Andrew Yee
November 7th 05, 02:06 PM
ESA News
http://www.esa.int
7 November 2005
Envisat shows behemoth B-15A iceberg breaking up
After five years of being the world's largest free-floating object, the
B-15A iceberg has finally broken up off Antarctica's Cape Adare.
ESA's Envisat satellite's Advanced Synthetic Aperture Radar (ASAR) is
sensitive to ice, and has been tracking the movement of the drifting ice
object since the beginning of this year. Its latest imagery reveals the
bottle-shaped iceberg split into nine knife-shaped icebergs and a myriad
of smaller pieces on 27-28 October, the largest being formed by fractures
along the long axis of the original single iceberg.
Measuring -- until last week -- around 115 kilometres in length with an
area exceeding 2500 square kilometres, the iceberg had apparently run
aground off Cape Adare, the northernmost corner of the Victoria Land
Coast. This stranding appears to have led to flexing and straining which
resulted in the break-up.
"The long knife-shaped pieces suggest the iceberg has split along existing
lines of weakness within the iceberg," says Mark Drinkwater of ESA's Ocean
and Ice Unit. "These would have been pre-existing crevasses in the ice
shelf."
These new icebergs, named by the US National Oceanic and Atmospheric
Administration (NOAA) National Ice Center, will retain their parent's
title: the three largest island-sized pieces have been called B-15M, B-15N
and B-15P.
B-15A was the largest remaining section of the even larger B-15 iceberg
that calved from the nearby Ross Ice Shelf in March 2000 before breaking
up into smaller sections.
Since then its B-15A section drifted into McMurdo Sound, where its
presence blocked ocean currents and led to a build-up of sea ice that
decimated local penguin colonies, deprived of open waters for feeding.
During the spring of this year prevailing currents took B-15A slowly past
the Drygalski ice tongue. A full-fledged collision failed to take place,
but a glancing blow broke the end off Drygalski in mid-April.
The iceberg sailed on to have a less-destructive close encounter with the
Aviator Glacier ice tongue at Lady Newnes Bay before becoming stranded off
Cape Adare in mid-October.
Radar monitoring of Antarctic ice
ASAR is extremely useful for tracking changes in polar ice. ASAR can peer
through the thickest polar clouds and work through local day and night.
And because it measures surface texture, the instrument is also extremely
sensitive to different types of ice -- so the radar image clearly
delineates the older, rougher surface of icebergs from surrounding sea
ice, while optical sensors simply show a continuity of snow-covered ice.
Envisat's ASAR instrument monitors Antarctica in two different modes:
Global Monitoring Mode (GMM) provides 400-kilometre swath one-kilometre
resolution images, enabling rapid mosaicking of the whole of Antarctica to
monitor changes in sea ice extent, ice shelves and iceberg movement.
Wide Swath Mode (WSM) possesses the same swath but with 150-metre
resolution for a detailed view of areas of particular interest.
ASAR GMM images are routinely provided to a variety of users including the
National Ice Center, responsible for tracking icebergs worldwide.
Related news
* New collision looks imminent for B-15A iceberg
http://www.esa.int/esaCP/SEM0V56TI8E_index_0.html
* B-15A collides with Antarctic ice tongue
http://www.esa.int/esaCP/SEMEGLW797E_index_0.html
* Giant iceberg B-15A edges past floating ice pier
http://www.esa.int/esaEO/SEMQ5FRMD6E_index_0.html
* B-15A iceberg's close encounter monitored by Envisat
http://www.esa.int/esaEO/SEMIWT71Y3E_index_0.html
Related missions
* Envisat overview
http://www.esa.int/esaEO/SEMWYN2VQUD_index_0_m.html
In depth
* Earthwatching: B-15A
http://earth.esa.int/ew/special_events/iceberg-b15_antartic/sp_iceberg-b15.htm
Related links
* US National Ice Center
http://www.natice.noaa.gov/
IMAGE CAPTIONS:
[Image 1:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html]
The break-up of B-15A in progress off Cape Adare on 30 October 2005, as
seen Envisat's ASAR in Wide Swath Mode.
Credits: ESA
[Image 2:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html#subhead1]
Individual pieces of B-15A moving northward by currents from Cape Adare, 3
November, seen in this Envisat ASAR Global Monitoring Mode image. The
knife-shaped iceberg towards the bottom of the image is B-15K, a separate
iceberg from the original B-15 iceberg which is unconnected to the recent
B-15A break-up.
Credits: ESA
[Image 3:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html#subhead2]
The 27-28 October break-up of B-15A occurred off Cape Adare, the
northernmost extent of Queen Victoria Land, close to the former base of
Cape Hallett. The original B-15 calved from the Ross Ice Shelf to the
south, facing the Ross Sea, back in May 2000.
[Image 4:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html#subhead3]
B-15A still appeared intact in this Envisat ASAR image acquired 27 October
in Global Monitoring Mode.
Credits: ESA
[Image 5:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html#subhead4]
The break-up of B-15A has started in this Envisat ASAR image acquired 28
October in Global Monitoring Mode. The splits are likely to have occurred
along existing lines of weakness in the stranded iceberg.
