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Determination of Gravity Variations in Northern Europe from GRACE
Determination of Gravity Variations in Northern Europe from GRACE
Jürgen Müller, Matthias Neumann-Redlin
Institut für Erdmessung, University of Hannover, Germany([email protected])
Meeting of NKG Geodynamics WG, March 2006, AS, Norway
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Introduction
GRACE Results
Conclusions
Contents Contents
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Observation of GIA-Induced EffectsObservation of GIA-Induced Effects
Land uplift (1 cm / year)
Observed by
- GPS
- GRACE
- terrestrial gravimetry g = ± 2 Gal
Scherneck et al., 2003
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Difference Between Terrestrial and GRACE DataDifference Between Terrestrial and GRACE Data
Absolute gravimetry
- point-wise observations
- also local and regional effects
- high-frequency signals
GRACE
- spatial solution (spherical harmonics)
- long spatial wavelengths
- more low-frequency temporal signals
appropriate reductions required as well as temporal and spatial filtering
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GRACEGRACE
Launch: March 2002
1cm-geoid with a spatial resolution of 200 km and
temporal variations
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Spectral Characteristics of Temporal EffectsSpectral Characteristics of Temporal Effects
GRACE error curves compared to various signal curves
Spectra provided by GFZ Potsdam
GRACE
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GRACE Monthly SolutionsGRACE Monthly Solutions
Year1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6
7 8 9 10 11 12 13 14 15 16 171 2 3 4 5 6 7 8 9 101 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 1118 19 20 21 22 23 24 25 26 27 28 2911 12 13 14 15 16 17 18
11 12 13 14 15 1612 13 14 15 16 17 18 1930 31 3219 20 21 2217 18 19 20 21 22 23 24 25 26 2720 21 22 23 24 25 26 27
= CSR_old = CSR_new = GFZ = JPL
20
03
20
04
20
05
Available monthly GRACE-solutionsMonths
20
02
atmospheric and oceanic effects and tides already
reduced using models
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GRACE: Temporal Gravity Changes (L/2 = 1500 km)GRACE: Temporal Gravity Changes (L/2 = 1500 km)
Residual signal(hydrology)
[units: Gal]
Ocean, atmosphere
Gravity differences of GRACE monthly solutions
July – Sept. 2003
From CSR Solutions
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Analysis of Monthly GRACE SolutionsAnalysis of Monthly GRACE Solutions
• secular and periodic variations
• Least-squares adjustment
t = monthsω1 = 2π/6 = semi-annual periodω2 = 2π/12 = annual periodA, B, C, D, E, F = unknowns
)tsin(F)tcos(E)tsin(D)tcos(CtBA)t,,(dg 2211
Amp_6 = D²C² Amp_12 = F²E² Phase_12 =
FE
a tan
Trend = B
Errors13 nm/s² for gravity anomalies (Gauss filter 800 or 500 km)4 nm/s²/yr for secular variations3 nm/s² for amplitudes
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Temporal Gravity Variations in Northern EuropeTemporal Gravity Variations in Northern Europe
Secular gravity variations (trend/year) as derived from
GRACE data (Gauss filter 500 km)
Bild Landhebung
CSR (04/2002 – 03/2005) GFZ (02/2003 – 11/2005)
-15
0
15
5
10
-5
-10
[μGal/year]
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JPLGFZ
Secular variations [μGal/a]
CSR
Period: 02/2003 – 03/2005 (21 months)
Gaussian Filter: 500 km
Comparison of Latest ReleasesComparison of Latest Releases
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Different Gaussian Radii
500 km600 km
700 km800 km
GFZ (02/2003 – 11/2005)
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Periodic Gravity Variations in Northern Europe Periodic Gravity Variations in Northern Europe
[μGal][nm/s²]
Amplitudes
semi-annual annual
500 km
800 km
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annual phases
Periodic Gravity Variations in Northern Europe (2)Periodic Gravity Variations in Northern Europe (2)
Months related to January
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Contribution of Hydrology Contribution of Hydrology
