The Variability of Sea Ice from Aqua’s AMSR-E Instrument:
A Quantitative Comparison of the Team and Bootstrap Algorithms
By Lorraine M. BeaneDr. Claire L. Parkinson, advisor
Research and Discover ProgramAugust 12, 2004
(Image courtesy of NOAA)Supported by the Research and Discover Program
Sea Ice• Formed by the freezing of sea water
– As freezing occurs, some of the salt drops down, leaving a layer of higher salinity water underneath the less saline ice (first year ice salinity is 10 ppt, multiyear ice salinity is 3 ppt)
• Found primarily in Arctic and Antarctic regions
• Spreads over approximately 25 million km2
• Growth in the first year can be 1-2 meters, although typically does not reach thicknesses of > 5 meters
• Average lifespan is 3-5 years
Sea Ice Impacts on Climate Change• Insulator of oceans at high
latitudes– Feedback effects
• Highly reflective surface reduces amount of absorbed solar radiation
• Affects much of the Earth’s deep ocean waters due to salt release– Stratification of the oceans– Global circulation patterns
• General trends since late 1978 show that sea ice is decreasing in the Arctic and increasing in the Antarctic
• The GCM at NASA Goddard Institute for Space Studies (GISS) indicates that as much as 37% of simulated global temperature rise is due to sea ice changes and the feedback effects they have on the rest of the system (Rind et al., 1995)
from C. Parkinson, D. Cavalieri,
J. Comiso, P. Gloersen, and J. Zwally
Sea Ice Observation• Monitoring of sea ice is possible in the visible spectrum,
but is often problematic due to cloud cover and darkness– This obstacle is overcome by using the microwave portion of the
EM spectrum– Brightness temperature is a measure of radiation in temperature
units
• Record is extensive and nearly continuous– Began in December 1972; most complete since late October 1978– Most recent data is from the Aqua spacecraft
www.thinkquest.org
Aqua• Launched on May 4, 2002
into a near polar orbit– Sea ice observation carried
out using the Advanced Microwave Scanning Radiometer (AMSR-E)
• Developed by Mitsubishi Electric Corporation under a contract from the National Space Development Agency of Japan (NASDA), subsequently merged into the Japan Aerospace Exploration Agency (JAXA)
• Passive microwave radiometer• Two products are developed
from this raw data to determine sea ice concentration using algorithms
http://aqua.gsfc.nasa.gov
Algorithms
• Two products are the ice coverages given by the Team and Bootstrap algorithms– Team is the standard in the Arctic– Bootstrap is standard in the Antarctic
• Used to determine sea ice concentration and extent…not thickness
• Both use the 19 GHz and 37 GHz frequencies– Team also uses 85 GHz– Bootstrap also uses 6 GHz
• Each uses different reference brightness temperatures, channel combinations, and weather filters
Goals of Research
• To conduct a quantitative investigation into the differences between the Team and Bootstrap algorithm results– Where do they differ?– How do they differ?– Are there differences in their behavior
between the two poles?– Are there any trends in their behavior?
June 2002 Northern Hemisphere
June 2002 differences in the Northern Hemisphere
Team – Bootstrap
Percent difference (%)
# of
hits
December 2002 Southern Hemisphere
December 2002 differences in the Southern Hemisphere
Percent difference (%)
# of
hits
Team - Bootstrap
Seasonal Variability of Sea Ice for 2002J J A S O N D
J J A S O N D
J J A S O N D
Comparison of ice coverage for the Northern Hemisphere June - December 2002
0
3
6
9
12
15
18
21
Jun Jul Aug Sep Oct Nov Dec
month
tota
l ice
cov
erag
e(1
0^6
squa
re k
m)
Team
Bootstrap
Comparison of ice coverage for the Southern Hemisphere June - December 2002
0
3
6
9
12
15
18
21
Jun Jul Aug Sep Oct Nov Dec
month
tota
l ice
cov
erag
e(1
0^6
squa
re k
m)
Team
Bootstrap
June 2002 percentage comparisonNorthern Hemisphere
0
20
40
60
80
100
120
percentage range
ice
cove
rage
(10
^5 s
quar
e km
) Team
Bootstrap
December 2002 percentage comparisonSouthern Hemisphere
0
25
50
75
100
125
150
percentage range
ice
cove
rage
(10
^5 s
quar
e km
) Team
Bootstrap
Conclusions
• Overall, both algorithms show very similar sea ice coverage, with the Bootstrap yielding slightly higher total ice coverage for the months examined
• Most often the Bootstrap algorithm shows a more extensive coverage at lower concentrations and a less extensive coverage at the 90-100% range
More Conclusions
• In the Northern Hemisphere – The Bootstrap yields higher concentrations over the
majority of the region, typically <10% difference– The Team yields higher concentrations over the peripheral
regions with differences up to around 20%
• In the Southern Hemisphere– The Team gives concentrations of 2-10% higher for a large
portion of the hemisphere– Occasionally the Bootstrap shows higher concentrations
along the edges of the ice and also in the Weddell and Ross seas, at least in the months examined
Further Analysis
• Completion of reprocessing of data in order to complete this analysis for an entire year – Seasonal variations– Comparisons of the same seasons at opposite poles
(i.e. summer in the Arctic versus summer in the Antarctic)
• Validation from the field– Efforts underway for both hemispheres, primarily via
aircraft flyovers• Arctic campaigns 2002-2005• Antarctic campaign scheduled for September 2004
Thanks and Acknowledgements
• Dr. Claire L. Parkinson• Nick DiGirolamo• Dr. Donald J. Cavalieri and Alvaro Ivanhoff• Dr. Josefino C. Comiso and Rob Gersten • Dr. George Hurtt and Dr. Vince Salomonson of
the Research and Discover Program• NASA Goddard Space Flight Center • University of New Hampshire
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