Hola amigos: A VUELO DE UN QUINDE EL BLOG., la Administración Nacional de Aeronáutica y del Espacio - NASA en español; nos informa sobre un estudio de la Misión: Operación IceBridge, que al sobrevolar la península antártica del norte, que sucedió el 16 de octubre del 2018, vieron un iceberg rectangular de ángulo muy afilado que flotaba entre el hielo marino justo al lado de la plataforma de hielo Larsen C...
La Misión IceBridge de la NASA Fotografía un Curioso Iceberg Rectangular
24.10.18.- La misión Operación IceBridge, el estudio aéreo más largo de la NASA sobre el hielo polar, sobrevoló la península antártica del norte el 16 de Octubre de 2018. Durante el estudio, diseñado para evaluar los cambios en la altura del hielo de varios glaciares que desembocan en Larsen A, B y C Embayments, el científico de apoyo de IceBridge, Jeremy Harbeck, vio un iceberg rectangular de ángulo muy afilado que flotaba entre el hielo marino justo al lado de la plataforma de hielo Larsen C. Una foto del iceberg fue ampliamente compartida después de que fue publicada en las redes sociales.
"Creí que era muy interesante; a menudo veo icebergs con bordes relativamente rectos, pero realmente no he visto uno antes con dos esquinas en ángulos rectos como este", dijo Harbeck. El iceberg rectangular parecía haberse separado de Larsen C, que en Julio de 2017 lanzó el masivo iceberg A68, un trozo de hielo del tamaño del estado de Delaware, EE.UU.
Harbeck capturó tanto el borde del ahora famoso iceberg como un iceberg un poco menos rectangular. Esa imagen también capta a A68 en la distancia.
"En realidad, estaba más interesado en capturar el iceberg A68 sobre el que estábamos a punto de sobrevolar, pero pensé que este iceberg rectangular era visualmente interesante y bastante fotogénico, por lo que, al menos, tomé un par de fotos", dijo Harbeck.
El vuelo se originó en Punta Arenas, Chile, como parte de un despliegue de IceBridge de cinco semanas de duración, que comenzó el 10 de Octubre y está programado para concluir el 18 de Noviembre.
Image Credit: NASA/Jeremy Harbeck
Oct. 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 from 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.
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/John Sonntag
“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 where 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.
For more information on IceBridge, and to follow the 2018 Antarctic flights, visit:
Banner image: An icefall along the edge of Bailey Ice Stream in East Antarctica, as seen during an Operation IceBridge flight on Oct. 10, 2018. Credit: NASA/Jeremy Harbeck
Last Updated: Oct. 15, 2018
Editor: Rob Garner
La Pérdida de Glaciares en la Antártida Occidental Parece Imparable
14.05.14.- Un nuevo estudio realizado por investigadores de la NASA y la Universidad de California, Irvine, ha detectado una sección de la Antártida Occidental en rápido deshielo que parece haber alcanzado ya un estado irreversible de decadencia, sin nada que impida que los glaciares en esta área acaben derritiéndose en el mar.
El estudio presenta varias líneas de evidencia, con 40 años de observaciones que indican que los glaciares en el sector del Mar de Amundsen de la Antártida occidental "han pasado el punto de no retorno", según el glaciólogo y autor principal Eric Rignot, de la Universidad de California Irvine y el Laboratorio de Propulsión a Chorro de la NASA en California.
Estos glaciares ya contribuyen de manera significativa al aumento del nivel del mar, liberando casi la misma cantidad de hielo en el océano anualmente que toda la capa de hielo de Groenlandia. Contienen suficiente hielo para elevar el nivel global del mar en 1,2 metros y se están derritiendo más rápido de lo que la mayoría de los científicos esperaban. Rignot dijo que estos hallazgos requieren una revisión al alza de las previsiones actuales de la subida del nivel del mar. "Este sector será uno de los que más contribuya al aumento del nivel del mar durante las próximas décadas y siglos", dijo Rignot. "Una estimación conservadora es que podría llevar varios siglos que todo el hielo desemboque en el mar".
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| El glaciar Thwaites. Image Credit: NASA |
Tres grandes líneas de evidencia apuntan a la eventual desaparición de los glaciares: los cambios en las velocidades de flujo, la cantidad de cada glaciar que flota en el agua de mar y la pendiente del terreno que está fluyendo y su profundidad bajo el nivel del mar. En un artículo en abril, el grupo de investigación de Rignot discutió las velocidades de flujo cada vez mayores de estos glaciares en los últimos 40 años. Este nuevo estudio analiza las otras dos líneas de evidencias.
