With diminishing ice one of the greatest tolls on our warming world, it is essential to continue to make accurate measurements for scientific research and climate policy, as well as for practical applications such as ship steering.
To ensure the European Space Agency (ESA) and the United States Space Agency (NASA) get the best out of their ice-measuring satellites and to help prepare for Europe’s new CRISTAL satellite, the two space agencies, along with the British Antarctic Survey and a team of scientists recently teamed up to implement Plan an ambitious campaign in Antarctica.
The campaign involved taking simultaneous measurements of sea ice from the European Space Agency’s CryoSat and NASA’s ICESat-2 satellite, and from an aircraft flying directly below the two satellites.
It is the first time this has been done in Antarctica.
CryoSat carries a radar altimeter and ICESat-2 carries a laser. Both instruments measure the height of the ice by emitting a signal and timing the time it takes for the signal to bounce off the surface of the ice and return to the satellite.
Knowing the height of the ice allows scientists to calculate the thickness—which, along with measurements of the extent of ice coverage, is essential to understanding how ice volume has changed, whether ice on land or ice floating in the sea.
This is particularly difficult on sea ice because snow can build up on top of the ice.
Determining the thickness of sea ice involves measuring the “buoyancy” of ice floesProminent rise from the water. However, snow can push the raft lower into the water, masking the true thickness of the ice. Therefore a snow loading correction must be applied to the data.
The combination of measurements from the two satellites allows the scientists to correct for this snow loading effect.
While the CryoSat radar penetrates the snow layer and reflects closely from the ice below, the ICESat-2 laser reflects off the top of the snow layer. The simultaneous combination of satellite laser and radar means snow depth estimates will be more reliable.
However, the currents and winds shift the sea ice around. Under normal circumstances, the two satellites will take measurements at the same location days apart, so it could be different ice under their normal orbital tracks. Ice on Earth is, of course, less dynamic.
Until now, scientists haven’t been able to take full advantage of the simultaneous measurements recorded by each mission to monitor sea ice in the Southern Ocean.
Two years ago, the European Space Agency carried out the challenging task of raising the CryoSat’s orbital altitude by about 1 km to align its ground tracks with those of ICESat-2. This orbital adjustment provides a unique opportunity to compare simultaneous measurements from both satellite sensors.
Now that scientists have obtained two different types of measurements of the same sea ice, the recent Antarctic expedition was a key step in the inter-satellite calibration and paves the way for the future use of separate satellite measurement records.
For the campaign, the British Antarctic Survey’s DASH-7 aircraft is equipped with advanced sensors that simulate Radar altimeter on CryoSat and Laser on ICESat-2. It was also equipped with instruments that measured snow depth, surface albedo, and roughness.
The flights from the Rothera Research Station are timed to occur just like the orbiting satellites above, allowing the team to collect a set of high-resolution data about the sea ice itself. This will help the team develop more accurate algorithms to improve satellite-derived sea-ice thickness estimates.
By applying these algorithms to history Satellites A radar altimeter record such as CryoSat, will provide a time series of Antarctic sea ice thickness stretching back decades and fill gaps in knowledge of sea ice in the polar regions.
The DASH-7 aircraft also carried an additional set of sensors similar to those that will be carried on the Copernicus Ice and Snow Topography New Altimeter mission, or CRISTAL for short.
Instead of relying on radar and laser measurements from different satellites, the CRISTAL radar will use two different frequencies to measure and monitor the thickness of the sea ice, the depth of the ice above it, and the height of the ice sheet.
CRISTAL will ensure long-term continuity of glacial radar altimetry records and topographical change recordings, following CryoSat and other legacy missions.
This data will support safe marine operations in the polar oceans and contribute to a better understanding of climate processes. CRISTAL will also support applications related to coastal and inland waters, as well as provide observations of ocean topography.
“Flying DASH-7 is an exciting opportunity as it shows that we can bridge the gap that will arise between CryoSat and CRISTAL.”
ESA Research Fellow Isobel Lawrence noted, “The Antarctic campaign was essential in measuring future sea ice thickness from space.”
ESA’s CRISTAL mission scientist, Paolo Cipollini, added, “ESA is developing CRISTAL for the European Union’s Copernicus programme. This mission will provide critically needed long-term and continuous observations for polar climate monitoring, climate research and marine services. It is also expected enable an exciting new science, with its enhanced and expanded toolkit.”
European Space Agency
the quote: Future Proofing Ice Measurements from Space (2023, January 20) Retrieved January 20, 2023 from https://phys.org/news/2023-01-future-proofing-ice-space.html
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