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(mueller@ife.uni-hannover.de)

Meeting of NKG Geodynamics WG, March 2006, AS, Norway

Introduction

GRACE Results

Conclusions

Contents Contents

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

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

GRACEGRACE

Launch: March 2002

1cm-geoid with a spatial resolution of 200 km and

temporal variations

Spectral Characteristics of Temporal EffectsSpectral Characteristics of Temporal Effects

GRACE error curves compared to various signal curves

Spectra provided by GFZ Potsdam

GRACE

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

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

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

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]

JPLGFZ

Secular variations [μGal/a]

CSR

Period: 02/2003 – 03/2005 (21 months)

Gaussian Filter: 500 km

Comparison of Latest ReleasesComparison of Latest Releases

Different Gaussian Radii

500 km600 km

700 km800 km

GFZ (02/2003 – 11/2005)

Periodic Gravity Variations in Northern Europe Periodic Gravity Variations in Northern Europe

[μGal][nm/s²]

Amplitudes

semi-annual annual

500 km

800 km

annual phases

Periodic Gravity Variations in Northern Europe (2)Periodic Gravity Variations in Northern Europe (2)

Months related to January

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

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]

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

-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)

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

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

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

Monthly solutions: January 2003

Different Representations of Gravity

Gravity anomalies Gravity gradients [1/s²][m/s²]

Difference: January 2004 - 2003

anomalies gradients

Different Representations of Gravity (2)

[1/s²][m/s²]

Difference: 0.2 mE

Trend: Grace_Tzz (Gauss 500 km), [1/s2/year]

Different Representations of Gravity (3)

Difference: 0.06 mE/year

Secular Mass Variations Siberia

WGHM_500_23GRACE_500_32

Trend caused by hydrological effects [water column in cm/a]

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

Trend caused by hydrological effects [water column in cm/a]

Secular Mass Variations in Eurasia

GRACE_500_32 WGHM_500_23

WGHM_500_23GRACE_500_32

σmax ≈ 1,2 cm

Annual amplitudes caused by hydrological effects [water column in cm/a]

Annual Mass Variations Siberia