Iceberg's end caught by Envisat (Forwarded)

ESA News
http://www.esa.int

10 November 2003

Iceberg's end caught by Envisat

ESA's Envisat satellite was witness to the dramatic last days of what was once
the world's largest iceberg, as a violent Antarctic storm cracked a 160-km-long
floe in two.

A series of Envisat Advanced Synthetic Aperture Radar (ASAR) instrument images
acquired between mid-September and October record how the bottle-shaped iceberg
B-15A was split by the onslaught of powerful storms, waves and ocean currents as
its own weight kept it fixed on the floor of Antarctica's Ross Sea.

ASAR is especially useful for polar operations because its radar signal can
pierce thick clouds and works through both day and night. Radar imagery charts
surface roughness, so can easily differentiate between different ice types. Old
ice -- as on the surface of B-15A -- is rougher than newly formed ice.

B-15A began its existence as B-15 in March 2000 -- with an area of 11,655 sq km
it was the world's largest known iceberg. This Jamaica-sized floe was created
when it broke away from the Ross Ice Shelf. The initial monster berg split into
numerous pieces shortly afterwards, with the largest piece designated B-15A.

Like a wall of ice, B-15A remained a stubborn presence for the next two and a
half years, diverting ocean currents. This caused increased ice around Ross
Island that disrupted breeding patterns for the local penguin colony and
required extra icebreaker activity to maintain shipping access to the US base at
McMurdo Sound.

B-15A's end came in sight on 7 October this year, as 120 kph winds buffeted the
grounded iceberg during a storm. Two cracks ran into the heart of the iceberg
from opposite ends until finally the entire berg gave way.

The larger of the two new pieces has inherited the name B-15A, and the smaller
berg named B-15J. They remain largely locked in place, some 3,800 kilometres
south of New Zealand. The bergs could persist there for many years -- a GPS
station has been placed on the 3,496 sq km B-15A to enable study of its future
progress.

Despite events such as these there is so far no conclusive evidence as to
whether polar ice is actually thinning. Next year will see the launch of ESA’s
CryoSat mission, a dedicated ice-watching satellite designed to map precise
changes in the thickness of polar ice-sheets and floating sea-ice.

CryoSat will be the first satellite to be launched as part of the Agency’s
Living Planet Programme. This small research mission will carry a radar
altimeter that is based on a heritage from existing instruments, but with
several major enhancements to improve the measurement of icy surfaces.

By determining rates of ice-thickness change CryoSat will contribute to our
understanding of the relationship between the Earth’s ice cover and global climate.

Related articles

* Giants joust in the cold
http://www.esa.int/esaCP/ESAAQTTHN6D_index_0.html

Related links

* ASAR explained
http://www.esa.int/esaCP/ESAZGOG18ZC_FeatureWeek_0.html
* Eduspace -- Radar technology
http://www.eduspace.esa.int/eduspace...p?document=323
* B-15 observed from ERS-2
http://www.atsr.rl.ac.uk/images/sample/ross/index.shtml
* CryoSat
http://www.esa.int/esaLP/cryosat.html

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEMCPWWLDMD...reWeek_1.html]
This animation of iceberg B-15A breaking up was put together from 12 separate
ASAR images acquired by Envisat between 11 September and 12 October 2003.

Credits: ESA 2003

[Image 2:
http://www.esa.int/esaCP/SEMCPWWLDMD...html#subhead1]
Another Envisat instrument known as MERIS acquired this optical image showing
B-15A in the Ross Sea on 16 October 2003. The bottle-shaped iceberg can be seen
centre. Below it is the Ross Ice Sheet from which the B-15 berg originated in
March 2003. Left of B-15A is McMurdo Sound, location of US and New Zealand
Antarctic bases.

Credits: ESA 2003

[Image 3:
http://www.esa.int/esaCP/SEMCPWWLDMD...html#subhead2]
This ASAR image from 6 November 2003 clearly shows the split iceberg. The larger
piece of B-15A retains the original name, while the other piece is called B-15J.
Left of B-15A can be seen land -- including the famous McMurdo Dry Valleys, and
behind them the Transantarctic Mountains. Top of the picture is the floating
Drygalski Ice Tongue, an example of ice draining from the David Glacier into the
sea at a minimum rate of 150 metres a year.

Credits: ESA 2003

[Image 4:
http://www.esa.int/esaCP/SEMCPWWLDMD...html#subhead3]
CryoSat is the first satellite of ESA's Living Planet Programme to be realized
in the framework of the Earth Explorer Opportunity Missions. The mission concept
was selected in 1999 with an anticipated launch in 2004. CryoSat is a radar
altimetry mission dedicated to the observation of the polar regions. Its aim is
to study possible climate variability and trends by determining the variations
in thickness of the Earth's continental ice sheets and marine sea ice cover.