Los glaciares fluyen hacia fuera, de la tierra hacia el mar, con sus bordes de ataque a flote en el agua de mar. El punto en un glaciar que primero pierde el contacto con la tierra se llama línea de conexión a tierra. Casi todo el deshielo de los glaciares se produce en la parte inferior del glaciar más allá de la línea de conexión a tierra, en la sección flotante de agua de mar.
Así como un barco encallado puede flotar de nuevo en agua poco profunda si se vuelve más ligero, un glaciar puede flotar sobre una zona donde solía estar conectado a tierra si se vuelve más ligero, lo que puede ocurrir por fusión o por los efectos de adelgazamiento de los glaciares que se extienden hacia fuera. Los glaciares de la Antártida estudiados por el grupo de Rignot han adelgazado tanto que ahora están flotando por encima de los lugares donde solían asentarse firmemente en la tierra, lo que significa que sus líneas de conexión a tierra se están retirando hacia el interior.
“La línea de conexión a tierra está enterrada bajo más de mil metros de hielo, por lo que es muy difícil para un observador humano en la superficie de la lámina de hielo averiguar exactamente donde está la transición”, dijo Rignot. “Este análisis se realiza mejor usando técnicas de satélite.”
El equipo utilizó observaciones de radar captadas entre 1992 y 2011 por los satélites europeos ERS-1 y 2 para trazar la retirada tierra adentro de las líneas de conexión a tierra. Los satélites utilizan una técnica llamada interferometría de radar, lo que permite a los científicos medir de manera muy precisa el movimiento. También utilizaron datos de espesor de hielo de la misión Operación IceBridge de la NASA.
Los resultados confirman que no hay puntos de fijación aguas arriba de las actuales líneas de conexión a tierra en cinco de los seis glaciares. Sólo el glaciar Haynes tiene importantes obstáculos corriente arriba, pero afecta a un sector pequeño y está retrocediendo tan rápidamente como los otros glaciares. “El colapso de este sector de la Antártida occidental parece ser imparable. El hecho de que la retirada esté sucediendo al mismo tiempo en un sector grande sugiere que fue provocado por una causa común, como el aumento en la cantidad de calor del océano que hay por debajo de las secciones flotantes de los glaciares. En este punto, parece que el final de este sector es inevitable”, concluye Rignot.
NASA
NASA
Massive Iceberg Breaks Off from Antarctica
Thermal wavelength image of a large iceberg, which has calved off the Larsen C ice shelf. Darker colors are colder, and brighter colors are warmer, so the rift between the iceberg and the ice shelf appears as a thin line of slightly warmer area. Image from July 12, 2017, from the MODIS instrument on NASA's Aqua satellite.
Credits: NASA Worldview
An iceberg about the size of the state of Delaware split off from Antarctica’s Larsen C ice shelf sometime between July 10 and July 12. The calving of the massive new iceberg was captured by the Moderate Resolution Imaging Spectroradiometer on NASA’s Aqua satellite, and confirmed by the Visible Infrared Imaging Radiometer Suite instrument on the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite. The final breakage was first reported by Project Midas, an Antarctic research project based in the United Kingdom.
Animation of the growth of the crack in the Larsen C ice shelf, from 2006 to 2017, as recorded by NASA/USGS Landsat satellites.
Credits: NASA/USGS Landsat
Larsen C, a floating platform of glacial ice on the east side of the Antarctic Peninsula, is the fourth largest ice shelf ringing Earth’s southernmost continent. In 2014, a crack that had been slowly growing into the ice shelf for decades suddenly started to spread northwards, creating the nascent iceberg. Now that the close to 2,240 square-mile (5,800 square kilometers) chunk of ice has broken away, the Larsen C shelf area has shrunk by approximately 10 percent.
Throughout the sunlit months of late 2016 and early 2017, scientists watched closely as a crack grew across the Larsen C ice shelf on the Antarctic Peninsula. On June 17, 2017, the Thermal Infrared Sensor (TIRS) on Landsat 8 captured a false-color image of the crack and the surrounding ice shelf. It shows the relative warmth or coolness of the landscape. Orange depicts where the surface is the warmest, most notably the areas of open ocean and of water topped by thin sea ice. Light blues and whites are the coldest areas, spanning most of the ice shelf and some areas of sea ice. Dark blue and purple areas are in the mid-range.
Credits: NASA's Earth Observatory
The blue hue of the crack indicates that relatively warm ocean water is not far below the ice surface. No part of the crack appears as warm as ocean areas, likely because there is a soup of floating, broken ice pieces from the rift’s walls and bits of sea ice sitting atop the water-filled crack. (This mixture can act as a weak glue, but it also prevents the rift from healing.)
