monitoring north american geoid change progress in geoid modeling from satellite missions 2009...
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Monitoring North American Geoid Change
Progress in Geoid Modelingfrom Satellite Missions
2009 Workshop on Monitoring North American Geoid ChangeBoulder, Colorado
21-23 October 2009
John RiesCenter for Space Research
The University of Texas at Austin
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Monitoring North American Geoid Change
• Mission Highlights
– Geoid models
• Mean fields: GGM03C, EIGEN-GL05C, ITG-GRACE03SEGM2008
• Time variable fields (86 monthly solutions through August 2009)
– Nearly 100 % of scientific measurements for over seven years have been collected and analyzed
• NASA 2009 Senior Review successful
– Extension to 2011 approved by NASA
– DLR approved mission funding through 2009• Last steps being taken to assure funding past 2009
• Flight Segment Generally Robust
– All systems in nominal operation
– Certain sub-systems are single-string on both s/c
– New thermal regimes to conserve battery life
– Instrument performance continues to meet mission requirements
GRACE Mission StatusOrbitLaunched: March 17, 2002 Over 7 years in orbit
Initial Altitude: 500 km Current Altitude: ~460 km (-10 m/day)Inclination: 89º Eccentricity: ~0.001Separation Distance: ~220 kmNon-Repeat Ground Track, Earth Pointed, 3-Axis Stable
Predicted Lifetime: 2013+
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Monitoring North American Geoid Change
Progress from EGM96
GFZ05C=EIGEN-GL05C
more power
improvement
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Monitoring North American Geoid Change
Improvement in GRACE-only Models
mgal
GGM01S-EGM96(deg/order 120)
GGM03S-EGM96(deg/order 120)
GGM02S-EGM96(deg/order 120)
Scale is +/- 10 mgal
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Monitoring North American Geoid Change
Progress in Gravity Determination from Space
GGM01S(111 days of GRACE data)
GGM03S(4 years of GRACE data)
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Monitoring North American Geoid Change
Estimated Total Geoid Error
GFZ05C=EIGEN-GL05C
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Monitoring North American Geoid Change
Degree-banded GPS Leveling TestLimiting the test to a selected degree range using a degree-banded approach
(Huang et al., 2002), 1149 GPS/leveling points over Canada were compared to the GGM02C, EIGEN-GL04C, and EGM2008 geoids
12
13
14
15
16
17
18
19
80 120 160 200 240 280 320 360
Canada
GGM02C
GFZ04C
EGM08
RM
S (
cm)
Degree
11.5
12
12.5
13
13.5
14
14.5
15
15.5
80 120 160 200 240 280 320 360
US
GGM02C
GFZ04C
EGM08
RM
S (
cm)
Degree
With EGM08, test now appears to be limited by GPS/leveling data errors, not geoid
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Monitoring North American Geoid Change
Short Wavelength Marine Geoid ResidualsEIGEN-GL04C
The residuals are the difference between a ‘high-frequency DOT’ defined as (GSFCMSS00 – geoid) and the same DOT smoothed to ~900 km
Scale is +/- 25 cm
‘Blending’ space-based and terrestrial gravity information smoothly and without ‘artifacts’ has been one of the most significant challenges
(to degree/order 360)
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Monitoring North American Geoid Change
Short Wavelength Marine Geoid ResidualsEIGEN-GL05C
The residuals are the difference between a ‘high-frequency DOT’ defined as (GSFCMSS00 – geoid) and the same DOT smoothed to ~900 km
Scale is +/- 25 cm.
As GRACE component becomes more accurate and skill in blending the two pieces of information improves, ‘artifacts’ are greatly reduced
(to degree/order 360)
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Monitoring North American Geoid Change
Short Wavelength Marine Geoid ResidualsEGM2008
The residuals are the difference between a ‘high-frequency DOT’ defined as (GSFCMSS00 – geoid) and the same DOT smoothed to ~900 km
Scale is +/- 25 cm.
EGM2008 is relatively free of ‘artifacts’ while also providing the most accurate and highest resolution marine geoid model (degree/order 2159+)
(to degree/order 360)
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Monitoring North American Geoid Change
microgal
Difference between two 2-year means (2003-2004 and 2005-2006)
Secular Gravity Changes (1)
Arctic and North America Antarctic
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Monitoring North American Geoid Change
Difference between two 2-year means (2003-2004 and 2005-2006)
Secular Gravity Changes (2)
Europe Asia
microgal
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Monitoring North American Geoid Change
Secular Gravity Changes (3)
Long-term geoid change dueto ∆J2 ~ 0.2 mm/yr
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Monitoring North American Geoid Change
Seasonal Geoid Variations
Mass variations are observed in Amazon basin with ~400 km resolution
A clear separation can be observed between the large Amazon watershed and the smaller watersheds to the north (e.g., the Orinoco
watershed), indicating that basin-scale variability is resolved.
1 mm geoid ≈ 2 cm water
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Monitoring North American Geoid Change
Gravity field and steady-state OceanCirculation Explorer (GOCE)
• Launched March 2009
• Drag-free mode May 2009– Allows operation at ~270 km
• Measurement mode September 2009
• Mission lifetime ~18 months
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Monitoring North American Geoid Change
Impact of GOCE on Geoid Accuracy
Combining GOCE with GRACE is expected to extend geoid resolution from space by a factor of 2 or more
Note that the long wavelength geoid information (including temporal variability) must be provided by
GRACE-type missions
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Monitoring North American Geoid Change
In The Near Future
• Continue routine operations and delivery of good quality data and products
– RL05, Quick-Look fields, and other exciting developments…
– Extension of Memorandum of Understanding between NASA and DLR on extended GRACE mission operations
– Closely monitor data and products for any signs of aging or environmentally related degradation in quality
• GRACE Science Team Meeting: Nov 5-6, in Austin, TX (USA)
– http://www.csr.utexas.edu/grace/GSTM
– Registration is now open
• Looking forward to the contribution of GOCE to geoid accuracy