Analysis of gravity field variations derived from Superconducting Gravimeter recordings, the GRACE satellite and hydrological models at selected European sites

Abstract

If we restrict the spatial resolution to a half-wavelength of about 1500 km and the temporal resolution to 1 month, GRACE-derived temporal gravity variations can be resolved within the μgal (10 −8 m/s 2 ) range. A comparison with ground gravity measurements from selected Superconducting Gravimeter (SG) stations forming the Global Geodynamics Project (GGP) provides an independent validation. For this study, five European SGstations were selected that both cover a large test field and allow closely located SG-stations to be studied. Prior to this comparison, GRACE and SG data sets have to be reduced for the same known gravity effects due to Earth and ocean tides, pole tide, and atmosphere. After these reductions, the remaining part can be mainly attributed to mass changes in terrestrial water storage. For this reason, gravity variations derived from global hydrological models are included in the comparison of SG and GRACE results. Conversely, the hydrology models can be checked by gravity variations determined from GRACE and SG observations. For most of the SG locations investigated here, the comparison based primarily on computed correlations shows quite a good agreement among the gravity variation derived from the three different kinds of data sets: SG, GRACE, and hydrology models. The variations in SG gravity (point measurements) prove to be representative for a large area within the μgal accuracy range, if local gravity effects are removed correctly. Additionally, a methodology for an analysis of dominant common features based on the EOF-technique is proposed and illustrated. The first principal component shows strong periodicity, and the search for arbitrary periods confirms a strong common annual component, which reduces the total signal content considerably. The first eigenvector reveals common features and differences between distinct SG stations. Discrepancies between SG, GRACE, and hydrology models at individual SG stations, detected by both methods, may provide valuable hints for further investigations of respective data series.

Gravity field variations from superconducting gravimeters for GRACE validation

“…For a comparison with the GRACE-derived gravity changes the monthly solutions by GFZ (RL04) are used, smoothed by Gaussian filter of half-widths analogous to the degrees l l l l fl = 10, 13, and 20 (Neumeyer et al, 2008;Schmidt et al, 2008). A principle good agreement with the terrestrial SG gravity residuals exists for the degrees l l l l fl = 10 and l l l l fl = 13.…”

Time series of superconducting gravimeters and water storage variations from the global hydrology model WGHM

“…Initially treated as a disturbing effect in the analysis of the Earth and ocean tides and the interpretation of long-term gravity changes, this signal is considered today as valuable information to quantify mass changes of the system Earth, to verify and improve models describing such processes or to supplement and validate other time-variable gravity field observations, e.g. results from the GRACE satellite mission (Neumeyer et al, 2008, Weise et al, 2009. Further on, the quantification of such mass variations is a prerequisite to infer height changes from gravity changes complementary to the results of geodetic space techniques.…”

Análise de deformação por variação do geopotencial: estudo de caso para o terremoto maule (Mw 8,8) com base em dados mensais da missão Grace

“…Também abordou os denominados números de Love de sobrecarga superficial (h, k e l) associados aos efeitos indiretos das massas deslocadas. Estes números são relevantes para processamento de gravimetria terrestre (gravimetros superconductores) (NEUMEYER et al, 2008). Este aspecto não foi considerado de forma direta nesta investigação.…”

“…Já o caso da missão GRACE, além de recuperar o campo estático, permite também conhecer as suas variações temporais, fornecendo soluções com resolução temporal de um mês ou maiores (SCHMIDT et al, 2005, RUMMEL et al, 2009. Neste contexto, a missão GRACE tem sido aplicada em diferentes campos, tais como: Hidrologia, Criosfera, Terra sólida e Oceanografia (AWANGE et al, 2008;RAMILLIEN et al, 2004;NAKAEGAWA, 2006;NEUMEYER et al, 2008;VELICOGNA e WAHR, 2006;PAULSON et al, 2007;HAN et al, 2006;BINGHAM e HUGHES, 2006). Uma das vantagens do uso de dados de satélites gravitacionais é a cobertura no domínio do espaço e do tempo de variaçoes gravitacionais.…”