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Author Topic: ICESat-2 data now available  (Read 2504 times)

AndyW

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ICESat-2 data now available
« on: September 01, 2019, 08:17:29 PM »
« Last Edit: July 30, 2020, 04:06:14 AM by oren »

slow wing

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Re: Icesat 2 data now available
« Reply #1 on: September 01, 2019, 10:37:01 PM »
Excellent news, thanks!  :)

ArcticMelt2

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Re: Icesat 2 data now available
« Reply #2 on: December 14, 2019, 06:21:13 AM »
First mission results

https://twitter.com/AGU_Cryo/status/1205668130359365632



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There’s been a thinning of about 40cm in Arctic #seaice since ICESat-1 (10 years) 📉 #AGU19


ArcticMelt2

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Re: Icesat 2 data now available
« Reply #3 on: December 14, 2019, 06:30:04 AM »

ArcticMelt2

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Re: Icesat 2 data now available
« Reply #4 on: December 14, 2019, 10:19:07 AM »


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For small melt ponds, hard to get a depth measurement, you still find them though! Because they saturate the signal



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.@NASA_ICESat2 is also doing an awesome job finding (big) melt ponds, including their depth!


ArcticMelt2

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Re: Icesat 2 data now available
« Reply #5 on: December 14, 2019, 10:20:57 AM »
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Heavy snowfall in Antarctica can make it difficult to determine freeboard bc you have to determine how deep the radar is penetrating



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They’re showing different things for #seaice floe lengths, maybe because they are detecting refrozen leads in different ways


ArcticMelt2

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Re: Icesat 2 data now available
« Reply #6 on: May 15, 2020, 10:09:01 AM »
https://www.nasa.gov/feature/goddard/2020/icesat-2-measures-arctic-sea-ice-thickness-snow-cover
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JC015764

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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.

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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.

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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.

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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.

ArcticMelt2

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Re: Icesat 2 data now available
« Reply #7 on: May 15, 2020, 10:14:53 AM »
A very important study. It means that CryoSat-2 shows much more ice in the Arctic than it actually is.

Radars are a bad thing to measure the thickness of ice. Do not see the snow. Lasers are good. They can work both in winter and summer. The only problem is cloudiness, but I think there are clear days in the Arctic every week.

Jim Hunt

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Re: Icesat 2 data now available
« Reply #8 on: May 15, 2020, 05:10:45 PM »
From the Petty et al. abstract:

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Sea ice thickness is calculated by combining the measured ICESat‐2 freeboards—the extension of sea ice above sea level—with a new snow on sea ice model.

It seems there's no way of getting away from modelling!
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

ArcticMelt2

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Re: Icesat 2 data now available
« Reply #9 on: May 15, 2020, 05:30:37 PM »
It is still unclear why satellite radars do not work in the Arctic in the summer, but can work to measure mean sea level.

For example:

https://en.wikipedia.org/wiki/Jason-3

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Jason-3 will make precise measurements related to global sea surface height. Because sea surface height is measured via altimetry, mesoscale ocean features are better simulated since the Jason-3 radar altimeter can measure global sea-level variations with very high accuracy.[5][6] The scientific goal is to produce global sea surface height measurements every 10 days to an accuracy of less than 4 cm.[7] In order to calibrate the radar altimeter, a microwave radiometer measures signal delay caused by atmospheric vapors, ultimately correcting the altimeter's accuracy to 3.3 cm.[5][8]


Different frequencies?

gerontocrat

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Re: Icesat 2 data now available
« Reply #10 on: May 15, 2020, 05:47:22 PM »
It is still unclear why satellite radars do not work in the Arctic in the summer, but can work to measure mean sea level.
Different frequencies?
[/quote]
I thought it was melt ponds
"Para a Causa do Povo a Luta Continua!"
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ArcticMelt2

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Re: Icesat 2 data now available
« Reply #11 on: May 15, 2020, 05:52:09 PM »
It is still unclear why satellite radars do not work in the Arctic in the summer, but can work to measure mean sea level.
Different frequencies?
I thought it was melt ponds


Are these melting ponds the same liquid water as the surface of the ocean? Why can not you accept the reflection from this liquid water? Or is the reason different salinity of the water?

ArcticMelt2

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Re: Icesat 2 data now available
« Reply #12 on: May 15, 2020, 06:13:22 PM »
Or is the reason different salinity of the water?