Credits: ESA
http://www.esa.int
7 November 2005
Envisat shows behemoth B-15A iceberg breaking up
After five years of being the world's largest free-floating object, the
B-15A iceberg has finally broken up off Antarctica's Cape Adare.
ESA's Envisat satellite's Advanced Synthetic Aperture Radar (ASAR) is
sensitive to ice, and has been tracking the movement of the drifting ice
object since the beginning of this year. Its latest imagery reveals the
bottle-shaped iceberg split into nine knife-shaped icebergs and a myriad
of smaller pieces on 27-28 October, the largest being formed by fractures
along the long axis of the original single iceberg.
Measuring -- until last week -- around 115 kilometres in length with an
area exceeding 2500 square kilometres, the iceberg had apparently run
aground off Cape Adare, the northernmost corner of the Victoria Land
Coast. This stranding appears to have led to flexing and straining which
resulted in the break-up.
"The long knife-shaped pieces suggest the iceberg has split along existing
lines of weakness within the iceberg," says Mark Drinkwater of ESA's Ocean
and Ice Unit. "These would have been pre-existing crevasses in the ice
shelf."
These new icebergs, named by the US National Oceanic and Atmospheric
Administration (NOAA) National Ice Center, will retain their parent's
title: the three largest island-sized pieces have been called B-15M, B-15N
and B-15P.
B-15A was the largest remaining section of the even larger B-15 iceberg
that calved from the nearby Ross Ice Shelf in March 2000 before breaking
up into smaller sections.
Since then its B-15A section drifted into McMurdo Sound, where its
presence blocked ocean currents and led to a build-up of sea ice that
decimated local penguin colonies, deprived of open waters for feeding.
During the spring of this year prevailing currents took B-15A slowly past
the Drygalski ice tongue. A full-fledged collision failed to take place,
but a glancing blow broke the end off Drygalski in mid-April.
The iceberg sailed on to have a less-destructive close encounter with the
Aviator Glacier ice tongue at Lady Newnes Bay before becoming stranded off
Cape Adare in mid-October.
Radar monitoring of Antarctic ice
ASAR is extremely useful for tracking changes in polar ice. ASAR can peer
through the thickest polar clouds and work through local day and night.
And because it measures surface texture, the instrument is also extremely
sensitive to different types of ice -- so the radar image clearly
delineates the older, rougher surface of icebergs from surrounding sea
ice, while optical sensors simply show a continuity of snow-covered ice.
Envisat's ASAR instrument monitors Antarctica in two different modes:
Global Monitoring Mode (GMM) provides 400-kilometre swath one-kilometre
resolution images, enabling rapid mosaicking of the whole of Antarctica to
monitor changes in sea ice extent, ice shelves and iceberg movement.
Wide Swath Mode (WSM) possesses the same swath but with 150-metre
resolution for a detailed view of areas of particular interest.
ASAR GMM images are routinely provided to a variety of users including the
National Ice Center, responsible for tracking icebergs worldwide.
Related news
* New collision looks imminent for B-15A iceberg
http://www.esa.int/esaCP/SEM0V56TI8E_index_0.html
* B-15A collides with Antarctic ice tongue
http://www.esa.int/esaCP/SEMEGLW797E_index_0.html
* Giant iceberg B-15A edges past floating ice pier
http://www.esa.int/esaEO/SEMQ5FRMD6E_index_0.html
* B-15A iceberg's close encounter monitored by Envisat
http://www.esa.int/esaEO/SEMIWT71Y3E_index_0.html
Related missions
* Envisat overview
http://www.esa.int/esaEO/SEMWYN2VQUD_index_0_m.html
In depth
* Earthwatching: B-15A
http://earth.esa.int/ew/special_events/iceberg-b15_antartic/sp_iceberg-b15.htm
Related links
* US National Ice Center
http://www.natice.noaa.gov/
IMAGE CAPTIONS:
[Image 1:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html]
The break-up of B-15A in progress off Cape Adare on 30 October 2005, as
seen Envisat's ASAR in Wide Swath Mode.
Credits: ESA
[Image 2:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html#subhead1]
Individual pieces of B-15A moving northward by currents from Cape Adare, 3
November, seen in this Envisat ASAR Global Monitoring Mode image. The
knife-shaped iceberg towards the bottom of the image is B-15K, a separate
iceberg from the original B-15 iceberg which is unconnected to the recent
B-15A break-up.
Credits: ESA
[Image 3:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html#subhead2]
The 27-28 October break-up of B-15A occurred off Cape Adare, the
northernmost extent of Queen Victoria Land, close to the former base of
Cape Hallett. The original B-15 calved from the Ross Ice Shelf to the
south, facing the Ross Sea, back in May 2000.
[Image 4:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html#subhead3]
B-15A still appeared intact in this Envisat ASAR image acquired 27 October
in Global Monitoring Mode.
Credits: ESA
[Image 5:
http://www.esa.int/esaCP/SEMCYK638FE_index_1.html#subhead4]
The break-up of B-15A has started in this Envisat ASAR image acquired 28
October in Global Monitoring Mode. The splits are likely to have occurred
along existing lines of weakness in the stranded iceberg.
Credits: ESA