Credits: NASA's Earth Observatory
“The interesting thing is what happens next, how the remaining ice shelf responds,” said Kelly Brunt, a glaciologist with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland in College Park. “Will the ice shelf weaken? Or possibly collapse, like its neighbors Larsen A and B? Will the glaciers behind the ice shelf accelerate and have a direct contribution to sea level rise? Or is this just a normal calving event?”
Ice shelves fringe 75 percent of the Antarctic ice sheet. One way to assess the health of ice sheets is to look at their balance: when an ice sheet is in balance, the ice gained through snowfall equals the ice lost through melting and iceberg calving. Even relatively large calving events, where tabular ice chunks the size of Manhattan or bigger calve from the seaward front of the shelf, can be considered normal if the ice sheet is in overall balance. But sometimes ice sheets destabilize, either through the loss of a particularly big iceberg or through disintegration of an ice shelf, such as that of the Larsen A Ice Shelf in 1995 and the Larsen B Ice Shelf in 2002. When floating ice shelves disintegrate, they reduce the resistance to glacial flow and thus allow the grounded glaciers they were buttressing to significantly dump more ice into the ocean, raising sea levels.
Scientists have monitored the progression of the rift throughout the last year was using data from the European Space Agency Sentinel-1 satellites and thermal imagery from NASA’s Landsat 8 spacecraft. Over the next months and years, researchers will monitor the response of Larsen C, and the glaciers that flow into it, through the use of satellite imagery, airborne surveys, automated geophysical instruments and associated field work.
In the case of this rift, scientists were worried about the possible loss of a pinning point that helped keep Larsen C stable. In a shallow part of the sea floor underneath the ice shelf, a bedrock protrusion, named the Bawden Ice Rise, has served as an anchor point for the floating shelf for many decades. Ultimately, the rift stopped short of separating from the protrusion.
“The remaining 90 percent of the ice shelf continues to be held in place by two pinning points: the Bawden Ice Rise to the north of the rift and the Gipps Ice Rise to the south,” said Chris Shuman, a glaciologist with Goddard and the University of Maryland at Baltimore County. “So I just don’t see any near-term signs that this calving event is going to lead to the collapse of the Larsen C ice shelf. But we will be watching closely for signs of further changes across the area.”
The first available images of Larsen C are airborne photographs from the 1960s and an image from a US satellite captured in 1963. The rift that has produced the new iceberg was already identifiable in those pictures, along with a dozen other fractures. The crack remained dormant for decades, stuck in a section of the ice shelf called a suture zone, an area where glaciers flowing into the ice shelf come together. Suture zones are complex and more heterogeneous than the rest of the ice shelf, containing ice with different properties and mechanical strengths, and therefore play an important role in controlling the rate at which rifts grow. In 2014, however, this particular crack started to rapidly grow and traverse the suture zones, leaving scientists perplexed.
“We don’t currently know what changed in 2014 that allowed this rift to push through the suture zone and propagate into the main body of the ice shelf,” said Dan McGrath, a glaciologist at Colorado State University who has been studying the Larsen C ice shelf since 2008.
McGrath said the growth of the crack, given our current understanding, is not directly linked to climate change.
“The Antarctic Peninsula has been one of the fastest warming places on the planet throughout the latter half of the 20th century. This warming has driven really profound environmental changes, including the collapse of Larsen A and B,” McGrath said. “But with the rift on Larsen C, we haven’t made a direct connection with the warming climate. Still, there are definitely mechanisms by which this rift could be linked to climate change, most notably through warmer ocean waters eating away at the base of the shelf.”
While the crack was growing, scientists had a hard time predicting when the nascent iceberg would break away. It’s difficult because there are not enough measurements available on either the forces acting on the rift or the composition of the ice shelf. Further, other poorly observed external factors, such as temperatures, winds, waves and ocean currents, might play an important role in rift growth. Still, this event has provided an important opportunity for researchers to study how ice shelves fracture, with important implications for other ice shelves.
The U.S. National Ice Center will monitor the trajectory of the new iceberg, which is likely to be named A-68. The currents around Antarctica generally dictate the path that the icebergs follow. In this case, the new berg is likely to follow a similar path to the icebergs produced by the collapse of Larsen B: north along the coast of the Peninsula, then northeast into the South Atlantic.
“It’s very unlikely it will cause any trouble for navigation,” Brunt said.
By Maria-Jose Viñas
NASA’s Earth Science News Team
Additional media contact: Rani Gran, NASA's Goddard Space Flight Center, Greenbelt, Md.
Last Updated: Aug. 6, 2017
Editor: Rob Garner
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