Gravity Gradient Analysis at the GOCE HPF.pdf

EGU, Session G7, 7 May 2010
Gravity Gradient Analysis at
the GOCE HPF
J. Bouman, S. Rispens, P. Visser,
M.Veicherts, C.C. Tscherning, R. Pail,
R. Mayrhofer, Th. Gruber, E. Schrama, M. Fuchs
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

This presentation
Analysis of GOCE gravity gradients
31 October 2009 – 11 January 2010
External calibration results
Assessment of gravity gradient
accuracy
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

Temporal corrections
Gravity Gradient Preprocessing
Outliers, data gaps External calibration
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010
Frame trafo
EGG_TRF_2
EGG_NOM_2

EGG_NOM_2 & EGG_TRF_2
• EGG_NOM_2:
– Given in instrument frame (GRF)
– Accurate: V XX, V YY, V ZZ, V XZ; less accurate: V XY, V YZ
– Error increase at long wavelengths
• EGG_TRF_2:
– Given in Local North-Oriented Frame
– GGs V XY, V YZ: GOCE gravity model
– Long wavelength GG signal: GOCE gravity model
– GG error expected to be more homogeneous
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

EGG_NOM_2 & EGG_TRF_2
• EGG_NOM_2:
– Given in instrument frame (GRF)
– Accurate: V XX, V YY, V ZZ, V XZ; less accurate: V XY, V YZ
– Error increase at long wavelengths
• EGG_TRF_2:
– Given in Local North-Oriented Frame
– GGs V XY, V YZ: GOCE gravity model
– Long wavelength GG signal: GOCE gravity model
– GG error expected to be more homogeneous
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

EGG_NOM_2:
3 revolutions November 1, 2009
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

External calibration (1)
Global gravity field models (EIGEN5C)
• Weekly GG scale factors (10 in total)
• Gradiometer SF in-flight calibration 10 -4
• Confirmed by external calibration using global
gravity field models to 10 -3
Diagonal gravity gradients Off-diagonal gravity gradients
GG Mean Std
Vxx 1.002 3*10 -4
Vyy 1.001 8*10 -4
Vzz 1.001 4*10 -4
GG Mean Std
Vxy 1.003 0.014
Vxz 1.001 4*10 -4
Vyz 1.005 0.017
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

External calibration (2)
GOCE GPS data
• Estimation of global 80 x 80 gravity field
combining GOCE GPS data and GGs
• GG scale factors co-estimated
• 61 day repeat has 20 day sub-cycle: gravity field
and GG SFs every 20 days
Diagonal gravity gradients
GG Mean Std
Vxx 1.007 8*10 -3
Vyy 1.005 4*10 -3
Vzz 1.003 2*10 -3
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

External calibration (3): Terrestrial gravity data
• For each track in area GG SF estimated
• SF accepted if [0.9 – 1.1]
• SF of accurate GGs reliable (10 -2 level)
• SF of less accurate GGs unreliable (5 – 10%
accepted)
Calibration areas
Canada (134 tracks)
GG % Mean Std
Vxx 93 1.02 0.04
Vyy 87 0.99 0.04
Vzz 90 1.01 0.04
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

GOCE QL gravity model:
• GGs and GPS tracking
• Data from November and
December 2009
• SH degree 200
• Error assessment using
GG residuals
Estimated GG error SDs
V XX, V YY, V ZZ
Measurement
Band (MB)
• V XX and V YY same noise level in MB, V ZZ 2x larger
• Noise reduction in upper MB is “work in progress”
(Fehringer et al, Floberghagen et al, earlier this morning)
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

EGG_NOM_2 & EGG_TRF_2
• EGG_NOM_2:
– Given in instrument frame (GRF)
– Accurate: V XX, V YY, V ZZ, V XZ; less accurate: V XY, V YZ
– Error increase at long wavelengths
• EGG_TRF_2:
– Given in Local North-Oriented Frame
– GGs V XY, V YZ: GOCE QL gravity field model
– Long wavelength GG signal: GOCE gravity model
– GG error expected to be more homogeneous
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

EGG_NOM_2 & EGG_TRF_2:
3 revolutions November 1, 2009
EGG_NOM_2 EGG_TRF_2
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

EGG_TRF_2: compared with EIGEN5C
V XX differences GOCE & EIGEN5C
Binned averages 31 October 2009 - 11 January 2010
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010
[mE]

EGG_TRF_2: compared with EIGEN5C
V YY differences GOCE & EIGEN5C
Binned averages 31 October 2009 - 11 January 2010
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010
[mE]

EGG_TRF_2: compared with EIGEN5C
V ZZ differences GOCE & EIGEN5C
Binned averages 31 October 2009 - 11 January 2010
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010
[mE]

EGG_TRF_2: V XX compared with EIGEN5C
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

EGG_TRF_2: V YY compared with EIGEN5C
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

Summary
• GOCE gravity gradients in GRF and LNOF
(EGG_NOM_2 & EGG_TRF_2)
• November 2009 – January 2010 timeframe
• Differences with EIGEN5C (Africa, Himalaya, …)
• Error level V ZZ about 2x that of V XX, V YY in MB
• Spurious tracks V YY close to magnetic poles:
– Not well understood
– Very likely related to magnetic field
– Seems to diminish after in-flight calibration 11/12 January 2010
• Overall, GG data look very good
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

Back-up slides follow
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

SD Vzz, 1 day
SDs Vzz temporal
corrections, 1 day
Vzz time series, 1 day
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010

EGG_TRF_2: compared with EGM2008
V XX differences GOCE & EGM2008 (N = 360)
Binned averages 31 October 2009 - 11 January 2010
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010
[mE]

EGG_TRF_2: compared with EGM2008
V YY differences GOCE & EGM2008 (N = 360)
Binned averages 31 October 2009 - 11 January 2010
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010
[mE]

EGG_TRF_2: compared with EGM2008
V ZZ differences GOCE & EGM2008 (N = 360)
Binned averages 31 October 2009 - 11 January 2010
Bouman et al, GOCE Gravity Gradients, Session G7, EGU Vienna, 7 May 2010
[mE]