TY  - JOUR
A1  - Kurtenbach, E.
A1  - Eicker, A.
A1  - Mayer-Guerr, T.
A1  - Holschneider, Matthias
A1  - Hayn, M.
A1  - Fuhrmann, M.
A1  - Kusche, J.
T1  - Improved daily GRACE gravity field solutions using a Kalman smoother
JF  - Journal of geodynamics
N2  - Different GRACE data analysis centers provide temporal variations of the Earth's gravity field as monthly, 10-daily or weekly solutions. These temporal mean fields cannot model the variations occurring during the respective time span. The aim of our approach is to extract as much temporal information as possible out of the given GRACE data. Therefore the temporal resolution shall be increased with the goal to derive daily snapshots. Yet, such an increase in temporal resolution is accompanied by a loss of redundancy and therefore in a reduced accuracy if the daily solutions are calculated individually. The approach presented here therefore introduces spatial and temporal correlations of the expected gravity field signal derived from geophysical models in addition to the daily observations, thus effectively constraining the spatial and temporal evolution of the GRACE solution. The GRACE data processing is then performed within the framework of a Kalman filter and smoother estimation procedure.
 The approach is at first investigated in a closed-loop simulation scenario and then applied to the original GRACE observations (level-1B data) to calculate daily solutions as part of the gravity field model ITG-Grace2010. Finally, the daily models are compared to vertical GPS station displacements and ocean bottom pressure observations.
 From these comparisons it can be concluded that particular in higher latitudes the daily solutions contain high-frequent temporal gravity field information and represent an improvement to existing geophysical models.
KW  - GRACE
KW  - Daily gravity field
KW  - Kalman smoother
KW  - ITG-Grace2010
Y1  - 2012
U6  - https://doi.org/10.1016/j.jog.2012.02.006
SN  - 0264-3707
VL  - 59
IS  - 3
SP  - 39
EP  - 48
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Hayn, Michael
A1  - Panet, I.
A1  - Diament, M.
A1  - Holschneider, Matthias
A1  - Mandea, Mioara
A1  - Davaille, A.
T1  - Wavelet-based directional analysis of the gravity field  evidence for large-scale undulations
JF  - Geophysical journal international
N2  - In the eighties, the analysis of satellite altimetry data leads to the major discovery of gravity lineations in the oceans, with wavelengths between 200 and 1400 km. While the existence of the 200 km scale undulations is widely accepted, undulations at scales larger than 400 km are still a matter of debate. In this paper, we revisit the topic of the large-scale geoid undulations over the oceans in the light of the satellite gravity data provided by the GRACE mission, considerably more precise than the altimetry data at wavelengths larger than 400 km. First, we develop a dedicated method of directional Poisson wavelet analysis on the sphere with significance testing, in order to detect and characterize directional structures in geophysical data on the sphere at different spatial scales. This method is particularly well suited for potential field analysis. We validate it on a series of synthetic tests, and then apply it to analyze recent gravity models, as well as a bathymetry data set independent from gravity. Our analysis confirms the existence of gravity undulations at large scale in the oceans, with characteristic scales between 600 and 2000 km. Their direction correlates well with present-day plate motion over the Pacific ocean, where they are particularly clear, and associated with a conjugate direction at 1500 km scale. A major finding is that the 2000 km scale geoid undulations dominate and had never been so clearly observed previously. This is due to the great precision of GRACE data at those wavelengths. Given the large scale of these undulations, they are most likely related to mantle processes. Taking into account observations and models from other geophysical information, as seismological tomography, convection and geochemical models and electrical conductivity in the mantle, we conceive that all these inputs indicate a directional fabric of the mantle flows at depth, reflecting how the history of subduction influences the organization of lower mantle upwellings.
KW  - Wavelet transform
KW  - Satellite geodesy
KW  - Gravity anomalies and Earth structure
KW  - Pacific Ocean
Y1  - 2012
U6  - https://doi.org/10.1111/j.1365-246X.2012.05455.x
SN  - 0956-540X
SN  - 1365-246X
VL  - 189
IS  - 3
SP  - 1430
EP  - 1456
PB  - Oxford Univ. Press
CY  - Oxford
ER  -