't get thickness just from ICESat-2 itself, but we can use other data to derive the measurement," said Petty. For example, the researchers subtract out the height of snow on top of the sea ice by using computer models that estimate snowfall. "The first results were very encouraging."

In their study, published recently in the Journal of Geophysical Research: Oceans, Petty and his colleagues generated maps of Arctic sea ice thickness from October 2018 to April 2019 and saw the ice thickening through the winter as expected.

Overall, however, calculations using ICESat-2 found that the ice was thinner during that time period than what researchers have found using CryoSat-2 data. Petty's group also found that small but significant 20% decline in sea ice thickness by comparing February/March 2019 ICESat-2 measurements with those calculated using ICESat in February/March 2008 – a decline that the CryoSat-2 researchers don't see in their data.

These are two very different approaches to measuring sea ice, Petty said, each with its own limitations and benefits. CryoSat-2 carries a radar to measure height, as opposed to ICESat-2's lidar, and radar mostly passes through snow to measure the top of the ice. Radar measurements like the ones from CryoSat-2 could be thrown off by seawater flooding the ice, he noted. In addition, ICESat-2 is still a young mission and the computer algorithms are still being refined, he said, which could ultimately change the thickness findings.

"I think we're going to learn a lot from having these two approaches to measuring ice thickness. They might be giving us an upper and lower bound on the sea ice thickness, and the right answer is probably somewhere in between," Petty said. "There are reasons why ICESat-2 estimates could be low, and reasons why CryoSat-2 could be high, and we need to do more work to understand and bring these measurements in line with each other."

With ICESat-2 and CryoSat-2 using two different methods to measure ice thickness – one measuring the top of the snow, the other the boundary between the bottom of the snow layer and the top of the ice layer – but researchers realized they could combine the two to calculate the snow depth.

"This is the first time ever that we can get snow depth across the entire Arctic Ocean's sea ice cover," said Ron Kwok, a sea ice scientist at NASA's Jet Propulsion Laboratory in Southern California and author of another study in JGR Oceans. "The Arctic region is a desert – but what snow we do get is very important in terms of the climate and insulating sea ice."

The study found that snow starts building up slowly in October, when newly formed ice has an average of about 2 inches (5 centimeters) of snow on it and multiyear ice has an average of 5.5 inches (14 cm) of snow. Snowfall picks up later in the winter in December and January and reaches its maximum depth in April, when the relatively new ice has an average of 6.7 inches (17 cm) and the older ice has an average of 10.6 inches (27 cm) of snow.

When the snow melts in the spring, it can pool up on the sea ice – those melt ponds absorb heat from the Sun and can warm up the ice faster, just one of the impacts of snow on ice.

By Kate Ramsayer

NASA's Goddard Space Flight Center, Greenbelt, Maryland


Last Updated: May 14, 2020
Editor: Kate Ramsayer