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The satellite waiting to launch California Saturday aboard the last flight of the venerable Delta 2 rocket should allow scientists to more accurately track changes in the ice sheets of our planet using six green laser beams. a vital contribution to climate change research.
Researchers considering analyzing the new satellite's data say a better understanding of the Earth's ice will help them better understand the changing climate of our planet and predict how ice melting will help raise the level of sea.
NASA's $ 1 billion ICESat 2 mission is scheduled to take off at 5:46 am EDT (8:46 am EDT, 12:46 pm GMT) from Vandenberg Air Force Base, a military spaceport on the California central coast between Los Angeles and San Francisco.
The satellite will move into an orbit that flies from pole to pole aboard the last flight of the United Launch Alliance's Delta 2 rocket, a machinery launcher with 154 missions in its pedigree that is about to retire .
ICESat 2 stands for Ice, Cloud and Land Elevation Satellite 2, a sequel to NASA's ICESat mission that measured the global ice caps from 2003 to 2009. Equipped with a laser divided into six beams, ICESat 2 will fly around 500 kilometers ) over the planet in an orbit inclined at an angle of 92 degrees to the equator, giving the mission coverage of up to 88 degrees north and south latitude.
Featuring an enhanced laser instrument designed to provide more accurate measurements than its predecessor, ICESat 2 will extend a data series that has shown that ice was melting around the edges of Greenland and Antarctica and was found to be a major source of data. thinned in the oceans.
In recent years, NASA has continued to monitor ice heights through an airborne campaign called Operation Ice Bridge, showing that some of the melting trends detected by the ICESat satellite have continued after the end of 2009. But satellites like ICESat offer a more uniform coverage.
"What we have learned from ICES about the icecaps in Greenland and Antarctica is that they are losing ice around the coastal areas, which means they are losing ice and two, probably related to the ocean. Said Tom Wagner, a scientist with NASA's cryosphere program.
"With a plane, you can not do as many measurements as you can by satellite," said Wagner. "What we discovered with Ice Bridge is that the changes observed by ICESat are not only continuing, but they seem to be accelerating in some cases."
This is important because ice conditions are related to other factors that determine the Earth's climate, such as currents and temperatures in the oceans. And the rise in sea level could threaten cities along the coast.
"In Antarctica and Greenland, we have about two-thirds of the Earth's freshwater," said Helen Fricker, a member of the ICSat Scientific Definition Team at the Scripps Oceanographic Institution. "If all this ice melted, we would increase the global sea level by about 180 feet (54 feet) on average, which is very significant."
Altimetry data collected by the US and French satellite series TOPEX / Poseidon and Jason show that mean sea level increased by 77 millimeters (3 inches) from 1993 to 2017.
"ICESat 2 is truly a revolutionary new tool for sea ice and sea ice research," said Tom Neumann, ICESat 2 Project Assistant Researcher at NASA's Goddard Space Flight Center.
NASA has used satellites to survey the ice for decades, but it is easier to track the ice cover than to measure the height and to estimate the thickness of the ice and ice sheets covering Antarctica and the Antarctic. Greenland.
Rather than relying on a single laser beam, as ICES did, the new mission will launch six laser beams to the Earth and measure the time it takes for the light to bounce off the surface and return to a telescope aboard the ship. space.
"To measure or estimate the thickness of sea ice, ICESat 2 measures the altitude of sea ice floating in the ocean and compares it to the height of the water in the cracks of the ice," he said. Neumann. "By comparing these two elevations, we can calculate the height of the sea ice that gushes from the water of the ocean."
Only about one-tenth of the total sea ice exceeds the ocean's waterline. Scientists can therefore use the raw ICESat 2 measurements to determine the total thickness of floating ice in the sea. Scientists will then use ice height information in conjunction with spatial gravimetric measurements using the GRACE Follow-On mission, launched in May, to help scientists estimate the ice mass.
The ICESat 2 satellite was built by Northrop Grumman Innovation Systems and its unique instrument, the Advanced Laser Altimetry System (ATLAS), was developed at NASA's Goddard Space Flight Center.
"ATLAS essentially acts as a stopwatch," said Donya Douglas-Bradshaw, ATLAS Instrument Manager at Goddard. "The ATLAS laser fires 10,000 pulses per second with a trillion photons per shot. Whenever the laser goes off, it triggers the stopwatch. It takes about 3.3 milliseconds to beam out of the instrument, reach the surface and return to the telescope.
Only a dozen photons will reach the ICESat 2 receiver telescope, with the rest of the light diffusing into the atmosphere or space.
The laser package "has the ability to tag a single photon in a billionth of a second," Douglas-Bradshaw said in a briefing with reporters. "This accuracy allows the instrument to detect annual changes in ice elevation in the order of one-half inch (0.2 inch)."
The photon counting method is new and the development of the ATLAS laser has proven to be a challenge, delaying the launch of ICESat 2 by more than two years and adding hundreds of millions of dollars to the cost of the mission.
"The original ICESat mission was launched and the scientists looked at the data. They were very enthusiastic about it and they introduced themselves, and they said that this mission had to do a lot of things, "said Doug McLennan, Project Manager at ICESat 2 at Goddard. "It challenged the engineering team to design a mission capable of accomplishing these things. It was a very difficult mission to design the ATLAS instrument. It took longer than we thought, but now everything is buttoned and sitting on this rocket and ready to go.
The ATLAS ICESat 2 instrument actually comprises two lasers, a primary transmitter and a redundant transmitter, and the pulses pass through a diffractive optical element that divides the light into six green beams of 532 nanometers each, distributed over a band about 4 miles (6 kilometers) along the satellite ground track.
The lasers will travel from spacecraft to Earth in pairs, each separated by about 300 feet (90 meters) to provide measurements of the average slope of the ice. With 10,000 pulses per second on the 40 laser shots per second of the original ICESat mission, the ATLAS instrument will perform a height measurement along its trajectory every 2.3 feet (70 centimeters) when the satellite is travels at around 17,000 mph (27,000 kilometers per hour).
As ICESat 2 flies over the planet every hour and a half, the Earth will turn under the satellite's orbit, which will allow the mission to measure the height of the ice.
"We have an orbit that repeats itself exactly every 91 days," said McLennan. "It means we see the same piece of ice every three months. Each season, we measure what is happening on this ice and this allows us to accumulate a set of data from one year to another, from season to season. "
According to McLennan, the ICESat 2 satellite weighs about 1,515 kilograms at launch.
McLennan said the spacecraft has enough fuel to run for more than 10 years. The main mission of ICESat 2 is planned for three years, but could be extended.
Scientists working in other disciplines of Earth Sciences will also receive results from ICESat 2.
"ICESat 2 never goes out," said Lori Magruder, from the University of Texas at Austin, who led the team's scientific definition of the mission. "It works all the time, so you get measurements on every surface.
"We are getting measurements over the ocean and we are also measuring the interior water plans," she said. "It's important because we do not have global measurements that can tell us about our Earth's reservoirs, which certainly helps us to better understand our planet's water supply."
The laser telemetry instrument on ICESat 2 will also reveal new information on cloud structure when laser photons are returned to the satellite, and the mission should also provide estimates of forest heights.
"From the space point of view, we get an overall measure of tree height," said Magruder. "This allows us to create a global estimate of biomass. Biomass is important because it informs our knowledge of the carbon cycle and how it contributes to our environment and climate.
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Follow Stephen Clark on Twitter: @ StephenClark1.
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