amplitudes semi-annual
GRACE
WGHM
Amplitudes annual
[nm/s²]
0
10
20
0
10
20
8
0
5
2
8
0
5
2
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Contribution of Hydrology (2)Contribution of Hydrology (2)
GRACE
Secular gravity variations per year
WGHM GRACE-WGHM
(period: April 2002 – June 2004)
• Both data show trend at the same location• Signal is not in agreement with expected land uplift signal• Further effects have to be considered
-15
0
15
5
10
-5
-10
[nm/s²/year]
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Comparison with further Hydrological ModelsComparison with further Hydrological Models
WGHM GLDAS LaDWorld
GRACE-WGHM GRACE-LaDWorldGRACE-GLDAS
[nm/s²/year]
-15
0
15
5
10
-5-10
-15
0
15
5
10
-5-10
Secular gravity variations per year
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-50
-40
-30
-20
-10
0
10
20
30
40
1 5 6 7 8 9 10 11 12 13 14 16 17 18 19 20 21 22 23 24 25 26 27
Monate ( April 2002 - Juni 2004)
dg
[n
m/s
²]
GRACEWGHMGLDASLaDWorld
φ = 60°λ = 40°
Comparison with further Hydrological Models (2)Comparison with further Hydrological Models (2)
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900
910
920
930
940
950
960
970
980
990
1000
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33
months (02/2003 - 11/2005)
dg
[n
m/s
²]
gravity
gravity-corrected
Linear (gravity-corrected)Linear (gravity)
180
190
200
210
220
230
240
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33
months (02/2003 - 11/2005)
dg
[n
m/s
²]
gravity-corrected
gravity
Absolute Gravity Results - ExampleAbsolute Gravity Results - Example
Vaasa
Onsala
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Comparison with Absolute Gravity DataComparison with Absolute Gravity Data
• Absolute Gravity measurements with FG5-220 (IfE)
• Preliminary results, similar behaviour
• Further computations and investigations required
-50,00
-40,00
-30,00
-20,00
-10,00
0,00
10,00
20,00
30,00
40,00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33
months (02/2003 - 11/2005)
dg
[n
m/s
²]
GRACE-GFZ
absolute gravimetry
-30,00
-20,00
-10,00
0,00
10,00
20,00
30,00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33
months (02/2003 - 11/2005)
dg
[n
m/s
²]
GRACE-GFZ
absolute gravimetry
VaasaOnsala
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Determination of land uplift signal from GRACE data
Procedure
- Filtering of monthly GRACE solutions
- Errors of reduction models
- Models of further mass variations
- Spatial and temporal analyses of residuals
- Comparison with uplift models and independent data
- Extension of test area and generalisation of results
New Funding Project in Germany New Funding Project in Germany
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Monthly solutions: January 2003
Different Representations of Gravity
Gravity anomalies Gravity gradients [1/s²][m/s²]
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Difference: January 2004 - 2003
anomalies gradients
Different Representations of Gravity (2)
[1/s²][m/s²]
Difference: 0.2 mE
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Trend: Grace_Tzz (Gauss 500 km), [1/s2/year]
Different Representations of Gravity (3)
Difference: 0.06 mE/year
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Secular Mass Variations Siberia
WGHM_500_23GRACE_500_32
Trend caused by hydrological effects [water column in cm/a]
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Determination of land uplift signal from GRACE data is very challenging – also from ground.
Better GRACE models helpful
Dedicated filtering and processing required
Independent observations needed
Inter-disciplinary cooperations indispensable
Conclusions Conclusions
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Trend caused by hydrological effects [water column in cm/a]
Secular Mass Variations in Eurasia
GRACE_500_32 WGHM_500_23
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WGHM_500_23GRACE_500_32
σmax ≈ 1,2 cm
Annual amplitudes caused by hydrological effects [water column in cm/a]
Annual Mass Variations Siberia