But this is the wrong reason. Radar satellites can measure the level of fresh lakes.

For example, Lake Superior in North America.

https://ipad.fas.usda.gov/cropexplorer/global_reservoir/

oren

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Re: ICESat-2 data now available
« Reply #13 on: July 30, 2020, 04:06:38 AM »
Discuss ICESAT-2 here.

oren

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Re: ICESat-2 data now available
« Reply #14 on: July 30, 2020, 04:14:49 AM »
https://www.nasa.gov/feature/goddard/2020/syncing-nasa-laser-esa-radar-for-a-new-look-at-sea-ice

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Syncing NASA Laser, ESA Radar for a New Look at Sea Ice
With a small nudge to a satellite’s orbit, scientists will soon have simultaneous laser and radar measurements of ice, providing new insights into Earth’s frozen regions. On July 16, the European Space Agency (ESA) begins a series of precise maneuvers that will push the orbit of its radar-carrying CryoSat-2 satellite about half a mile higher – putting it in sync with NASA’s laser-carrying Ice, Cloud and land Elevation Satellite 2, or ICESat-2.

When the maneuvers are complete later this summer, the two satellites will pass over a swath of the Arctic within a few hours of each other. That synchronous stretch, of more than 2,000 miles (3,200 kilometers) every day or so, will be key for studying sea ice, which floats on the Arctic Ocean and is moved around with currents and winds. If the satellites take measurements at different times, the two could be measuring different floes of fast-moving ice. Syncing up the satellites provides scientists with two datasets for the same ice.

“Combining these two measurements from space will lead to a golden age,” said Tommaso Parrinello, CryoSat-2 mission manager with ESA. “It’s a small change for CryoSat-2, but will be a revolution for the science.”

Both CryoSat-2’s radar and ICESat-2’s laser instrument, called a lidar, measure height by sending out signals and timing how long they take to reflect off Earth’s surface and return to their respective satellites. But the different signals bounce off some surfaces differently – including snow-covered sea ice. Radars like Cryosat-2’s will penetrate through the snow layer and reflect off the ice below. Laser instruments like ICESat-2’s will reflect off the top of the snow layer. The difference between the two will give scientists the depth of the snow atop sea ice.

“If you have laser and radar together, it gives you this really exciting opportunity to measure the depth of the snow, which we’ve really never been able to do before from space,” said Rachel Tilling, a sea ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland and the University of Maryland in College Park. “And with snow depth, we can get significantly more accurate measurements of sea ice thickness.”

With better measurements of snow depth and sea ice thickness, researchers can gain insights into the complex Arctic climate system. Sea ice might just be 10 feet thick or so, but it has an outsized effect on Earth’s climate, forming a kind of a protective blanket on the Arctic Ocean, Tilling said. The snow on top reflects radiation from the Sun, keeping the ice from melting and the ocean from warming. The ice itself acts as a barrier between the atmosphere and the ocean – removing it could alter circulation patterns that reach the more temperate parts of the globe. The new information could improve climate models, as well as lead to more accurate shipping navigation forecasts, she said.

The idea of aligning the two satellites has been floating around among the ice science community since CryoSat-2 launched in 2010, when ICESat-2 was still in the development stage, said Tom Neumann, ICESat-2 project scientist at NASA Goddard.

“This opens up new science possibilities that weren’t possible with either mission independently, especially for sea ice science,” Neumann said. “It’s a grassroots effort, promoted by the scientists and engineers asking if there was a way we can make this happen.”

The CryoSat-2 flight operations team took a look and after months of analyzing orbital dynamics came up with a plan. The European satellite orbits much higher and slower than the American one, so they couldn’t simply follow each other in tandem, said Ignacio Clerigo, CryoSat-2’s spacecraft operations manager. Instead, they realized they could raise the altitude of the spacecraft by just more than half a mile (900 meters), through a series of 15 precisely timed thruster burns, and then the two satellites would overlap every 19th orbit of CryoSat-2 and 20th orbit of ICESat-2. The overlaps are mostly over the Arctic; next Northern Hemisphere summer ESA might precisely alter the orbit again with another set of maneuvers to focus on the Antarctic during that region’s winter.

“It’s a challenge, not because of the maneuvers themselves, but because of the tight schedule,” Clerigo said. “We have continuous activities for two weeks. Each step depends on the previous one and if something does not go as expected, we will need to replan quickly to reach the target orbit.”